feat(error): stack trace

fix: derivation & derivationStrict
feat: builtins.parseDrvName
2026-01-25 03:06:13 +08:00 · 2026-01-25 03:06:13 +08:00 · 2026-01-25 03:06:13 +08:00 · 2026-01-25 03:06:13 +08:00 · 2026-01-25 03:06:13 +08:00 · 2026-01-25 03:06:13 +08:00
31 changed files with 1466 additions and 537 deletions
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1927,11 +1927,11 @@ dependencies = [
 "rnix",
 "rowan",
 "rusqlite",
+ "rust-embed",
 "rustyline",
 "serde",
 "serde_json",
 "sha2",
- "sourcemap",
 "string-interner",
 "tar",
 "tempfile",
@@ -2587,6 +2587,40 @@ dependencies = [
 "smallvec",
 ]

+[[package]]
+name = "rust-embed"
+version = "8.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "04113cb9355a377d83f06ef1f0a45b8ab8cd7d8b1288160717d66df5c7988d27"
+dependencies = [
+ "rust-embed-impl",
+ "rust-embed-utils",
+ "walkdir",
+]
+
+[[package]]
+name = "rust-embed-impl"
+version = "8.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da0902e4c7c8e997159ab384e6d0fc91c221375f6894346ae107f47dd0f3ccaa"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "rust-embed-utils",
+ "syn",
+ "walkdir",
+]
+
+[[package]]
+name = "rust-embed-utils"
+version = "8.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5bcdef0be6fe7f6fa333b1073c949729274b05f123a0ad7efcb8efd878e5c3b1"
+dependencies = [
+ "sha2",
+ "walkdir",
+]
+
 [[package]]
 name = "rustc-demangle"
 version = "0.1.27"
--- a/nix-js/Cargo.toml
+++ b/nix-js/Cargo.toml
@@ -30,6 +30,8 @@ hashbrown = "0.16"
 petgraph = "0.8"
 string-interner = "0.19"

+rust-embed="8.11"
+
 itertools = "0.14"

 regex = "1.11"
@@ -41,7 +43,6 @@ nix-nar = "0.3"
 sha2 = "0.10"
 hex = "0.4"

-sourcemap = "9.0"
 base64 = "0.22"

 # Fetcher dependencies
--- a/nix-js/runtime-ts/src/builtins/attrs.ts
+++ b/nix-js/runtime-ts/src/builtins/attrs.ts
@@ -31,6 +31,7 @@ export const hasAttr =
  (set: NixValue): boolean =>
    Object.hasOwn(forceAttrs(set), forceStringValue(s));

+let counter = 0;
 export const mapAttrs =
  (f: NixValue) =>
  (attrs: NixValue): NixAttrs => {
@@ -38,7 +39,8 @@ export const mapAttrs =
    const forcedF = forceFunction(f);
    const newAttrs: NixAttrs = {};
    for (const key in forcedAttrs) {
-      newAttrs[key] = createThunk(() => forceFunction(forcedF(key))(forcedAttrs[key]));
+      newAttrs[key] = createThunk(() => forceFunction(forcedF(key))(forcedAttrs[key]), `created by mapAttrs (${counter})`);
+      counter += 1;
    }
    return newAttrs;
  };
@@ -49,9 +51,10 @@ export const removeAttrs =
    const new_attrs: NixAttrs = {};
    const forced_attrs = forceAttrs(attrs);
    const forced_list = forceList(list);
+    const keys_to_remove = new Set(forced_list.map(forceStringValue));

    for (const key in forced_attrs) {
-      if (!(key in forced_list)) {
+      if (!keys_to_remove.has(key)) {
        new_attrs[key] = forced_attrs[key];
      }
    }
@@ -104,3 +107,55 @@ export const groupBy =
    }
    return attrs;
  };
+
+export const zipAttrsWith =
+  (f: NixValue) =>
+  (list: NixValue): NixValue => {
+    const listForced = forceList(list);
+
+    // Map to collect all values for each attribute name
+    const attrMap = new Map<string, NixValue[]>();
+
+    // Iterate through each attribute set in the list
+    for (const item of listForced) {
+      const attrs = forceAttrs(item);
+
+      // Collect all attribute names and their values
+      for (const [key, value] of Object.entries(attrs)) {
+        if (!attrMap.has(key)) {
+          attrMap.set(key, []);
+        }
+        attrMap.get(key)!.push(value);
+      }
+    }
+
+    // Build the result attribute set
+    const result: Record<string, NixValue> = {};
+
+    for (const [name, values] of attrMap.entries()) {
+      // Apply f to name and values list
+      // f is curried: f name values
+      result[name] = createThunk(() => forceFunction(forceFunction(f)(name))(values));
+    }
+
+    return result;
+  };
+
+export const unsafeGetAttrPos =
+  (attrName: NixValue) =>
+  (attrSet: NixValue): NixValue => {
+    const name = forceStringValue(attrName);
+    const attrs = forceAttrs(attrSet);
+
+    if (!(name in attrs)) {
+      return null;
+    }
+
+    const positions = (attrs as any)[Nix.ATTR_POSITIONS];
+    if (!positions || !(name in positions)) {
+      return null;
+    }
+
+    const span = positions[name];
+    return Nix.mkPos(span);
+  };
--- a/nix-js/runtime-ts/src/builtins/conversion.ts
+++ b/nix-js/runtime-ts/src/builtins/conversion.ts
@@ -8,7 +8,7 @@ import { force } from "../thunk";
 import { type NixStringContext, mkStringWithContext, addBuiltContext } from "../string-context";
 import { forceFunction } from "../type-assert";
 import { nixValueToJson } from "../conversion";
-import { typeOf } from "./type-check";
+import { isAttrs, isPath, typeOf } from "./type-check";

 const convertJsonToNix = (json: unknown): NixValue => {
  if (json === null) {
@@ -283,6 +283,16 @@ export const coerceToStringWithContext = (
 * - Preserves string context if present
 */
 export const coerceToPath = (value: NixValue, outContext?: NixStringContext): string => {
+  const forced = force(value);
+
+  if (isPath(forced)) {
+    return forced.value;
+  }
+  if (isAttrs(forced) && Object.hasOwn(forced, "__toString")) {
+    const toStringFunc = forceFunction(forced.__toString);
+    return coerceToPath(toStringFunc(forced), outContext);
+  }
+
  const pathStr = coerceToString(value, StringCoercionMode.Base, false, outContext);

  if (pathStr === "") {
--- a/nix-js/runtime-ts/src/builtins/derivation.ts
+++ b/nix-js/runtime-ts/src/builtins/derivation.ts
@@ -1,9 +1,16 @@
 import type { NixValue, NixAttrs } from "../types";
 import { forceStringValue, forceList } from "../type-assert";
-import { force } from "../thunk";
+import { force, createThunk } from "../thunk";
 import { type DerivationData, type OutputInfo, generateAterm } from "../derivation-helpers";
 import { coerceToString, StringCoercionMode } from "./conversion";
-import { type NixStringContext, extractInputDrvsAndSrcs, isStringWithContext } from "../string-context";
+import {
+  type NixStringContext,
+  extractInputDrvsAndSrcs,
+  isStringWithContext,
+  mkStringWithContext,
+  addDrvDeepContext,
+  addBuiltContext,
+} from "../string-context";
 import { nixValueToJson } from "../conversion";
 import { isNixPath } from "../types";

@@ -88,6 +95,7 @@ const extractEnv = (
  structuredAttrs: boolean,
  ignoreNulls: boolean,
  outContext: NixStringContext,
+  drvName: string,
 ): Map<string, string> => {
  const specialAttrs = new Set([
    "name",
@@ -113,6 +121,49 @@ const extractEnv = (
        }
        jsonAttrs[key] = nixValueToJson(value, new Set(), outContext);
      }
+
+      if (key === "allowedReferences") {
+        console.warn(
+          `In a derivation named '${drvName}', 'structuredAttrs' disables the effect of ` +
+          `the derivation attribute 'allowedReferences'; use ` +
+          `'outputChecks.<output>.allowedReferences' instead`
+        );
+      }
+      if (key === "allowedRequisites") {
+        console.warn(
+          `In a derivation named '${drvName}', 'structuredAttrs' disables the effect of ` +
+          `the derivation attribute 'allowedRequisites'; use ` +
+          `'outputChecks.<output>.allowedRequisites' instead`
+        );
+      }
+      if (key === "disallowedReferences") {
+        console.warn(
+          `In a derivation named '${drvName}', 'structuredAttrs' disables the effect of ` +
+          `the derivation attribute 'disallowedReferences'; use ` +
+          `'outputChecks.<output>.disallowedReferences' instead`
+        );
+      }
+      if (key === "disallowedRequisites") {
+        console.warn(
+          `In a derivation named '${drvName}', 'structuredAttrs' disables the effect of ` +
+          `the derivation attribute 'disallowedRequisites'; use ` +
+          `'outputChecks.<output>.disallowedRequisites' instead`
+        );
+      }
+      if (key === "maxSize") {
+        console.warn(
+          `In a derivation named '${drvName}', 'structuredAttrs' disables the effect of ` +
+          `the derivation attribute 'maxSize'; use ` +
+          `'outputChecks.<output>.maxSize' instead`
+        );
+      }
+      if (key === "maxClosureSize") {
+        console.warn(
+          `In a derivation named '${drvName}', 'structuredAttrs' disables the effect of ` +
+          `the derivation attribute 'maxClosureSize'; use ` +
+          `'outputChecks.<output>.maxClosureSize' instead`
+        );
+      }
    }
    env.set("__json", JSON.stringify(jsonAttrs));
  } else {
@@ -174,8 +225,16 @@ export const derivationStrict = (args: NixValue): NixAttrs => {

  const ignoreNulls = "__ignoreNulls" in attrs ? force(attrs.__ignoreNulls) === true : false;

+  if ("__contentAddressed" in attrs && force(attrs.__contentAddressed) === true) {
+    throw new Error("ca derivations are not supported");
+  }
+
+  if ("impure" in attrs && force(attrs.impure) === true) {
+    throw new Error("impure derivations are not supported");
+  }
+
  const drvArgs = extractArgs(attrs, collectedContext);
-  const env = extractEnv(attrs, structuredAttrs, ignoreNulls, collectedContext);
+  const env = extractEnv(attrs, structuredAttrs, ignoreNulls, collectedContext, drvName);

  env.set("name", drvName);
  env.set("builder", builder);
@@ -277,37 +336,94 @@ export const derivationStrict = (args: NixValue): NixAttrs => {
    drvPath = Deno.core.ops.op_make_store_path("text", finalDrvHash, `${drvName}.drv`);
  }

-  const result: NixAttrs = {
-    type: "derivation",
-    drvPath,
-    name: drvName,
-    builder,
-    system: platform,
-  };
+  const result: NixAttrs = {};
+
+  const drvPathContext = new Set<string>();
+  addDrvDeepContext(drvPathContext, drvPath);
+  result.drvPath = mkStringWithContext(drvPath, drvPathContext);

  for (const [outputName, outputInfo] of outputInfos.entries()) {
-    result[outputName] = outputInfo.path;
-  }
-
-  if (outputInfos.has("out")) {
-    result.outPath = outputInfos.get("out")!.path;
-  }
-
-  if (drvArgs.length > 0) {
-    result.args = drvArgs;
-  }
-
-  if (!structuredAttrs) {
-    for (const [key, value] of env.entries()) {
-      if (!["name", "builder", "system", ...outputs].includes(key)) {
-        result[key] = value;
-      }
-    }
+    const outputContext = new Set<string>();
+    addBuiltContext(outputContext, drvPath, outputName);
+    result[outputName] = mkStringWithContext(outputInfo.path, outputContext);
  }

  return result;
 };

 export const derivation = (args: NixValue): NixAttrs => {
-  return derivationStrict(args);
+  const attrs = forceAttrs(args);
+  const strict = derivationStrict(args);
+
+  const outputs: string[] = extractOutputs(attrs);
+  const drvName = validateName(attrs);
+  const collectedContext: NixStringContext = new Set();
+  const builder = validateBuilder(attrs, collectedContext);
+  const platform = validateSystem(attrs);
+  const structuredAttrs = "__structuredAttrs" in attrs ? force(attrs.__structuredAttrs) === true : false;
+  const ignoreNulls = "__ignoreNulls" in attrs ? force(attrs.__ignoreNulls) === true : false;
+  const drvArgs = extractArgs(attrs, collectedContext);
+
+  const specialAttrs = new Set([
+    "name",
+    "builder",
+    "system",
+    "args",
+    "outputs",
+    "__structuredAttrs",
+    "__ignoreNulls",
+    "__contentAddressed",
+    "impure",
+  ]);
+
+  const baseAttrs: NixAttrs = {
+    type: "derivation",
+    drvPath: strict.drvPath,
+    name: drvName,
+    builder,
+    system: platform,
+  };
+
+  if (drvArgs.length > 0) {
+    baseAttrs.args = drvArgs;
+  }
+
+  if (!structuredAttrs) {
+    for (const [key, value] of Object.entries(attrs)) {
+      if (!specialAttrs.has(key) && !outputs.includes(key)) {
+        const forcedValue = force(value);
+        if (!(ignoreNulls && forcedValue === null)) {
+          baseAttrs[key] = value;
+        }
+      }
+    }
+  }
+
+  const outputsList: NixAttrs[] = [];
+
+  for (const outputName of outputs) {
+    const outputObj: NixAttrs = {
+      ...baseAttrs,
+      outPath: strict[outputName],
+      outputName,
+    };
+    outputsList.push(outputObj);
+  }
+
+  baseAttrs.drvAttrs = attrs;
+  for (const [i, outputName] of outputs.entries()) {
+    baseAttrs[outputName] = createThunk(() => outputsList[i], `output_${outputName}`);
+  }
+  baseAttrs.all = createThunk(() => outputsList, "all_outputs");
+
+  for (const outputObj of outputsList) {
+    outputObj.drvAttrs = attrs;
+    for (const [i, outputName] of outputs.entries()) {
+      outputObj[outputName] = createThunk(() => outputsList[i], `output_${outputName}`);
+    }
+    outputObj.all = createThunk(() => outputsList, "all_outputs");
+  }
+
+  return outputsList[0];
 };
+
--- a/nix-js/runtime-ts/src/builtins/index.ts
+++ b/nix-js/runtime-ts/src/builtins/index.ts
@@ -172,6 +172,8 @@ export const builtins: any = {
  intersectAttrs: mkPrimop(attrs.intersectAttrs, "intersectAttrs", 2),
  catAttrs: mkPrimop(attrs.catAttrs, "catAttrs", 2),
  groupBy: mkPrimop(attrs.groupBy, "groupBy", 2),
+  zipAttrsWith: mkPrimop(attrs.zipAttrsWith, "zipAttrsWith", 2),
+  unsafeGetAttrPos: mkPrimop(attrs.unsafeGetAttrPos, "unsafeGetAttrPos", 2),

  stringLength: mkPrimop(string.stringLength, "stringLength", 1),
  substring: mkPrimop(string.substring, "substring", 3),
@@ -231,7 +233,6 @@ export const builtins: any = {
    1,
  ),
  unsafeDiscardStringContext: mkPrimop(misc.unsafeDiscardStringContext, "unsafeDiscardStringContext", 1),
-  unsafeGetAttrPos: mkPrimop(misc.unsafeGetAttrPos, "unsafeGetAttrPos", 2),
  addDrvOutputDependencies: mkPrimop(misc.addDrvOutputDependencies, "addDrvOutputDependencies", 2),
  compareVersions: mkPrimop(misc.compareVersions, "compareVersions", 2),
  flakeRefToString: mkPrimop(misc.flakeRefToString, "flakeRefToString", 1),
@@ -247,13 +248,12 @@ export const builtins: any = {
  splitVersion: mkPrimop(misc.splitVersion, "splitVersion", 1),
  traceVerbose: mkPrimop(misc.traceVerbose, "traceVerbose", 2),
  tryEval: mkPrimop(misc.tryEval, "tryEval", 1),
-  zipAttrsWith: mkPrimop(misc.zipAttrsWith, "zipAttrsWith", 2),

-  builtins: createThunk(() => builtins),
+  builtins: createThunk(() => builtins, "builtins"),
  currentSystem: createThunk(() => {
    return "x86_64-linux";
-  }),
-  currentTime: createThunk(() => Date.now()),
+  }, "currentSystem"),
+  currentTime: createThunk(() => Date.now(), "currentTime"),

  false: false,
  true: true,
--- a/nix-js/runtime-ts/src/builtins/io.ts
+++ b/nix-js/runtime-ts/src/builtins/io.ts
@@ -3,15 +3,16 @@
 * Implemented via Rust ops exposed through deno_core
 */

-import { forceAttrs, forceBool, forceStringValue } from "../type-assert";
-import type { NixValue, NixAttrs } from "../types";
-import { isNixPath } from "../types";
+import { forceAttrs, forceBool, forceList, forceStringNoCtx, forceStringValue } from "../type-assert";
+import type { NixValue, NixAttrs, NixPath } from "../types";
+import { isNixPath, IS_PATH, CatchableError } from "../types";
 import { force } from "../thunk";
 import { coerceToPath, coerceToString, StringCoercionMode } from "./conversion";
 import { getPathValue } from "../path";
 import type { NixStringContext, StringWithContext } from "../string-context";
 import { mkStringWithContext } from "../string-context";
 import { isPath } from "./type-check";
+import { getCorepkg } from "../corepkgs";

 export const importFunc = (path: NixValue): NixValue => {
  const context: NixStringContext = new Set();
@@ -291,8 +292,14 @@ const autoDetectAndFetch = (attrs: NixAttrs): NixAttrs => {
  return { outPath: fetchurl(attrs) };
 };

-export const readDir = (path: NixValue): never => {
-  throw new Error("Not implemented: readDir");
+export const readDir = (path: NixValue): NixAttrs => {
+  const pathStr = coerceToPath(path);
+  const entries: Record<string, string> = Deno.core.ops.op_read_dir(pathStr);
+  const result: NixAttrs = {};
+  for (const [name, type] of Object.entries(entries)) {
+    result[name] = type;
+  }
+  return result;
 };

 export const readFile = (path: NixValue): string => {
@@ -300,8 +307,9 @@ export const readFile = (path: NixValue): string => {
  return Deno.core.ops.op_read_file(pathStr);
 };

-export const readFileType = (path: NixValue): never => {
-  throw new Error("Not implemented: readFileType");
+export const readFileType = (path: NixValue): string => {
+  const pathStr = coerceToPath(path);
+  return Deno.core.ops.op_read_file_type(pathStr);
 };

 export const pathExists = (path: NixValue): boolean => {
@@ -390,10 +398,70 @@ export const filterSource = (args: NixValue): never => {
  throw new Error("Not implemented: filterSource");
 };

+const suffixIfPotentialMatch = (prefix: string, path: string): string | null => {
+  const n = prefix.length;
+
+  const needSeparator = n > 0 && n < path.length;
+
+  if (needSeparator && path[n] !== "/") {
+    return null;
+  }
+
+  if (!path.startsWith(prefix)) {
+    return null;
+  }
+
+  return needSeparator ? path.substring(n + 1) : path.substring(n);
+};
+
 export const findFile =
-  (search: NixValue) =>
-  (lookup: NixValue): never => {
-    throw new Error("Not implemented: findFile");
+  (searchPath: NixValue) =>
+  (lookupPath: NixValue): NixPath => {
+    const forcedSearchPath = forceList(searchPath);
+    const lookupPathStr = forceStringNoCtx(lookupPath);
+
+    for (const item of forcedSearchPath) {
+      const attrs = forceAttrs(item);
+
+      const prefix = "prefix" in attrs ? forceStringNoCtx(attrs.prefix) : "";
+
+      if (!("path" in attrs)) {
+        throw new Error("findFile: search path element is missing 'path' attribute");
+      }
+
+      const suffix = suffixIfPotentialMatch(prefix, lookupPathStr);
+      if (suffix === null) {
+        continue;
+      }
+
+      const context: NixStringContext = new Set();
+      const pathVal = coerceToString(attrs.path, StringCoercionMode.Interpolation, false, context);
+
+      if (context.size > 0) {
+        throw new Error("findFile: path with string context is not yet supported");
+      }
+
+      const resolvedPath = Deno.core.ops.op_resolve_path(pathVal, "");
+      const candidatePath = suffix.length > 0
+        ? Deno.core.ops.op_resolve_path(suffix, resolvedPath)
+        : resolvedPath;
+
+      if (Deno.core.ops.op_path_exists(candidatePath)) {
+        return { [IS_PATH]: true, value: candidatePath };
+      }
+    }
+
+    if (lookupPathStr.startsWith("nix/")) {
+      const corepkgName = lookupPathStr.substring(4);
+      const corepkgContent = getCorepkg(corepkgName);
+
+      if (corepkgContent !== undefined) {
+        // FIXME: special path type
+        return { [IS_PATH]: true, value: `<nix/${corepkgName}>` };
+      }
+    }
+
+    throw new CatchableError(`file '${lookupPathStr}' was not found in the Nix search path`);
  };

 export const getEnv = (s: NixValue): string => {
--- a/nix-js/runtime-ts/src/builtins/misc.ts
+++ b/nix-js/runtime-ts/src/builtins/misc.ts
@@ -2,12 +2,12 @@
 * Miscellaneous builtin functions
 */

-import { force } from "../thunk";
+import { createThunk, force } from "../thunk";
 import { CatchableError } from "../types";
 import type { NixAttrs, NixBool, NixStrictValue, NixValue } from "../types";
-import { forceList, forceAttrs, forceFunction, forceStringValue, forceString } from "../type-assert";
+import { forceList, forceAttrs, forceFunction, forceStringValue, forceString, forceStringNoCtx } from "../type-assert";
 import * as context from "./context";
-import { compareValues, op } from "../operators";
+import { compareValues } from "../operators";
 import { isBool, isFloat, isInt, isList, isString, typeOf } from "./type-check";
 import { OrderedSet } from "js-sdsl";
 import {
@@ -15,13 +15,13 @@ import {
  getStringValue,
  getStringContext,
  mkStringWithContext,
-  mergeContexts,
 } from "../string-context";

 export const addErrorContext =
  (e1: NixValue) =>
-  (e2: NixValue): never => {
-    throw new Error("Not implemented: addErrorContext");
+  (e2: NixValue): NixValue => {
+    console.log("[WARNING]: addErrorContext not implemented");
+    return e2;
  };

 export const appendContext = context.appendContext;
@@ -50,10 +50,6 @@ export const unsafeDiscardOutputDependency = context.unsafeDiscardOutputDependen

 export const unsafeDiscardStringContext = context.unsafeDiscardStringContext;

-export const unsafeGetAttrPos = (s: NixValue): never => {
-  throw new Error("Not implemented: unsafeGetAttrPos");
-};
-
 export const addDrvOutputDependencies = context.addDrvOutputDependencies;

 export const compareVersions =
@@ -232,8 +228,21 @@ export const outputOf =
    throw new Error("Not implemented: outputOf");
  };

-export const parseDrvName = (s: NixValue): never => {
-  throw new Error("Not implemented: parseDrvName");
+export const parseDrvName = (s: NixValue): NixAttrs => {
+  const fullName = forceStringNoCtx(s);
+  let name = fullName;
+  let version = "";
+  for (let i = 0; i < fullName.length; ++i) {
+    if (fullName[i] === '-' && i + 1 < fullName.length && !/[a-zA-Z]/.test(fullName[i + 1])) {
+      name = fullName.substring(0, i);
+      version = fullName.substring(i + 1);
+      break;
+    }
+  }
+  return {
+    name,
+    version
+  }
 };

 export const parseFlakeName = (s: NixValue): never => {
@@ -355,37 +364,3 @@ export const tryEval = (e: NixValue): { success: NixBool; value: NixStrictValue
    }
  }
 };
-
-export const zipAttrsWith =
-  (f: NixValue) =>
-  (list: NixValue): NixValue => {
-    const listForced = forceList(list);
-
-    // Map to collect all values for each attribute name
-    const attrMap = new Map<string, NixValue[]>();
-
-    // Iterate through each attribute set in the list
-    for (const item of listForced) {
-      const attrs = forceAttrs(force(item) as NixValue);
-
-      // Collect all attribute names and their values
-      for (const [key, value] of Object.entries(attrs)) {
-        if (!attrMap.has(key)) {
-          attrMap.set(key, []);
-        }
-        attrMap.get(key)!.push(value);
-      }
-    }
-
-    // Build the result attribute set
-    const result: Record<string, NixValue> = {};
-
-    for (const [name, values] of attrMap.entries()) {
-      // Apply f to name and values list
-      // f is curried: f name values
-      const fWithName = forceFunction(f)(name);
-      result[name] = forceFunction(fWithName)(values);
-    }
-
-    return result;
-  };
--- a/nix-js/runtime-ts/src/corepkgs/fetchurl.nix.ts
+++ b/nix-js/runtime-ts/src/corepkgs/fetchurl.nix.ts
@@ -0,0 +1,73 @@
+export const FETCHURL_NIX = `{
+  system ? "", # obsolete
+  url,
+  hash ? "", # an SRI hash
+
+  # Legacy hash specification
+  md5 ? "",
+  sha1 ? "",
+  sha256 ? "",
+  sha512 ? "",
+  outputHash ?
+    if hash != "" then
+      hash
+    else if sha512 != "" then
+      sha512
+    else if sha1 != "" then
+      sha1
+    else if md5 != "" then
+      md5
+    else
+      sha256,
+  outputHashAlgo ?
+    if hash != "" then
+      ""
+    else if sha512 != "" then
+      "sha512"
+    else if sha1 != "" then
+      "sha1"
+    else if md5 != "" then
+      "md5"
+    else
+      "sha256",
+
+  executable ? false,
+  unpack ? false,
+  name ? baseNameOf (toString url),
+  impure ? false,
+}:
+
+derivation (
+  {
+    builder = "builtin:fetchurl";
+
+    # New-style output content requirements.
+    outputHashMode = if unpack || executable then "recursive" else "flat";
+
+    inherit
+      name
+      url
+      executable
+      unpack
+      ;
+
+    system = "builtin";
+
+    # No need to double the amount of network traffic
+    preferLocalBuild = true;
+
+    # This attribute does nothing; it's here to avoid changing evaluation results.
+    impureEnvVars = [
+      "http_proxy"
+      "https_proxy"
+      "ftp_proxy"
+      "all_proxy"
+      "no_proxy"
+    ];
+
+    # To make "nix-prefetch-url" work.
+    urls = [ url ];
+  }
+  // (if impure then { __impure = true; } else { inherit outputHashAlgo outputHash; })
+)
+`;
--- a/nix-js/runtime-ts/src/corepkgs/index.ts
+++ b/nix-js/runtime-ts/src/corepkgs/index.ts
@@ -0,0 +1,9 @@
+import { FETCHURL_NIX } from "./fetchurl.nix";
+
+export const COREPKGS: Record<string, string> = {
+  "fetchurl.nix": FETCHURL_NIX,
+};
+
+export const getCorepkg = (name: string): string | undefined => {
+  return COREPKGS[name];
+};
--- a/nix-js/runtime-ts/src/helpers.ts
+++ b/nix-js/runtime-ts/src/helpers.ts
@@ -169,7 +169,15 @@ export const concatStringsWithContext = (parts: NixValue[]): NixString | NixPath
 * @returns NixPath object with absolute path
 */
 export const resolvePath = (currentDir: string, path: NixValue): NixPath => {
-  const pathStr = forceStringValue(path);
+  const forced = force(path);
+  let pathStr: string;
+
+  if (isNixPath(forced)) {
+    pathStr = forced.value;
+  } else {
+    pathStr = forceStringValue(path);
+  }
+
  const resolved = Deno.core.ops.op_resolve_path(currentDir, pathStr);
  return mkPath(resolved);
 };
@@ -242,17 +250,20 @@ export const selectWithDefault = (
  }
 };

-function selectWithDefault_impl(obj: NixValue, attrpath: NixValue[], default_val: NixValue): NixValue {
-  let attrs = forceAttrs(obj);
+function selectWithDefault_impl(obj: NixValue, attrpath: NixValue[], defaultVal: NixValue): NixValue {
+  let attrs = force(obj);
+  if (!isAttrs(attrs)) {
+    return defaultVal;
+  }

  for (const attr of attrpath.slice(0, -1)) {
    const key = forceStringValue(attr);
    if (!(key in attrs)) {
-      return default_val;
+      return defaultVal;
    }
    const cur = force(attrs[key]);
    if (!isAttrs(cur)) {
-      return default_val;
+      return defaultVal;
    }
    attrs = cur;
  }
@@ -261,7 +272,7 @@ function selectWithDefault_impl(obj: NixValue, attrpath: NixValue[], default_val
  if (last in attrs) {
    return attrs[last];
  }
-  return default_val;
+  return defaultVal;
 }

 export const hasAttr = (obj: NixValue, attrpath: NixValue[]): NixBool => {
@@ -377,3 +388,7 @@ export const ifFunc = (cond: NixValue, consq: NixValue, alter: NixValue) => {
  }
  return alter;
 };
+
+export const mkPos = (span: string): NixAttrs => {
+  return Deno.core.ops.op_decode_span(span);
+};
--- a/nix-js/runtime-ts/src/index.ts
+++ b/nix-js/runtime-ts/src/index.ts
@@ -18,12 +18,13 @@ import {
  pushContext,
  popContext,
  withContext,
+  mkPos,
 } from "./helpers";
 import { op } from "./operators";
 import { builtins, PRIMOP_METADATA } from "./builtins";
 import { coerceToString, StringCoercionMode } from "./builtins/conversion";
 import { HAS_CONTEXT } from "./string-context";
-import { IS_PATH, mkFunction } from "./types";
+import { IS_PATH, mkAttrs, mkFunction, mkAttrsWithPos, ATTR_POSITIONS } from "./types";
 import { forceBool } from "./type-assert";

 export type NixRuntime = typeof Nix;
@@ -52,7 +53,11 @@ export const Nix = {
  coerceToString,
  concatStringsWithContext,
  StringCoercionMode,
+  mkAttrs,
+  mkAttrsWithPos,
  mkFunction,
+  mkPos,
+  ATTR_POSITIONS,

  pushContext,
  popContext,
--- a/nix-js/runtime-ts/src/type-assert.ts
+++ b/nix-js/runtime-ts/src/type-assert.ts
@@ -85,6 +85,17 @@ export const forceString = (value: NixValue): NixString => {
  throw new TypeError(`Expected string, got ${typeOf(forced)}`);
 };

+export const forceStringNoCtx = (value: NixValue): string => {
+  const forced = force(value);
+  if (typeof forced === "string") {
+    return forced;
+  }
+  if (isStringWithContext(forced)) {
+    throw new TypeError(`the string '${forced.value}' is not allowed to refer to a store path`)
+  }
+  throw new TypeError(`Expected string, got ${typeOf(forced)}`);
+}
+
 /**
 * Force a value and assert it's a boolean
 * @throws TypeError if value is not a boolean after forcing
--- a/nix-js/runtime-ts/src/types.ts
+++ b/nix-js/runtime-ts/src/types.ts
@@ -2,10 +2,11 @@
 * Core TypeScript type definitions for nix-js runtime
 */

-import { IS_THUNK } from "./thunk";
-import { type StringWithContext, HAS_CONTEXT, isStringWithContext } from "./string-context";
+import { force, IS_THUNK } from "./thunk";
+import { type StringWithContext, HAS_CONTEXT, isStringWithContext, getStringContext } from "./string-context";
 import { op } from "./operators";
-import { forceAttrs } from "./type-assert";
+import { forceAttrs, forceStringNoCtx } from "./type-assert";
+import { isString, typeOf } from "./builtins/type-check";
 export { HAS_CONTEXT, isStringWithContext };
 export type { StringWithContext };

@@ -62,11 +63,62 @@ export class NixArgs {
    }
  }
 }
-export const mkFunction = (f: (arg: NixValue) => NixValue, required: string[], optional: string[], ellipsis: boolean): NixFunction => {
+export const mkFunction = (
+  f: (arg: NixValue) => NixValue,
+  required: string[],
+  optional: string[],
+  ellipsis: boolean,
+): NixFunction => {
  const func = f as NixFunction;
  func.args = new NixArgs(required, optional, ellipsis);
-  return func
-}
+  return func;
+};
+
+export const mkAttrs = (attrs: NixAttrs, keys: NixValue[], values: NixValue[]): NixAttrs => {
+  const len = keys.length;
+  for (let i = 0; i < len; i++) {
+    const key = force(keys[i]);
+    if (key === null) {
+      continue;
+    }
+    const str = forceStringNoCtx(key);
+    attrs[str] = values[i];
+  }
+  return attrs;
+};
+
+const ATTR_POSITIONS = Symbol("attrPositions");
+
+export const mkAttrsWithPos = (
+  attrs: NixAttrs,
+  positions: Record<string, string>,
+  dyns?: { dynKeys: NixValue[]; dynVals: NixValue[]; dynSpans: string[] }
+): NixAttrs => {
+  if (dyns) {
+    const len = dyns.dynKeys.length;
+    for (let i = 0; i < len; i++) {
+      const key = force(dyns.dynKeys[i]);
+      if (key === null) {
+        continue;
+      }
+      const str = forceStringNoCtx(key);
+      attrs[str] = dyns.dynVals[i];
+      positions[str] = dyns.dynSpans[i];
+    }
+  }
+
+  if (Object.keys(positions).length > 0) {
+    Object.defineProperty(attrs, ATTR_POSITIONS, {
+      value: positions,
+      enumerable: false,
+      writable: false,
+    });
+  }
+
+  return attrs;
+};
+
+export { ATTR_POSITIONS };

 /**
 * Interface for lazy thunk values
--- a/nix-js/runtime-ts/src/types/global.d.ts
+++ b/nix-js/runtime-ts/src/types/global.d.ts
@@ -38,8 +38,11 @@ declare global {
        function op_resolve_path(currentDir: string, path: string): string;
        function op_import(path: string): string;
        function op_read_file(path: string): string;
+        function op_read_file_type(path: string): string;
+        function op_read_dir(path: string): Record<string, string>;
        function op_path_exists(path: string): boolean;
        function op_sha256_hex(data: string): string;
+        function op_decode_span(span: string): { file: string | null; line: number | null; column: number | null };
        function op_make_store_path(ty: string, hash_hex: string, name: string): string;
        function op_output_path_name(drv_name: string, output_name: string): string;
        function op_make_fixed_output_path(
--- a/nix-js/src/codegen.rs
+++ b/nix-js/src/codegen.rs
@@ -40,6 +40,7 @@ pub(crate) trait CodegenContext {
    fn get_current_dir(&self) -> &Path;
    fn get_store_dir(&self) -> &str;
    fn get_current_source_id(&self) -> usize;
+    fn get_current_source(&self) -> crate::error::Source;
 }

 trait EscapeQuote {
@@ -117,9 +118,19 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Ir {
            Ir::Arg(x) => format!("arg{}", x.inner.0),
            Ir::Let(x) => x.compile(ctx),
            Ir::Select(x) => x.compile(ctx),
-            &Ir::Thunk(Thunk { inner: expr_id, .. }) => {
+            &Ir::Thunk(Thunk {
+                inner: expr_id,
+                span,
+            }) => {
                let inner = ctx.get_ir(expr_id).compile(ctx);
-                format!("Nix.createThunk(()=>({}),\"expr{}\")", inner, expr_id.0)
+                format!(
+                    "Nix.createThunk(()=>({}),\"expr{} {}:{}:{}\")",
+                    inner,
+                    expr_id.0,
+                    ctx.get_current_source().get_name(),
+                    usize::from(span.start()),
+                    usize::from(span.end())
+                )
            }
            &Ir::ExprRef(ExprRef { inner: expr_id, .. }) => {
                format!("expr{}", expr_id.0)
@@ -160,6 +171,10 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Ir {
                    )
                }
            }
+            Ir::CurPos(cur_pos) => {
+                let span_str = encode_span(cur_pos.span, ctx);
+                format!("Nix.mkPos({})", span_str)
+            }
        }
    }
 }
@@ -316,8 +331,8 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Select {
            .attrpath
            .iter()
            .map(|attr| match attr {
-                Attr::Str(sym) => ctx.get_sym(*sym).escape_quote(),
-                Attr::Dynamic(expr_id) => ctx.get_ir(*expr_id).compile(ctx),
+                Attr::Str(sym, _) => ctx.get_sym(*sym).escape_quote(),
+                Attr::Dynamic(expr_id, _) => ctx.get_ir(*expr_id).compile(ctx),
            })
            .join(",");
        let span_str = encode_span(self.span, ctx);
@@ -335,9 +350,10 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Select {
 impl<Ctx: CodegenContext> Compile<Ctx> for AttrSet {
    fn compile(&self, ctx: &Ctx) -> String {
        let mut attrs = Vec::new();
+        let mut attr_positions = Vec::new();
        let stack_trace_enabled = std::env::var("NIX_JS_STACK_TRACE").is_ok();

-        for (&sym, &expr) in &self.stcs {
+        for (&sym, &(expr, attr_span)) in &self.stcs {
            let key = ctx.get_sym(sym);
            let value_code = ctx.get_ir(expr).compile(ctx);

@@ -351,27 +367,51 @@ impl<Ctx: CodegenContext> Compile<Ctx> for AttrSet {
                value_code
            };
            attrs.push(format!("{}:{}", key.escape_quote(), value));
+
+            let attr_pos_str = encode_span(attr_span, ctx);
+            attr_positions.push(format!("{}:{}", key.escape_quote(), attr_pos_str));
        }

-        // FIXME: duplicated key
-        for (key_expr, value_expr) in &self.dyns {
-            let key = ctx.get_ir(*key_expr).compile(ctx);
-            let value_code = ctx.get_ir(*value_expr).compile(ctx);
-
-            let value = if stack_trace_enabled {
-                let value_span = encode_span(ctx.get_ir(*value_expr).span(), ctx);
+        if !self.dyns.is_empty() {
+            let (keys, vals, dyn_spans) = self
+                .dyns
+                .iter()
+                .map(|(key, val, attr_span)| {
+                    let key = ctx.get_ir(*key).compile(ctx);
+                    let val_expr = ctx.get_ir(*val);
+                    let val = val_expr.compile(ctx);
+                    let span = val_expr.span();
+                    let val = if stack_trace_enabled {
+                        let span = encode_span(span, ctx);
                        format!(
                            "Nix.withContext(\"while evaluating a dynamic attribute\",{},()=>({}))",
-                    value_span, value_code
+                            span, val
                        )
                    } else {
-                value_code
+                        val
                    };
-            attrs.push(format!("[{}]:{}", key, value));
-        }
-
+                    let dyn_span_str = encode_span(*attr_span, ctx);
+                    (key, val, dyn_span_str)
+                })
+                .multiunzip::<(Vec<_>, Vec<_>, Vec<_>)>();
+            format!(
+                "Nix.mkAttrsWithPos({{{}}},{{{}}},{{dynKeys:[{}],dynVals:[{}],dynSpans:[{}]}})",
+                attrs.join(","),
+                attr_positions.join(","),
+                keys.join(","),
+                vals.join(","),
+                dyn_spans.join(",")
+            )
+        } else if !attr_positions.is_empty() {
+            format!(
+                "Nix.mkAttrsWithPos({{{}}},{{{}}})",
+                attrs.join(","),
+                attr_positions.join(",")
+            )
+        } else {
            format!("{{{}}}", attrs.join(","))
        }
+    }
 }

 impl<Ctx: CodegenContext> Compile<Ctx> for List {
@@ -431,8 +471,8 @@ impl<Ctx: CodegenContext> Compile<Ctx> for HasAttr {
            .rhs
            .iter()
            .map(|attr| match attr {
-                Attr::Str(sym) => ctx.get_sym(*sym).escape_quote(),
-                Attr::Dynamic(expr_id) => ctx.get_ir(*expr_id).compile(ctx),
+                Attr::Str(sym, _) => ctx.get_sym(*sym).escape_quote(),
+                Attr::Dynamic(expr_id, _) => ctx.get_ir(*expr_id).compile(ctx),
            })
            .join(",");
        format!("Nix.hasAttr({lhs},[{attrpath}])")
--- a/nix-js/src/context.rs
+++ b/nix-js/src/context.rs
@@ -11,51 +11,11 @@ use crate::codegen::{CodegenContext, compile};
 use crate::error::{Error, Result, Source};
 use crate::ir::{
    Arg, ArgId, Bool, Builtin, Downgrade as _, DowngradeContext, ExprId, ExprRef, Ir, Null, SymId,
-    ToIr as _, synthetic_span,
+    Thunk, ToIr as _, synthetic_span,
 };
 use crate::runtime::{Runtime, RuntimeContext};
-use crate::store::{StoreBackend, StoreConfig};
+use crate::store::{Store, StoreBackend, StoreConfig};
 use crate::value::Value;
-use std::sync::Arc;
-
-mod private {
-    use super::*;
-    use std::ptr::NonNull;
-
-    pub struct CtxPtr(NonNull<Ctx>);
-    impl CtxPtr {
-        pub fn new(ctx: &mut Ctx) -> Self {
-            unsafe { CtxPtr(NonNull::new_unchecked(ctx)) }
-        }
-        fn as_ref(&self) -> &Ctx {
-            // SAFETY: This is safe since inner `NonNull<Ctx>` is obtained from `&mut Ctx`
-            unsafe { self.0.as_ref() }
-        }
-        fn as_mut(&mut self) -> &mut Ctx {
-            // SAFETY: This is safe since inner `NonNull<Ctx>` is obtained from `&mut Ctx`
-            unsafe { self.0.as_mut() }
-        }
-    }
-
-    impl RuntimeContext for CtxPtr {
-        fn get_current_dir(&self) -> &Path {
-            self.as_ref().get_current_dir()
-        }
-        fn add_source(&mut self, source: Source) {
-            self.as_mut().sources.push(source);
-        }
-        fn compile_code(&mut self, source: Source) -> Result<String> {
-            self.as_mut().compile_code(source)
-        }
-        fn get_current_source(&self) -> Source {
-            self.as_ref().get_current_source()
-        }
-        fn get_source(&self, id: usize) -> Source {
-            self.as_ref().get_source(id)
-        }
-    }
-}
-use private::CtxPtr;

 #[derive(Debug)]
 pub(crate) struct SccInfo {
@@ -65,7 +25,7 @@ pub(crate) struct SccInfo {

 pub struct Context {
    ctx: Ctx,
-    runtime: Runtime<CtxPtr>,
+    runtime: Runtime<Ctx>,
 }

 impl Context {
@@ -82,14 +42,9 @@ impl Context {
        tracing::debug!("Compiling code");
        let code = self.compile_code(source)?;

-        self.runtime
-            .op_state()
-            .borrow_mut()
-            .put(self.ctx.store.clone());
-
        tracing::debug!("Executing JavaScript");
        self.runtime
-            .eval(format!("Nix.force({code})"), CtxPtr::new(&mut self.ctx))
+            .eval(format!("Nix.force({code})"), &mut self.ctx)
    }

    pub fn compile_code(&mut self, source: Source) -> Result<String> {
@@ -98,7 +53,7 @@ impl Context {

    #[allow(dead_code)]
    pub(crate) fn eval_js(&mut self, code: String) -> Result<Value> {
-        self.runtime.eval(code, CtxPtr::new(&mut self.ctx))
+        self.runtime.eval(code, &mut self.ctx)
    }

    pub fn get_store_dir(&self) -> &str {
@@ -111,7 +66,7 @@ pub(crate) struct Ctx {
    symbols: DefaultStringInterner,
    global: NonNull<HashMap<SymId, ExprId>>,
    sources: Vec<Source>,
-    store: Arc<StoreBackend>,
+    store: StoreBackend,
 }

 impl Ctx {
@@ -200,7 +155,7 @@ impl Ctx {
        }

        let config = StoreConfig::from_env();
-        let store = Arc::new(StoreBackend::new(config)?);
+        let store = StoreBackend::new(config)?;

        Ok(Self {
            symbols,
@@ -210,9 +165,7 @@ impl Ctx {
            store,
        })
    }
-}

-impl Ctx {
    pub(crate) fn downgrade_ctx<'a>(&'a mut self) -> DowngradeCtx<'a> {
        let global_ref = unsafe { self.global.as_ref() };
        DowngradeCtx::new(self, global_ref)
@@ -277,11 +230,32 @@ impl CodegenContext for Ctx {
            .checked_sub(1)
            .expect("current_source not set")
    }
+    fn get_current_source(&self) -> crate::error::Source {
+        self.sources.last().expect("current_source not set").clone()
+    }
    fn get_store_dir(&self) -> &str {
        self.store.as_store().get_store_dir()
    }
 }

+impl RuntimeContext for Ctx {
+    fn get_current_dir(&self) -> &Path {
+        self.get_current_dir()
+    }
+    fn add_source(&mut self, source: Source) {
+        self.sources.push(source);
+    }
+    fn compile_code(&mut self, source: Source) -> Result<String> {
+        self.compile_code(source)
+    }
+    fn get_source(&self, id: usize) -> Source {
+        self.get_source(id)
+    }
+    fn get_store(&self) -> &dyn Store {
+        self.store.as_store()
+    }
+}
+
 struct DependencyTracker {
    graph: DiGraphMap<ExprId, ()>,
    current_binding: Option<ExprId>,
@@ -351,6 +325,38 @@ impl DowngradeContext for DowngradeCtx<'_> {
        ExprId(self.ctx.irs.len() + self.irs.len() - 1)
    }

+    fn get_ir(&self, id: ExprId) -> &Ir {
+        if id.0 < self.ctx.irs.len() {
+            self.ctx.irs.get(id.0).expect("unreachable")
+        } else {
+            self.irs
+                .get(id.0 - self.ctx.irs.len())
+                .expect("ExprId out of bounds")
+                .as_ref()
+                .expect("maybe_thunk called on an extracted expr")
+        }
+    }
+
+    fn maybe_thunk(&mut self, id: ExprId) -> ExprId {
+        let ir = self.get_ir(id);
+        match ir {
+            Ir::Builtin(_)
+            | Ir::Builtins(_)
+            | Ir::Int(_)
+            | Ir::Float(_)
+            | Ir::Bool(_)
+            | Ir::Null(_)
+            | Ir::Str(_) => id,
+            _ => self.new_expr(
+                Thunk {
+                    inner: id,
+                    span: ir.span(),
+                }
+                .to_ir(),
+            ),
+        }
+    }
+
    fn new_sym(&mut self, sym: String) -> SymId {
        self.ctx.symbols.get_or_intern(sym)
    }
@@ -435,20 +441,22 @@ impl DowngradeContext for DowngradeCtx<'_> {
            use crate::ir::{Attr, Select};
            let select = Select {
                expr: namespace,
-                attrpath: vec![Attr::Str(sym)],
+                attrpath: vec![Attr::Str(sym, synthetic_span())],
                default: result, // Link to outer With or None
                span,
            };
            result = Some(self.new_expr(select.to_ir()));
        }
        result.ok_or_else(|| {
-            Error::downgrade_error(format!("'{}' not found", self.get_sym(sym)))
-                .with_span(span)
-                .with_source(self.get_current_source())
+            Error::downgrade_error(
+                format!("'{}' not found", self.get_sym(sym)),
+                self.get_current_source(),
+                span,
+            )
        })
    }

-    fn extract_expr(&mut self, id: ExprId) -> Ir {
+    fn extract_ir(&mut self, id: ExprId) -> Ir {
        let local_id = id.0 - self.ctx.irs.len();
        self.irs
            .get_mut(local_id)
@@ -457,7 +465,7 @@ impl DowngradeContext for DowngradeCtx<'_> {
            .expect("extract_expr called on an already extracted expr")
    }

-    fn replace_expr(&mut self, id: ExprId, expr: Ir) {
+    fn replace_ir(&mut self, id: ExprId, expr: Ir) {
        let local_id = id.0 - self.ctx.irs.len();
        let _ = self
            .irs
--- a/nix-js/src/error.rs
+++ b/nix-js/src/error.rs
@@ -1,11 +1,15 @@
+#![allow(unused_assignments)]
+
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+
+use deno_core::error::JsError;
+use deno_error::JsErrorClass as _;
+use itertools::Itertools as _;
 use miette::{Diagnostic, NamedSource, SourceSpan};
-use std::{
-    path::{Path, PathBuf},
-    sync::Arc,
-};
 use thiserror::Error;

-use crate::{context::Ctx, runtime::RuntimeContext};
+use crate::runtime::RuntimeContext;

 pub type Result<T> = core::result::Result<T, Box<Error>>;

@@ -34,11 +38,7 @@ impl TryFrom<&str> for Source {

 impl From<Source> for NamedSource<Arc<str>> {
    fn from(value: Source) -> Self {
-        let name = match value.ty {
-            SourceType::Eval(_) => "«eval»".into(),
-            SourceType::Repl(_) => "«repl»".into(),
-            SourceType::File(path) => path.as_os_str().to_string_lossy().to_string(),
-        };
+        let name = value.get_name();
        NamedSource::new(name, value.src.clone())
    }
 }
@@ -74,6 +74,14 @@ impl Source {
                .expect("source file must have a parent dir"),
        }
    }
+
+    pub fn get_name(&self) -> String {
+        match &self.ty {
+            SourceType::Eval(_) => "«eval»".into(),
+            SourceType::Repl(_) => "«repl»".into(),
+            SourceType::File(path) => path.as_os_str().to_string_lossy().to_string(),
+        }
+    }
 }

 #[derive(Error, Debug, Diagnostic)]
@@ -108,6 +116,8 @@ pub enum Error {
        message: String,
        #[help]
        js_backtrace: Option<String>,
+        #[related]
+        stack_trace: Vec<StackFrame>,
    },

    #[error("Internal error: {message}")]
@@ -133,10 +143,10 @@ impl Error {
        .into()
    }

-    pub fn downgrade_error(msg: String) -> Box<Self> {
+    pub fn downgrade_error(msg: String, src: Source, span: rnix::TextRange) -> Box<Self> {
        Error::DowngradeError {
-            src: None,
-            span: None,
+            src: Some(src.into()),
+            span: Some(text_range_to_source_span(span)),
            message: msg,
        }
        .into()
@@ -148,6 +158,7 @@ impl Error {
            span: None,
            message: msg,
            js_backtrace: backtrace,
+            stack_trace: Vec::new(),
        }
        .into()
    }
@@ -192,14 +203,72 @@ pub fn text_range_to_source_span(range: rnix::TextRange) -> SourceSpan {
 }

 /// Stack frame types from Nix evaluation
-#[derive(Debug, Clone)]
-pub(crate) struct NixStackFrame {
-    pub span: rnix::TextRange,
+#[derive(Debug, Clone, Error, Diagnostic)]
+#[error("{message}")]
+pub struct StackFrame {
+    #[label]
+    pub span: SourceSpan,
+    #[help]
    pub message: String,
-    pub source: Source,
+    #[source_code]
+    pub src: NamedSource<Arc<str>>,
 }

-pub(crate) fn parse_nix_stack(stack: &str, ctx: &impl RuntimeContext) -> Vec<NixStackFrame> {
+const MAX_STACK_FRAMES: usize = 10;
+const FRAMES_AT_START: usize = 5;
+const FRAMES_AT_END: usize = 5;
+
+pub(crate) fn parse_js_error(error: Box<JsError>, ctx: &impl RuntimeContext) -> Error {
+    let (span, src, frames) = if let Some(stack) = &error.stack {
+        let mut frames = parse_frames(stack, ctx);
+
+        if let Some(last_frame) = frames.pop() {
+            (
+                Some(text_range_to_source_span(last_frame.span)),
+                Some(last_frame.src.into()),
+                frames,
+            )
+        } else {
+            (None, None, frames)
+        }
+    } else {
+        (None, None, Vec::new())
+    };
+    let stack_trace = truncate_stack_trace(frames);
+    let message = error.get_message().to_string();
+    let js_backtrace = error.stack.map(|stack| {
+        stack
+            .lines()
+            .filter(|line| !line.starts_with("NIX_STACK_FRAME:"))
+            .join("\n")
+    });
+
+    Error::EvalError {
+        src,
+        span,
+        message,
+        js_backtrace,
+        stack_trace,
+    }
+}
+
+struct NixStackFrame {
+    span: rnix::TextRange,
+    message: String,
+    src: Source,
+}
+
+impl From<NixStackFrame> for StackFrame {
+    fn from(NixStackFrame { span, message, src }: NixStackFrame) -> Self {
+        StackFrame {
+            span: text_range_to_source_span(span),
+            message,
+            src: src.into(),
+        }
+    }
+}
+
+fn parse_frames(stack: &str, ctx: &impl RuntimeContext) -> Vec<NixStackFrame> {
    let mut frames = Vec::new();

    for line in stack.lines() {
@@ -213,7 +282,7 @@ pub(crate) fn parse_nix_stack(stack: &str, ctx: &impl RuntimeContext) -> Vec<Nix
            continue;
        }

-        let source = match parts[0].parse() {
+        let src = match parts[0].parse() {
            Ok(id) => ctx.get_source(id),
            Err(_) => continue,
        };
@@ -236,11 +305,7 @@ pub(crate) fn parse_nix_stack(stack: &str, ctx: &impl RuntimeContext) -> Vec<Nix
            }
        };

-        frames.push(NixStackFrame {
-            span,
-            message,
-            source,
-        });
+        frames.push(NixStackFrame { span, message, src });
    }

    // Deduplicate consecutive identical frames
@@ -248,3 +313,34 @@ pub(crate) fn parse_nix_stack(stack: &str, ctx: &impl RuntimeContext) -> Vec<Nix

    frames
 }
+
+fn truncate_stack_trace(frames: Vec<NixStackFrame>) -> Vec<StackFrame> {
+    let reversed: Vec<_> = frames.into_iter().rev().collect();
+    let total = reversed.len();
+
+    if total <= MAX_STACK_FRAMES {
+        return reversed.into_iter().map(Into::into).collect();
+    }
+
+    let omitted_count = total - FRAMES_AT_START - FRAMES_AT_END;
+
+    reversed
+        .into_iter()
+        .enumerate()
+        .filter_map(|(i, frame)| {
+            if i < FRAMES_AT_START {
+                Some(frame.into())
+            } else if i == FRAMES_AT_START {
+                Some(StackFrame {
+                    span: text_range_to_source_span(frame.span),
+                    message: format!("... ({} more frames omitted)", omitted_count),
+                    src: frame.src.into(),
+                })
+            } else if i >= total - FRAMES_AT_END {
+                Some(frame.into())
+            } else {
+                None
+            }
+        })
+        .collect()
+}
--- a/nix-js/src/fetcher.rs
+++ b/nix-js/src/fetcher.rs
@@ -3,6 +3,9 @@ use deno_core::op2;
 use serde::Serialize;
 use tracing::{debug, info, warn};

+use crate::runtime::OpStateExt;
+use crate::runtime::RuntimeContext;
+
 mod archive;
 pub(crate) mod cache;
 mod download;
@@ -53,16 +56,13 @@ pub struct FetchHgResult {

 #[op2]
 #[serde]
-pub fn op_fetch_url(
+pub fn op_fetch_url<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] url: String,
    #[string] expected_hash: Option<String>,
    #[string] name: Option<String>,
    executable: bool,
 ) -> Result<FetchUrlResult, NixError> {
-    use crate::store::StoreBackend;
-    use std::sync::Arc;
-
    let _span = tracing::info_span!("op_fetch_url", url = %url).entered();
    info!("fetchurl started");

@@ -128,9 +128,9 @@ pub fn op_fetch_url(
        }
    }

-    let store = state.borrow::<Arc<StoreBackend>>();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();
    let store_path = store
-        .as_store()
        .add_to_store(&file_name, &data, false, vec![])
        .map_err(|e| NixError::from(e.to_string()))?;

@@ -160,16 +160,13 @@ pub fn op_fetch_url(

 #[op2]
 #[serde]
-pub fn op_fetch_tarball(
+pub fn op_fetch_tarball<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] url: String,
    #[string] expected_hash: Option<String>,
    #[string] expected_nar_hash: Option<String>,
    #[string] name: Option<String>,
 ) -> Result<FetchTarballResult, NixError> {
-    use crate::store::StoreBackend;
-    use std::sync::Arc;
-
    let _span = tracing::info_span!("op_fetch_tarball", url = %url).entered();
    info!("fetchTarball started");

@@ -264,9 +261,9 @@ pub fn op_fetch_tarball(
    }

    info!("Adding to store");
-    let store = state.borrow::<Arc<StoreBackend>>();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();
    let store_path = store
-        .as_store()
        .add_to_store_from_path(&dir_name, &extracted_path, vec![])
        .map_err(|e| NixError::from(e.to_string()))?;

@@ -292,7 +289,7 @@ pub fn op_fetch_tarball(

 #[op2]
 #[serde]
-pub fn op_fetch_git(
+pub fn op_fetch_git<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] url: String,
    #[string] git_ref: Option<String>,
@@ -302,19 +299,17 @@ pub fn op_fetch_git(
    all_refs: bool,
    #[string] name: Option<String>,
 ) -> Result<FetchGitResult, NixError> {
-    use crate::store::StoreBackend;
-    use std::sync::Arc;
-
    let _span = tracing::info_span!("op_fetch_git", url = %url).entered();
    info!("fetchGit started");
    let cache = FetcherCache::new().map_err(|e| NixError::from(e.to_string()))?;
    let dir_name = name.unwrap_or_else(|| "source".to_string());

-    let store = state.borrow::<Arc<StoreBackend>>();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();

    git::fetch_git(
        &cache,
-        store.as_store(),
+        store,
        &url,
        git_ref.as_deref(),
        rev.as_deref(),
@@ -377,11 +372,11 @@ fn base64_decode(input: &str) -> Result<Vec<u8>, String> {
    Ok(output)
 }

-pub fn register_ops() -> Vec<deno_core::OpDecl> {
+pub fn register_ops<Ctx: RuntimeContext>() -> Vec<deno_core::OpDecl> {
    vec![
-        op_fetch_url(),
-        op_fetch_tarball(),
-        op_fetch_git(),
+        op_fetch_url::<Ctx>(),
+        op_fetch_tarball::<Ctx>(),
+        op_fetch_git::<Ctx>(),
        op_fetch_hg(),
    ]
 }
--- a/nix-js/src/fetcher/metadata_cache.rs
+++ b/nix-js/src/fetcher/metadata_cache.rs
@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 use rusqlite::{Connection, OptionalExtension, params};
 use serde::{Deserialize, Serialize};
 use std::path::PathBuf;
--- a/nix-js/src/ir.rs
+++ b/nix-js/src/ir.rs
@@ -1,5 +1,5 @@
 use derive_more::{IsVariant, TryUnwrap, Unwrap};
-use hashbrown::{HashMap, HashSet};
+use hashbrown::HashMap;
 use rnix::{TextRange, ast};
 use string_interner::symbol::SymbolU32;

@@ -22,13 +22,15 @@ pub trait DowngradeContext {

    fn new_expr(&mut self, expr: Ir) -> ExprId;
    fn new_arg(&mut self, span: TextRange) -> ExprId;
+    fn maybe_thunk(&mut self, id: ExprId) -> ExprId;

    fn new_sym(&mut self, sym: String) -> SymId;
    fn get_sym(&self, id: SymId) -> &str;
    fn lookup(&mut self, sym: SymId, span: TextRange) -> Result<ExprId>;

-    fn extract_expr(&mut self, id: ExprId) -> Ir;
-    fn replace_expr(&mut self, id: ExprId, expr: Ir);
+    fn get_ir(&self, id: ExprId) -> &Ir;
+    fn extract_ir(&mut self, id: ExprId) -> Ir;
+    fn replace_ir(&mut self, id: ExprId, expr: Ir);
    fn reserve_slots(&mut self, slots: usize) -> impl Iterator<Item = ExprId> + Clone + use<Self>;
    fn get_current_source(&self) -> Source;

@@ -57,7 +59,7 @@ ir! {
    Bool(bool),
    Null,
    Str { pub val: String },
-    AttrSet { pub stcs: HashMap<SymId, ExprId>, pub dyns: Vec<(ExprId, ExprId)> },
+    AttrSet { pub stcs: HashMap<SymId, (ExprId, rnix::TextRange)>, pub dyns: Vec<(ExprId, ExprId, rnix::TextRange)> },
    List { pub items: Vec<ExprId> },

    HasAttr { pub lhs: ExprId, pub rhs: Vec<Attr> },
@@ -76,6 +78,7 @@ ir! {
    Thunk(ExprId),
    Builtins,
    Builtin(SymId),
+    CurPos,
 }

 impl Ir {
@@ -104,6 +107,7 @@ impl Ir {
            Ir::Thunk(t) => t.span,
            Ir::Builtins(b) => b.span,
            Ir::Builtin(b) => b.span,
+            Ir::CurPos(c) => c.span,
        }
    }
 }
@@ -119,11 +123,11 @@ impl AttrSet {
        if let Some(attr) = path.next() {
            // If the path is not yet exhausted, we need to recurse deeper.
            match attr {
-                Attr::Str(ident) => {
+                Attr::Str(ident, span) => {
                    // If the next attribute is a static string.
-                    if let Some(&id) = self.stcs.get(&ident) {
+                    if let Some(&(id, _)) = self.stcs.get(&ident) {
                        // If a sub-attrset already exists, recurse into it.
-                        let mut ir = ctx.extract_expr(id);
+                        let mut ir = ctx.extract_ir(id);
                        let result = ir
                            .as_mut()
                            .try_unwrap_attr_set()
@@ -131,11 +135,14 @@ impl AttrSet {
                                // This path segment exists but is not an attrset, which is an error.
                                Error::downgrade_error(format!(
                                    "attribute '{}' already defined but is not an attribute set",
-                                    format_symbol(ctx.get_sym(ident))
-                                ))
+                                    format_symbol(ctx.get_sym(ident)),
+                                ),
+                                    ctx.get_current_source(),
+                                    span
+                                )
                            })
                            .and_then(|attrs| attrs._insert(path, name, value, ctx));
-                        ctx.replace_expr(id, ir);
+                        ctx.replace_ir(id, ir);
                        result?;
                    } else {
                        // Create a new sub-attrset because this path doesn't exist yet.
@@ -143,41 +150,45 @@ impl AttrSet {
                        let mut attrs = AttrSet {
                            stcs: Default::default(),
                            dyns: Default::default(),
-                            span: synthetic_span(),
+                            span,
                        };
                        attrs._insert(path, name, value, ctx)?;
-                        let attrs = ctx.new_expr(attrs.to_ir());
-                        self.stcs.insert(ident, attrs);
+                        let attrs_expr = ctx.new_expr(attrs.to_ir());
+                        self.stcs.insert(ident, (attrs_expr, span));
                    }
                    Ok(())
                }
-                Attr::Dynamic(dynamic) => {
+                Attr::Dynamic(dynamic, span) => {
                    // If the next attribute is a dynamic expression, we must create a new sub-attrset.
                    // We cannot merge with existing dynamic attributes at this stage.
                    // FIXME: span
                    let mut attrs = AttrSet {
                        stcs: Default::default(),
                        dyns: Default::default(),
-                        span: synthetic_span(),
+                        span,
                    };
                    attrs._insert(path, name, value, ctx)?;
-                    self.dyns.push((dynamic, ctx.new_expr(attrs.to_ir())));
+                    self.dyns.push((dynamic, ctx.new_expr(attrs.to_ir()), span));
                    Ok(())
                }
            }
        } else {
            // This is the final attribute in the path, so insert the value here.
            match name {
-                Attr::Str(ident) => {
-                    if self.stcs.insert(ident, value).is_some() {
-                        return Err(Error::downgrade_error(format!(
+                Attr::Str(ident, span) => {
+                    if self.stcs.insert(ident, (value, span)).is_some() {
+                        return Err(Error::downgrade_error(
+                            format!(
                                "attribute '{}' already defined",
-                            format_symbol(ctx.get_sym(ident))
-                        )));
+                                format_symbol(ctx.get_sym(ident)),
+                            ),
+                            ctx.get_current_source(),
+                            span,
+                        ));
                    }
                }
-                Attr::Dynamic(dynamic) => {
-                    self.dyns.push((dynamic, value));
+                Attr::Dynamic(dynamic, span) => {
+                    self.dyns.push((dynamic, value, span));
                }
            }
            Ok(())
@@ -214,10 +225,10 @@ pub struct ArgId(pub usize);
 pub enum Attr {
    /// A dynamic attribute key, which is an expression that must evaluate to a string.
    /// Example: `attrs.${key}`
-    Dynamic(ExprId),
+    Dynamic(ExprId, TextRange),
    /// A static attribute key.
    /// Example: `attrs.key`
-    Str(SymId),
+    Str(SymId, TextRange),
 }

 /// The kinds of binary operations supported in Nix.
--- a/nix-js/src/ir/downgrade.rs
+++ b/nix-js/src/ir/downgrade.rs
@@ -19,9 +19,11 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for Expr {
            Assert(assert) => assert.downgrade(ctx),
            Error(error) => {
                let span = error.syntax().text_range();
-                Err(self::Error::downgrade_error(error.to_string())
-                    .with_span(span)
-                    .with_source(ctx.get_current_source()))
+                Err(self::Error::downgrade_error(
+                    error.to_string(),
+                    ctx.get_current_source(),
+                    span,
+                ))
            }
            IfElse(ifelse) => ifelse.downgrade(ctx),
            Select(select) => select.downgrade(ctx),
@@ -101,7 +103,41 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Path {
            .collect::<Result<Vec<_>>>()?;

        let expr = if parts.len() == 1 {
-            parts.into_iter().next().unwrap()
+            let part = parts.into_iter().next().unwrap();
+            if let &Ir::Str(Str { ref val, span }) = ctx.get_ir(part)
+                && let Some(path) = val.strip_prefix("<").map(|path| &path[..path.len() - 1])
+            {
+                ctx.replace_ir(
+                    part,
+                    Str {
+                        val: path.to_string(),
+                        span,
+                    }
+                    .to_ir(),
+                );
+                let sym = ctx.new_sym("findFile".into());
+                let find_file = ctx.new_expr(Builtin { inner: sym, span }.to_ir());
+                let sym = ctx.new_sym("nixPath".into());
+                let nix_path = ctx.new_expr(Builtin { inner: sym, span }.to_ir());
+                let call = ctx.new_expr(
+                    Call {
+                        func: find_file,
+                        arg: nix_path,
+                        span,
+                    }
+                    .to_ir(),
+                );
+                return Ok(ctx.new_expr(
+                    Call {
+                        func: call,
+                        arg: part,
+                        span,
+                    }
+                    .to_ir(),
+                ));
+            } else {
+                part
+            }
        } else {
            ctx.new_expr(ConcatStrings { parts, span }.to_ir())
        };
@@ -121,7 +157,8 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Str {
            .map(|part| match part {
                ast::InterpolPart::Literal(lit) => Ok(ctx.new_expr(Str { val: lit, span }.to_ir())),
                ast::InterpolPart::Interpolation(interpol) => {
-                    interpol.expr().unwrap().downgrade(ctx)
+                    let inner = interpol.expr().unwrap().downgrade(ctx)?;
+                    Ok(ctx.new_expr(Thunk { inner, span }.to_ir()))
                }
            })
            .collect::<Result<Vec<_>>>()?;
@@ -159,9 +196,15 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Literal {

 impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Ident {
    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let sym = self.ident_token().unwrap().to_string();
-        let sym = ctx.new_sym(sym);
-        ctx.lookup(sym, self.syntax().text_range())
+        let text = self.ident_token().unwrap().to_string();
+        let span = self.syntax().text_range();
+
+        if text == "__curPos" {
+            return Ok(ctx.new_expr(CurPos { span }.to_ir()));
+        }
+
+        let sym = ctx.new_sym(text);
+        ctx.lookup(sym, span)
    }
 }

@@ -188,7 +231,7 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::AttrSet {
            for sym in binding_keys {
                // FIXME: span
                let expr = ctx.lookup(*sym, synthetic_span())?;
-                attrs.stcs.insert(*sym, expr);
+                attrs.stcs.insert(*sym, (expr, synthetic_span()));
            }

            Ok(ctx.new_expr(attrs.to_ir()))
@@ -210,7 +253,10 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::List {
    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
        let items = self
            .items()
-            .map(|item| maybe_thunk(item, ctx))
+            .map(|item| {
+                let id = item.downgrade(ctx)?;
+                Ok(ctx.maybe_thunk(id))
+            })
            .collect::<Result<_>>()?;
        let span = self.syntax().text_range();
        Ok(ctx.new_expr(List { items, span }.to_ir()))
@@ -307,7 +353,7 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::LegacyLet {
            for sym in binding_keys {
                // FIXME: span
                let expr = ctx.lookup(sym, synthetic_span())?;
-                attrs.stcs.insert(sym, expr);
+                attrs.stcs.insert(sym, (expr, synthetic_span()));
            }

            Result::Ok(ctx.new_expr(attrs.to_ir()))
@@ -316,7 +362,7 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::LegacyLet {
        let body_sym = ctx.new_sym("body".to_string());
        let select = Select {
            expr: attrset_expr,
-            attrpath: vec![Attr::Str(body_sym)],
+            attrpath: vec![Attr::Str(body_sym, synthetic_span())],
            default: None,
            span,
        };
@@ -393,14 +439,9 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Lambda {
                    scc_info,
                    required,
                    optional,
-                } = downgrade_pattern_bindings(
-                    pat_entries,
-                    alias,
-                    arg,
-                    ellipsis,
-                    ctx,
-                    |ctx, _| self.body().unwrap().downgrade(ctx),
-                )?;
+                } = downgrade_pattern_bindings(pat_entries, alias, arg, ctx, |ctx, _| {
+                    self.body().unwrap().downgrade(ctx)
+                })?;

                param = Some(Param {
                    required,
@@ -439,7 +480,8 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Lambda {
 impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Apply {
    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
        let func = self.lambda().unwrap().downgrade(ctx)?;
-        let arg = maybe_thunk(self.argument().unwrap(), ctx)?;
+        let arg = self.argument().unwrap().downgrade(ctx)?;
+        let arg = ctx.maybe_thunk(arg);
        let span = self.syntax().text_range();
        Ok(ctx.new_expr(Call { func, arg, span }.to_ir()))
    }
--- a/nix-js/src/ir/span_utils.rs
+++ b/nix-js/src/ir/span_utils.rs
@@ -1,3 +1,5 @@
+#![allow(unused)]
+
 use rnix::TextRange;

 pub fn merge_spans(spans: impl IntoIterator<Item = TextRange>) -> TextRange {
@@ -11,10 +13,6 @@ pub fn merge_spans(spans: impl IntoIterator<Item = TextRange>) -> TextRange {
    })
 }

-pub fn point_span() -> TextRange {
-    TextRange::new(0.into(), 0.into())
-}
-
 pub fn synthetic_span() -> TextRange {
    TextRange::new(0.into(), 0.into())
 }
--- a/nix-js/src/ir/utils.rs
+++ b/nix-js/src/ir/utils.rs
@@ -13,57 +13,6 @@ use crate::value::format_symbol;

 use super::*;

-pub fn maybe_thunk(mut expr: ast::Expr, ctx: &mut impl DowngradeContext) -> Result<ExprId> {
-    use ast::Expr::*;
-    let expr = loop {
-        expr = match expr {
-            Paren(paren) => paren.expr().unwrap(),
-            Root(root) => root.expr().unwrap(),
-            expr => break expr,
-        }
-    };
-    match expr {
-        Error(error) => {
-            let span = error.syntax().text_range();
-            return Err(self::Error::downgrade_error(error.to_string())
-                .with_span(span)
-                .with_source(ctx.get_current_source()));
-        }
-        Ident(ident) => return ident.downgrade(ctx),
-        Literal(lit) => return lit.downgrade(ctx),
-        Str(str) => return str.downgrade(ctx),
-        Path(path) => return path.downgrade(ctx),
-
-        _ => (),
-    }
-    let id = match expr {
-        Apply(apply) => apply.downgrade(ctx),
-        Assert(assert) => assert.downgrade(ctx),
-        IfElse(ifelse) => ifelse.downgrade(ctx),
-        Select(select) => select.downgrade(ctx),
-        Lambda(lambda) => lambda.downgrade(ctx),
-        LegacyLet(let_) => let_.downgrade(ctx),
-        LetIn(letin) => letin.downgrade(ctx),
-        List(list) => list.downgrade(ctx),
-        BinOp(op) => op.downgrade(ctx),
-        AttrSet(attrs) => attrs.downgrade(ctx),
-        UnaryOp(op) => op.downgrade(ctx),
-        With(with) => with.downgrade(ctx),
-        HasAttr(has) => has.downgrade(ctx),
-
-        _ => unreachable!(),
-    }?;
-    Ok(ctx.new_expr(
-        Thunk {
-            inner: id,
-            // span: ctx.get_span(id),
-            // FIXME: span
-            span: synthetic_span(),
-        }
-        .to_ir(),
-    ))
-}
-
 /// Downgrades the entries of an attribute set.
 /// This handles `inherit` and `attrpath = value;` entries.
 pub fn downgrade_attrs(
@@ -110,7 +59,7 @@ pub fn downgrade_static_attrs(
        }
    }

-    Ok(attrs.stcs)
+    Ok(attrs.stcs.into_iter().map(|(k, (v, _))| (k, v)).collect())
 }

 /// Downgrades an `inherit` statement.
@@ -118,7 +67,7 @@ pub fn downgrade_static_attrs(
 /// `inherit a b;` is translated into `a = a; b = b;` (i.e., bringing variables into scope).
 pub fn downgrade_inherit(
    inherit: ast::Inherit,
-    stcs: &mut HashMap<SymId, ExprId>,
+    stcs: &mut HashMap<SymId, (ExprId, rnix::TextRange)>,
    ctx: &mut impl DowngradeContext,
 ) -> Result<()> {
    // Downgrade the `from` expression if it exists.
@@ -130,21 +79,21 @@ pub fn downgrade_inherit(
    for attr in inherit.attrs() {
        let span = attr.syntax().text_range();
        let ident = match downgrade_attr(attr, ctx)? {
-            Attr::Str(ident) => ident,
+            Attr::Str(ident, _) => ident,
            _ => {
                // `inherit` does not allow dynamic attributes.
                return Err(Error::downgrade_error(
                    "dynamic attributes not allowed in inherit".to_string(),
-                )
-                .with_span(span)
-                .with_source(ctx.get_current_source()));
+                    ctx.get_current_source(),
+                    span,
+                ));
            }
        };
        let expr = if let Some(expr) = from {
            let select_expr = ctx.new_expr(
                Select {
                    expr,
-                    attrpath: vec![Attr::Str(ident)],
+                    attrpath: vec![Attr::Str(ident, span)],
                    default: None,
                    span,
                }
@@ -162,14 +111,18 @@ pub fn downgrade_inherit(
        };
        match stcs.entry(ident) {
            Entry::Occupied(occupied) => {
-                return Err(Error::downgrade_error(format!(
+                return Err(Error::downgrade_error(
+                    format!(
                        "attribute '{}' already defined",
                        format_symbol(ctx.get_sym(*occupied.key()))
-                ))
+                    ),
+                    ctx.get_current_source(),
+                    span,
+                )
                .with_span(span)
                .with_source(ctx.get_current_source()));
            }
-            Entry::Vacant(vacant) => vacant.insert(expr),
+            Entry::Vacant(vacant) => vacant.insert((expr, span)),
        };
    }
    Ok(())
@@ -180,20 +133,24 @@ pub fn downgrade_inherit(
 pub fn downgrade_attr(attr: ast::Attr, ctx: &mut impl DowngradeContext) -> Result<Attr> {
    use ast::Attr::*;
    use ast::InterpolPart::*;
-    let span = attr.syntax().text_range();
    match attr {
-        Ident(ident) => Ok(Attr::Str(ctx.new_sym(ident.to_string()))),
+        Ident(ident) => Ok(Attr::Str(
+            ctx.new_sym(ident.to_string()),
+            ident.syntax().text_range(),
+        )),
        Str(string) => {
            let parts = string.normalized_parts();
+            let span = string.syntax().text_range();
            if parts.is_empty() {
-                Ok(Attr::Str(ctx.new_sym("".to_string())))
+                Ok(Attr::Str(ctx.new_sym("".to_string()), span))
            } else if parts.len() == 1 {
                // If the string has only one part, it's either a literal or a single interpolation.
                match parts.into_iter().next().unwrap() {
-                    Literal(ident) => Ok(Attr::Str(ctx.new_sym(ident))),
-                    Interpolation(interpol) => {
-                        Ok(Attr::Dynamic(interpol.expr().unwrap().downgrade(ctx)?))
-                    }
+                    Literal(ident) => Ok(Attr::Str(ctx.new_sym(ident), span)),
+                    Interpolation(interpol) => Ok(Attr::Dynamic(
+                        interpol.expr().unwrap().downgrade(ctx)?,
+                        span,
+                    )),
                }
            } else {
                // If the string has multiple parts, it's an interpolated string that must be concatenated.
@@ -206,10 +163,14 @@ pub fn downgrade_attr(attr: ast::Attr, ctx: &mut impl DowngradeContext) -> Resul
                    .collect::<Result<Vec<_>>>()?;
                Ok(Attr::Dynamic(
                    ctx.new_expr(ConcatStrings { parts, span }.to_ir()),
+                    span,
                ))
            }
        }
-        Dynamic(dynamic) => Ok(Attr::Dynamic(dynamic.expr().unwrap().downgrade(ctx)?)),
+        Dynamic(dynamic) => Ok(Attr::Dynamic(
+            dynamic.expr().unwrap().downgrade(ctx)?,
+            dynamic.syntax().text_range(),
+        )),
    }
 }

@@ -231,7 +192,8 @@ pub fn downgrade_attrpathvalue(
    ctx: &mut impl DowngradeContext,
 ) -> Result<()> {
    let path = downgrade_attrpath(value.attrpath().unwrap(), ctx)?;
-    let value = maybe_thunk(value.value().unwrap(), ctx)?;
+    let value = value.value().unwrap().downgrade(ctx)?;
+    let value = ctx.maybe_thunk(value);
    attrs.insert(path, value, ctx)
 }

@@ -244,12 +206,14 @@ pub fn downgrade_static_attrpathvalue(
 ) -> Result<()> {
    let attrpath_node = value.attrpath().unwrap();
    let path = downgrade_attrpath(attrpath_node.clone(), ctx)?;
-    if path.iter().any(|attr| matches!(attr, Attr::Dynamic(_))) {
+    if let Some(&Attr::Dynamic(_, span)) =
+        path.iter().find(|attr| matches!(attr, Attr::Dynamic(..)))
+    {
        return Err(Error::downgrade_error(
            "dynamic attributes not allowed in let bindings".to_string(),
-        )
-        .with_span(attrpath_node.syntax().text_range())
-        .with_source(ctx.get_current_source()));
+            ctx.get_current_source(),
+            span,
+        ));
    }
    let value = value.value().unwrap().downgrade(ctx)?;
    attrs.insert(path, value, ctx)
@@ -275,47 +239,53 @@ pub fn downgrade_pattern_bindings<Ctx>(
    pat_entries: impl Iterator<Item = ast::PatEntry>,
    alias: Option<SymId>,
    arg: ExprId,
-    has_ellipsis: bool,
    ctx: &mut Ctx,
    body_fn: impl FnOnce(&mut Ctx, &[SymId]) -> Result<ExprId>,
 ) -> Result<PatternBindings>
 where
    Ctx: DowngradeContext,
 {
-    let mut param_syms = Vec::new();
-    let mut param_defaults = Vec::new();
-    let mut param_spans = Vec::new();
+    struct Param {
+        sym: SymId,
+        sym_span: TextRange,
+        default: Option<ast::Expr>,
+        span: TextRange,
+    }
    let mut seen_params = HashSet::new();
-
-    for entry in pat_entries {
-        let sym = ctx.new_sym(entry.ident().unwrap().to_string());
-        let span = entry.ident().unwrap().syntax().text_range();
+    let (params, mut binding_keys) = pat_entries
+        .into_iter()
+        .map(|entry| {
+            let ident = entry.ident().unwrap();
+            let sym_span = ident.syntax().text_range();
+            let sym = ctx.new_sym(ident.syntax().text().to_string());
+            let default = entry.default();
+            let span = entry.syntax().text_range();

            if !seen_params.insert(sym) {
-            return Err(Error::downgrade_error(format!(
-                "duplicate parameter '{}'",
-                format_symbol(ctx.get_sym(sym))
+                return Err(Error::downgrade_error(
+                    format!("duplicate parameter '{}'", format_symbol(ctx.get_sym(sym))),
+                    ctx.get_current_source(),
+                    span,
+                ));
+            }
+
+            Ok((
+                Param {
+                    sym,
+                    sym_span,
+                    default,
+                    span,
+                },
+                sym,
            ))
-            .with_span(span)
-            .with_source(ctx.get_current_source()));
-        }
+        })
+        .collect::<Result<(Vec<_>, Vec<_>)>>()?;

-        let default_ast = entry.default();
-        param_syms.push(sym);
-        param_defaults.push(default_ast);
-        param_spans.push(span);
-    }
-
-    let mut binding_keys: Vec<SymId> = param_syms.clone();
    if let Some(alias_sym) = alias {
        binding_keys.push(alias_sym);
    }

-    let (required, optional) =
-        param_syms
-            .iter()
-            .zip(param_defaults.iter())
-            .partition_map(|(&sym, default)| {
+    let (required, optional) = params.iter().partition_map(|Param { sym, default, .. }| {
        use itertools::Either::*;
        if default.is_none() {
            Left(sym)
@@ -333,16 +303,18 @@ where
        |ctx, sym_to_slot| {
            let mut bindings = HashMap::new();

-            for ((sym, default_ast), span) in param_syms
-                .iter()
-                .zip(param_defaults.iter())
-                .zip(param_spans.iter())
+            for Param {
+                sym,
+                sym_span,
+                default,
+                span,
+            } in params
            {
-                let slot = *sym_to_slot.get(sym).unwrap();
+                let slot = *sym_to_slot.get(&sym).unwrap();
                ctx.set_current_binding(Some(slot));

-                let default = if let Some(default_expr) = default_ast {
-                    Some(default_expr.clone().downgrade(ctx)?)
+                let default = if let Some(default) = default {
+                    Some(default.clone().downgrade(ctx)?)
                } else {
                    None
                };
@@ -350,13 +322,13 @@ where
                let select_expr = ctx.new_expr(
                    Select {
                        expr: arg,
-                        attrpath: vec![Attr::Str(*sym)],
+                        attrpath: vec![Attr::Str(sym, sym_span)],
                        default,
-                        span: *span,
+                        span,
                    }
                    .to_ir(),
                );
-                bindings.insert(*sym, select_expr);
+                bindings.insert(sym, select_expr);
                ctx.set_current_binding(None);
            }

@@ -433,23 +405,19 @@ where

        for (sym, slot) in binding_keys.iter().copied().zip(slots.iter()) {
            if let Some(&expr) = bindings.get(&sym) {
-                ctx.replace_expr(
+                ctx.replace_ir(
                    *slot,
                    Thunk {
                        inner: expr,
-                        // span: ctx.get_span(expr),
-                        // FIXME: span
-                        span: synthetic_span(),
+                        span: ctx.get_ir(expr).span(),
                    }
                    .to_ir(),
                );
            } else {
-                return Err(Error::downgrade_error(format!(
+                return Err(Error::internal(format!(
                    "binding '{}' not found",
                    format_symbol(ctx.get_sym(sym))
-                ))
-                .with_span(synthetic_span())
-                .with_source(ctx.get_current_source()));
+                )));
            }
        }

@@ -484,12 +452,14 @@ where
                    if let ast::Attr::Ident(ident) = attr {
                        let sym = ctx.new_sym(ident.to_string());
                        if !binding_syms.insert(sym) {
-                            return Err(Error::downgrade_error(format!(
+                            return Err(Error::downgrade_error(
+                                format!(
                                    "attribute '{}' already defined",
                                    format_symbol(ctx.get_sym(sym))
-                            ))
-                            .with_span(ident.syntax().text_range())
-                            .with_source(ctx.get_current_source()));
+                                ),
+                                ctx.get_current_source(),
+                                ident.syntax().text_range(),
+                            ));
                        }
                    }
                }
@@ -504,12 +474,14 @@ where
                    if let Some(ast::Attr::Ident(ident)) = attrs_vec.first() {
                        let sym = ctx.new_sym(ident.to_string());
                        if !binding_syms.insert(sym) {
-                            return Err(Error::downgrade_error(format!(
+                            return Err(Error::downgrade_error(
+                                format!(
                                    "attribute '{}' already defined",
                                    format_symbol(ctx.get_sym(sym))
-                            ))
-                            .with_span(ident.syntax().text_range())
-                            .with_source(ctx.get_current_source()));
+                                ),
+                                ctx.get_current_source(),
+                                ident.syntax().text_range(),
+                            ));
                        }
                    }
                } else if attrs_vec.len() > 1 {
@@ -563,7 +535,11 @@ where
                }
            }

-            Ok(temp_attrs.stcs)
+            Ok(temp_attrs
+                .stcs
+                .into_iter()
+                .map(|(k, (v, _))| (k, v))
+                .collect())
        },
        body_fn,
    )
--- a/nix-js/src/runtime.rs
+++ b/nix-js/src/runtime.rs
@@ -1,13 +1,13 @@
 use std::borrow::Cow;
 use std::marker::PhantomData;
 use std::path::{Component, Path, PathBuf};
-use std::sync::Once;
+use std::sync::{Arc, Once};

 use deno_core::{Extension, ExtensionFileSource, JsRuntime, OpState, RuntimeOptions, v8};
-use deno_error::JsErrorClass;
-use itertools::Itertools as _;
+use rust_embed::Embed;

 use crate::error::{Error, Result, Source};
+use crate::store::Store;
 use crate::value::{AttrSet, List, Symbol, Value};

 type ScopeRef<'p, 's> = v8::PinnedRef<'p, v8::HandleScope<'s>>;
@@ -18,8 +18,24 @@ pub(crate) trait RuntimeContext: 'static {
    fn get_current_dir(&self) -> &Path;
    fn add_source(&mut self, path: Source);
    fn compile_code(&mut self, source: Source) -> Result<String>;
-    fn get_current_source(&self) -> Source;
    fn get_source(&self, id: usize) -> Source;
+    fn get_store(&self) -> &dyn Store;
+}
+
+pub(crate) trait OpStateExt<Ctx: RuntimeContext> {
+    fn get_ctx(&self) -> &Ctx;
+    fn get_ctx_mut(&mut self) -> &mut Ctx;
+}
+
+impl<Ctx: RuntimeContext> OpStateExt<Ctx> for OpState {
+    fn get_ctx(&self) -> &Ctx {
+        self.try_borrow::<&'static mut Ctx>()
+            .expect("RuntimeContext not set")
+    }
+    fn get_ctx_mut(&mut self) -> &mut Ctx {
+        self.try_borrow_mut::<&'static mut Ctx>()
+            .expect("RuntimeContext not set")
+    }
 }

 fn runtime_extension<Ctx: RuntimeContext>() -> Extension {
@@ -28,19 +44,22 @@ fn runtime_extension<Ctx: RuntimeContext>() -> Extension {
    let mut ops = vec![
        op_import::<Ctx>(),
        op_read_file(),
+        op_read_file_type(),
+        op_read_dir(),
        op_path_exists(),
        op_resolve_path(),
        op_sha256_hex(),
-        op_make_store_path(),
+        op_decode_span::<Ctx>(),
+        op_make_store_path::<Ctx>(),
        op_output_path_name(),
-        op_make_fixed_output_path(),
-        op_add_path(),
-        op_store_path(),
-        op_to_file(),
-        op_copy_path_to_store(),
+        op_make_fixed_output_path::<Ctx>(),
+        op_add_path::<Ctx>(),
+        op_store_path::<Ctx>(),
+        op_to_file::<Ctx>(),
+        op_copy_path_to_store::<Ctx>(),
        op_get_env(),
    ];
-    ops.extend(crate::fetcher::register_ops());
+    ops.extend(crate::fetcher::register_ops::<Ctx>());

    Extension {
        name: "nix_runtime",
@@ -79,6 +98,10 @@ mod private {
 }
 pub(crate) use private::NixError;

+#[derive(Embed)]
+#[folder = "src/runtime/corepkgs"]
+pub(crate) struct CorePkgs;
+
 #[deno_core::op2]
 #[string]
 fn op_import<Ctx: RuntimeContext>(
@@ -86,7 +109,25 @@ fn op_import<Ctx: RuntimeContext>(
    #[string] path: String,
 ) -> std::result::Result<String, NixError> {
    let _span = tracing::info_span!("op_import", path = %path).entered();
-    let ctx = state.borrow_mut::<Ctx>();
+    let ctx: &mut Ctx = state.get_ctx_mut();
+
+    // FIXME: special path type
+    if path.starts_with("<nix/") && path.ends_with(">") {
+        let corepkg_name = &path[5..path.len() - 1];
+        if let Some(file) = CorePkgs::get(corepkg_name) {
+            tracing::info!("Importing corepkg: {}", corepkg_name);
+            let source = Source {
+                ty: crate::error::SourceType::Eval(Arc::new(ctx.get_current_dir().to_path_buf())),
+                src: str::from_utf8(&file.data)
+                    .expect("corrupted corepkgs file")
+                    .into(),
+            };
+            ctx.add_source(source.clone());
+            return Ok(ctx.compile_code(source).map_err(|err| err.to_string())?);
+        } else {
+            return Err(format!("Corepkg not found: {}", corepkg_name).into());
+        }
+    }

    let current_dir = ctx.get_current_dir();
    let mut absolute_path = current_dir
@@ -123,6 +164,71 @@ fn op_path_exists(#[string] path: String) -> bool {
    std::path::Path::new(&path).exists()
 }

+#[deno_core::op2]
+#[string]
+fn op_read_file_type(#[string] path: String) -> std::result::Result<String, NixError> {
+    let path = Path::new(&path);
+    let metadata = std::fs::symlink_metadata(path)
+        .map_err(|e| format!("Failed to read file type for {}: {}", path.display(), e))?;
+
+    let file_type = metadata.file_type();
+    let type_str = if file_type.is_dir() {
+        "directory"
+    } else if file_type.is_symlink() {
+        "symlink"
+    } else if file_type.is_file() {
+        "regular"
+    } else {
+        "unknown"
+    };
+
+    Ok(type_str.to_string())
+}
+
+#[deno_core::op2]
+#[serde]
+fn op_read_dir(
+    #[string] path: String,
+) -> std::result::Result<std::collections::HashMap<String, String>, NixError> {
+    let path = Path::new(&path);
+
+    if !path.is_dir() {
+        return Err(format!("{} is not a directory", path.display()).into());
+    }
+
+    let entries = std::fs::read_dir(path)
+        .map_err(|e| format!("Failed to read directory {}: {}", path.display(), e))?;
+
+    let mut result = std::collections::HashMap::new();
+
+    for entry in entries {
+        let entry = entry.map_err(|e| format!("Failed to read directory entry: {}", e))?;
+        let file_name = entry.file_name().to_string_lossy().to_string();
+
+        let file_type = entry.file_type().map_err(|e| {
+            format!(
+                "Failed to read file type for {}: {}",
+                entry.path().display(),
+                e
+            )
+        })?;
+
+        let type_str = if file_type.is_dir() {
+            "directory"
+        } else if file_type.is_symlink() {
+            "symlink"
+        } else if file_type.is_file() {
+            "regular"
+        } else {
+            "unknown"
+        };
+
+        result.insert(file_name, type_str.to_string());
+    }
+
+    Ok(result)
+}
+
 #[deno_core::op2]
 #[string]
 fn op_resolve_path(
@@ -168,19 +274,67 @@ fn op_sha256_hex(#[string] data: String) -> String {
    crate::nix_hash::sha256_hex(&data)
 }

+#[deno_core::op2]
+#[serde]
+fn op_decode_span<Ctx: RuntimeContext>(
+    state: &mut OpState,
+    #[string] span_str: String,
+) -> std::result::Result<serde_json::Value, NixError> {
+    let parts: Vec<&str> = span_str.split(':').collect();
+    if parts.len() != 3 {
+        return Ok(serde_json::json!({
+            "file": serde_json::Value::Null,
+            "line": serde_json::Value::Null,
+            "column": serde_json::Value::Null
+        }));
+    }
+
+    let source_id: usize = parts[0].parse().map_err(|_| "Invalid source ID")?;
+    let start: u32 = parts[1].parse().map_err(|_| "Invalid start offset")?;
+
+    let ctx: &Ctx = state.get_ctx();
+    let source = ctx.get_source(source_id);
+    let content = &source.src;
+
+    let (line, column) = byte_offset_to_line_col(content, start as usize);
+
+    Ok(serde_json::json!({
+        "file": source.get_name(),
+        "line": line,
+        "column": column
+    }))
+}
+
+fn byte_offset_to_line_col(content: &str, offset: usize) -> (u32, u32) {
+    let mut line = 1u32;
+    let mut col = 1u32;
+
+    for (idx, ch) in content.char_indices() {
+        if idx >= offset {
+            break;
+        }
+        if ch == '\n' {
+            line += 1;
+            col = 1;
+        } else {
+            col += 1;
+        }
+    }
+
+    (line, col)
+}
+
 #[deno_core::op2]
 #[string]
-fn op_make_store_path(
+fn op_make_store_path<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] ty: String,
    #[string] hash_hex: String,
    #[string] name: String,
 ) -> String {
-    use crate::store::StoreBackend;
-    use std::sync::Arc;
-
-    let store = state.borrow::<Arc<StoreBackend>>();
-    let store_dir = store.as_store().get_store_dir();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();
+    let store_dir = store.get_store_dir();
    crate::nix_hash::make_store_path(store_dir, &ty, &hash_hex, &name)
 }

@@ -192,19 +346,18 @@ fn op_output_path_name(#[string] drv_name: String, #[string] output_name: String

 #[deno_core::op2]
 #[string]
-fn op_make_fixed_output_path(
+fn op_make_fixed_output_path<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] hash_algo: String,
    #[string] hash: String,
    #[string] hash_mode: String,
    #[string] name: String,
 ) -> String {
-    use crate::store::StoreBackend;
    use sha2::{Digest, Sha256};
-    use std::sync::Arc;

-    let store = state.borrow::<Arc<StoreBackend>>();
-    let store_dir = store.as_store().get_store_dir();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();
+    let store_dir = store.get_store_dir();

    if hash_algo == "sha256" && hash_mode == "recursive" {
        crate::nix_hash::make_store_path(store_dir, "source", &hash, &name)
@@ -221,18 +374,16 @@ fn op_make_fixed_output_path(

 #[deno_core::op2]
 #[string]
-fn op_add_path(
+fn op_add_path<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] path: String,
    #[string] name: Option<String>,
    recursive: bool,
    #[string] sha256: Option<String>,
 ) -> std::result::Result<String, NixError> {
-    use crate::store::StoreBackend;
    use sha2::{Digest, Sha256};
    use std::fs;
    use std::path::Path;
-    use std::sync::Arc;

    let path_obj = Path::new(&path);

@@ -273,10 +424,10 @@ fn op_add_path(
        )));
    }

-    let store = state.borrow::<Arc<StoreBackend>>();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();

    let store_path = store
-        .as_store()
        .add_to_store_from_path(&computed_name, path_obj, vec![])
        .map_err(|e| NixError::from(format!("failed to add path to store: {}", e)))?;

@@ -320,20 +471,19 @@ fn compute_nar_hash(path: &std::path::Path) -> std::result::Result<String, NixEr

 #[deno_core::op2]
 #[string]
-fn op_store_path(
+fn op_store_path<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] path: String,
 ) -> std::result::Result<String, NixError> {
-    use crate::store::{StoreBackend, validate_store_path};
-    use std::sync::Arc;
+    use crate::store::validate_store_path;

-    let store = state.borrow::<Arc<StoreBackend>>();
-    let store_dir = store.as_store().get_store_dir();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();
+    let store_dir = store.get_store_dir();

    validate_store_path(store_dir, &path).map_err(|e| NixError::from(e.to_string()))?;

    store
-        .as_store()
        .ensure_path(&path)
        .map_err(|e| NixError::from(e.to_string()))?;

@@ -342,18 +492,15 @@ fn op_store_path(

 #[deno_core::op2]
 #[string]
-fn op_to_file(
+fn op_to_file<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] name: String,
    #[string] contents: String,
    #[serde] references: Vec<String>,
 ) -> std::result::Result<String, NixError> {
-    use crate::store::StoreBackend;
-    use std::sync::Arc;
-
-    let store = state.borrow::<Arc<StoreBackend>>();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();
    let store_path = store
-        .as_store()
        .add_text_to_store(&name, &contents, references)
        .map_err(|e| NixError::from(format!("builtins.toFile failed: {}", e)))?;

@@ -362,13 +509,11 @@ fn op_to_file(

 #[deno_core::op2]
 #[string]
-fn op_copy_path_to_store(
+fn op_copy_path_to_store<Ctx: RuntimeContext>(
    state: &mut OpState,
    #[string] path: String,
 ) -> std::result::Result<String, NixError> {
-    use crate::store::StoreBackend;
    use std::path::Path;
-    use std::sync::Arc;

    let path_obj = Path::new(&path);

@@ -382,9 +527,9 @@ fn op_copy_path_to_store(
        .unwrap_or("source")
        .to_string();

-    let store = state.borrow::<Arc<StoreBackend>>();
+    let ctx: &Ctx = state.get_ctx();
+    let store = ctx.get_store();
    let store_path = store
-        .as_store()
        .add_to_store_from_path(&name, path_obj, vec![])
        .map_err(|e| NixError::from(format!("failed to copy path to store: {}", e)))?;

@@ -437,51 +582,20 @@ impl<Ctx: RuntimeContext> Runtime<Ctx> {
        })
    }

-    pub(crate) fn op_state(&mut self) -> std::rc::Rc<std::cell::RefCell<OpState>> {
-        self.js_runtime.op_state()
-    }
-
-    pub(crate) fn eval(&mut self, script: String, ctx: Ctx) -> Result<Value> {
+    pub(crate) fn eval(&mut self, script: String, ctx: &mut Ctx) -> Result<Value> {
+        let ctx: &'static mut Ctx = unsafe { &mut *(ctx as *mut Ctx) };
        self.js_runtime.op_state().borrow_mut().put(ctx);

        let global_value = self
            .js_runtime
            .execute_script("<eval>", script)
-            .map_err(|e| {
+            .map_err(|error| {
                // Get current source from Context
                let op_state = self.js_runtime.op_state();
                let op_state_borrow = op_state.borrow();
-                let ctx = op_state_borrow.borrow::<Ctx>();
+                let ctx: &Ctx = op_state_borrow.get_ctx();

-                let msg = e.get_message().to_string();
-                let mut span = None;
-                let mut source = None;
-
-                // Parse Nix stack trace frames
-                if let Some(stack) = &e.stack {
-                    let frames = crate::error::parse_nix_stack(stack, ctx);
-
-                    if let Some(last_frame) = frames.last() {
-                        span = Some(last_frame.span);
-                        source = Some(last_frame.source.clone())
-                    }
-                }
-
-                let js_backtrace = e.stack.map(|stack| {
-                    stack
-                        .lines()
-                        .filter(|line| !line.starts_with("NIX_STACK_FRAME:"))
-                        .join("\n")
-                });
-                let mut error = Error::eval_error(msg.clone(), js_backtrace);
-                if let Some(span) = span {
-                    error = error.with_span(span);
-                }
-                if let Some(source) = source {
-                    error = error.with_source(source);
-                }
-
-                error
+                crate::error::parse_js_error(error, ctx)
            })?;

        // Retrieve scope from JsRuntime
--- a/nix-js/src/runtime/corepkgs/fetchurl.nix
+++ b/nix-js/src/runtime/corepkgs/fetchurl.nix
@@ -0,0 +1,76 @@
+{
+  system ? "", # obsolete
+  url,
+  hash ? "", # an SRI hash
+
+  # Legacy hash specification
+  md5 ? "",
+  sha1 ? "",
+  sha256 ? "",
+  sha512 ? "",
+  outputHash ?
+    if hash != "" then
+      hash
+    else if sha512 != "" then
+      sha512
+    else if sha1 != "" then
+      sha1
+    else if md5 != "" then
+      md5
+    else
+      sha256,
+  outputHashAlgo ?
+    if hash != "" then
+      ""
+    else if sha512 != "" then
+      "sha512"
+    else if sha1 != "" then
+      "sha1"
+    else if md5 != "" then
+      "md5"
+    else
+      "sha256",
+
+  executable ? false,
+  unpack ? false,
+  name ? baseNameOf (toString url),
+  # still translates to __impure to trigger derivationStrict error checks.
+  impure ? false,
+}:
+
+derivation (
+  {
+    builder = "builtin:fetchurl";
+
+    # New-style output content requirements.
+    outputHashMode = if unpack || executable then "recursive" else "flat";
+
+    inherit
+      name
+      url
+      executable
+      unpack
+      ;
+
+    system = "builtin";
+
+    # No need to double the amount of network traffic
+    preferLocalBuild = true;
+
+    impureEnvVars = [
+      # We borrow these environment variables from the caller to allow
+      # easy proxy configuration.  This is impure, but a fixed-output
+      # derivation like fetchurl is allowed to do so since its result is
+      # by definition pure.
+      "http_proxy"
+      "https_proxy"
+      "ftp_proxy"
+      "all_proxy"
+      "no_proxy"
+    ];
+
+    # To make "nix-prefetch-url" work.
+    urls = [ url ];
+  }
+  // (if impure then { __impure = true; } else { inherit outputHashAlgo outputHash; })
+)
--- a/nix-js/src/store.rs
+++ b/nix-js/src/store.rs
@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 mod config;
 mod error;
 mod validation;
--- a/nix-js/tests/builtins.rs
+++ b/nix-js/tests/builtins.rs
@@ -315,3 +315,13 @@ fn builtins_function_args() {
        ])))
    );
 }
+
+#[test]
+fn builtins_parse_drv_name() {
+    let result = eval(r#"builtins.parseDrvName "nix-js-0.1.0pre""#).unwrap_attr_set();
+    assert_eq!(result.get("name"), Some(&Value::String("nix-js".into())));
+    assert_eq!(
+        result.get("version"),
+        Some(&Value::String("0.1.0pre".into()))
+    );
+}
--- a/nix-js/tests/derivation.rs
+++ b/nix-js/tests/derivation.rs
@@ -143,9 +143,10 @@ fn derivation_strict() {

    match result {
        Value::AttrSet(attrs) => {
-            assert_eq!(attrs.get("type"), Some(&Value::String("derivation".into())));
            assert!(attrs.contains_key("drvPath"));
-            assert!(attrs.contains_key("outPath"));
+            assert!(attrs.contains_key("out"));
+            assert!(!attrs.contains_key("type"));
+            assert!(!attrs.contains_key("outPath"));
        }
        _ => panic!("Expected AttrSet"),
    }
@@ -189,7 +190,7 @@ fn derivation_escaping_in_aterm() {

 #[test]
 fn multi_output_two_outputs() {
-    let result = eval(
+    let drv = eval(
        r#"derivation {
            name = "multi";
            builder = "/bin/sh";
@@ -198,39 +199,23 @@ fn multi_output_two_outputs() {
        }"#,
    );

-    match result {
+    match drv {
        Value::AttrSet(attrs) => {
+            assert!(attrs.contains_key("drvPath"));
            assert!(attrs.contains_key("out"));
            assert!(attrs.contains_key("dev"));
            assert!(attrs.contains_key("outPath"));
-            assert!(attrs.contains_key("drvPath"));

-            // Verify exact paths match CppNix
            if let Some(Value::String(drv_path)) = attrs.get("drvPath") {
                assert_eq!(
                    drv_path,
                    "/nix/store/vmyjryfipkn9ss3ya23hk8p3m58l6dsl-multi.drv"
                );
            } else {
-                panic!("drvPath should be a string");
-            }
-
-            if let Some(Value::String(out_path)) = attrs.get("out") {
-                assert_eq!(
-                    out_path,
-                    "/nix/store/a3d95yg9d215c54n0ybr4npmpnj29229-multi"
+                panic!(
+                    "drvPath should be a string, got: {:?}",
+                    attrs.get("drvPath")
                );
-            } else {
-                panic!("out should be a string");
-            }
-
-            if let Some(Value::String(dev_path)) = attrs.get("dev") {
-                assert_eq!(
-                    dev_path,
-                    "/nix/store/hq3b99lz71gwfq6x8lqwg14hf929q0d2-multi-dev"
-                );
-            } else {
-                panic!("dev should be a string");
            }

            if let Some(Value::String(out_path)) = attrs.get("outPath") {
@@ -238,7 +223,8 @@ fn multi_output_two_outputs() {
                    out_path,
                    "/nix/store/a3d95yg9d215c54n0ybr4npmpnj29229-multi"
                );
-                assert_eq!(attrs.get("out"), Some(&Value::String(out_path.clone())));
+            } else {
+                panic!("outPath should be a string");
            }
        }
        _ => panic!("Expected AttrSet"),
--- a/nix-js/tests/findfile.rs
+++ b/nix-js/tests/findfile.rs
@@ -0,0 +1,38 @@
+mod utils;
+
+use utils::eval;
+
+#[test]
+fn test_find_file_corepkg_fetchurl() {
+    let result = eval(
+        r#"
+        let
+          searchPath = [];
+          lookupPath = "nix/fetchurl.nix";
+        in
+          builtins.findFile searchPath lookupPath
+        "#,
+    );
+
+    assert!(result.to_string().contains("fetchurl.nix"));
+}
+
+#[test]
+fn test_lookup_path_syntax() {
+    let result = eval(r#"<nix/fetchurl.nix>"#);
+    assert!(result.to_string().contains("fetchurl.nix"));
+}
+
+#[test]
+fn test_import_corepkg() {
+    let result = eval(
+        r#"
+        let
+          fetchurl = import <nix/fetchurl.nix>;
+        in
+          builtins.typeOf fetchurl
+        "#,
+    );
+
+    assert_eq!(result.to_string(), "\"lambda\"");
+}
--- a/nix-js/tests/io_operations.rs
+++ b/nix-js/tests/io_operations.rs
@@ -260,3 +260,111 @@ fn path_deterministic() {
    // Same inputs should produce same store path
    assert_eq!(result1, result2);
 }
+
+#[test]
+fn read_file_type_regular_file() {
+    let temp_dir = tempfile::tempdir().unwrap();
+    let test_file = temp_dir.path().join("test.txt");
+    std::fs::write(&test_file, "Test content").unwrap();
+
+    let expr = format!(r#"builtins.readFileType {}"#, test_file.display());
+    assert_eq!(eval(&expr), Value::String("regular".to_string()));
+}
+
+#[test]
+fn read_file_type_directory() {
+    let temp_dir = tempfile::tempdir().unwrap();
+    let test_dir = temp_dir.path().join("testdir");
+    std::fs::create_dir(&test_dir).unwrap();
+
+    let expr = format!(r#"builtins.readFileType {}"#, test_dir.display());
+    assert_eq!(eval(&expr), Value::String("directory".to_string()));
+}
+
+#[test]
+fn read_file_type_symlink() {
+    let temp_dir = tempfile::tempdir().unwrap();
+    let target = temp_dir.path().join("target.txt");
+    let symlink = temp_dir.path().join("link.txt");
+
+    std::fs::write(&target, "Target content").unwrap();
+
+    #[cfg(unix)]
+    std::os::unix::fs::symlink(&target, &symlink).unwrap();
+
+    #[cfg(unix)]
+    {
+        let expr = format!(r#"builtins.readFileType {}"#, symlink.display());
+        assert_eq!(eval(&expr), Value::String("symlink".to_string()));
+    }
+}
+
+#[test]
+fn read_dir_basic() {
+    let temp_dir = tempfile::tempdir().unwrap();
+    let test_dir = temp_dir.path().join("readdir_test");
+    std::fs::create_dir(&test_dir).unwrap();
+
+    std::fs::write(test_dir.join("file1.txt"), "Content 1").unwrap();
+    std::fs::write(test_dir.join("file2.txt"), "Content 2").unwrap();
+    std::fs::create_dir(test_dir.join("subdir")).unwrap();
+
+    let expr = format!(r#"builtins.readDir {}"#, test_dir.display());
+    let result = eval(&expr);
+
+    if let Value::AttrSet(attrs) = result {
+        assert_eq!(
+            attrs.get("file1.txt"),
+            Some(&Value::String("regular".to_string()))
+        );
+        assert_eq!(
+            attrs.get("file2.txt"),
+            Some(&Value::String("regular".to_string()))
+        );
+        assert_eq!(
+            attrs.get("subdir"),
+            Some(&Value::String("directory".to_string()))
+        );
+        assert_eq!(attrs.len(), 3);
+    } else {
+        panic!("Expected AttrSet, got {:?}", result);
+    }
+}
+
+#[test]
+fn read_dir_empty() {
+    let temp_dir = tempfile::tempdir().unwrap();
+    let test_dir = temp_dir.path().join("empty_dir");
+    std::fs::create_dir(&test_dir).unwrap();
+
+    let expr = format!(r#"builtins.readDir {}"#, test_dir.display());
+    let result = eval(&expr);
+
+    if let Value::AttrSet(attrs) = result {
+        assert_eq!(attrs.len(), 0);
+    } else {
+        panic!("Expected AttrSet, got {:?}", result);
+    }
+}
+
+#[test]
+fn read_dir_nonexistent_fails() {
+    let expr = r#"builtins.readDir "/nonexistent/directory""#;
+    let result = eval_result(expr);
+
+    assert!(result.is_err());
+}
+
+#[test]
+fn read_dir_on_file_fails() {
+    let temp_dir = tempfile::tempdir().unwrap();
+    let test_file = temp_dir.path().join("test.txt");
+    std::fs::write(&test_file, "Test content").unwrap();
+
+    let expr = format!(r#"builtins.readDir {}"#, test_file.display());
+    let result = eval_result(&expr);
+
+    assert!(result.is_err());
+    let err_msg = result.unwrap_err().to_string();
+    assert!(err_msg.contains("not a directory"));
+}
Author	SHA1	Message	Date
imxyy_soope_	3186cfe6e4	feat(error): stack trace	2026-01-25 03:06:13 +08:00
imxyy_soope_	4d68fb26d9	fix: derivation & derivationStrict	2026-01-25 03:06:13 +08:00
imxyy_soope_	51f7f4079b	feat: builtins.parseDrvName	2026-01-25 03:06:13 +08:00
imxyy_soope_	7136f57c12	feat: builtins.unsafeGetAttrPos & __curPos	2026-01-25 03:06:13 +08:00
imxyy_soope_	05b66070a3	feat: builtins.readType & builtins.readDir	2026-01-25 03:06:13 +08:00
imxyy_soope_	13a7d761f4	feat: lookup path (builtins.findFile)	2026-01-25 03:06:13 +08:00
imxyy_soope_	3d315cd050	feat: debug thunk location	2026-01-25 03:06:13 +08:00
imxyy_soope_	62ec37f3ad	feat: mkAttrs	2026-01-25 03:06:13 +08:00
imxyy_soope_	a6aded7bea	fix: return defaultVal when lhs is not attrset in selectWithDefault	2026-01-25 03:06:13 +08:00
imxyy_soope_	296c0398a4	fix(builtins.zipAttrsWith): laziness	2026-01-25 03:06:13 +08:00
imxyy_soope_	10430e2006	refactor: RuntimeContext	2026-01-25 03:06:13 +08:00
imxyy_soope_	f46ee9d48f	chore: tidy	2026-01-24 11:20:12 +08:00
imxyy_soope_	e58ebbe408	fix: maybe_thunk	2026-01-24 02:20:33 +08:00
imxyy_soope_	2f5f84c6c1	fix: removeAttrs	2026-01-24 01:58:08 +08:00