diff --git a/nix-js/runtime-ts/src/builtins/attrs.ts b/nix-js/runtime-ts/src/builtins/attrs.ts
index 01d7c09..93755da 100644
--- a/nix-js/runtime-ts/src/builtins/attrs.ts
+++ b/nix-js/runtime-ts/src/builtins/attrs.ts
@@ -140,3 +140,22 @@ export const zipAttrsWith =
 
     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);
+  };
diff --git a/nix-js/runtime-ts/src/builtins/index.ts b/nix-js/runtime-ts/src/builtins/index.ts
index abe334c..2dd3c35 100644
--- a/nix-js/runtime-ts/src/builtins/index.ts
+++ b/nix-js/runtime-ts/src/builtins/index.ts
@@ -173,6 +173,7 @@ export const builtins: any = {
   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),
@@ -232,7 +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),
diff --git a/nix-js/runtime-ts/src/builtins/misc.ts b/nix-js/runtime-ts/src/builtins/misc.ts
index d8ea458..d4f7f09 100644
--- a/nix-js/runtime-ts/src/builtins/misc.ts
+++ b/nix-js/runtime-ts/src/builtins/misc.ts
@@ -5,7 +5,7 @@
 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 } from "../operators";
 import { isBool, isFloat, isInt, isList, isString, typeOf } from "./type-check";
@@ -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 =
diff --git a/nix-js/runtime-ts/src/helpers.ts b/nix-js/runtime-ts/src/helpers.ts
index ab4549b..647095a 100644
--- a/nix-js/runtime-ts/src/helpers.ts
+++ b/nix-js/runtime-ts/src/helpers.ts
@@ -388,3 +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);
+};
diff --git a/nix-js/runtime-ts/src/index.ts b/nix-js/runtime-ts/src/index.ts
index e515e54..88cd884 100644
--- 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, mkAttrs, mkFunction } from "./types";
+import { IS_PATH, mkAttrs, mkFunction, mkAttrsWithPos, ATTR_POSITIONS } from "./types";
 import { forceBool } from "./type-assert";
 
 export type NixRuntime = typeof Nix;
@@ -53,7 +54,10 @@ export const Nix = {
   concatStringsWithContext,
   StringCoercionMode,
   mkAttrs,
+  mkAttrsWithPos,
   mkFunction,
+  mkPos,
+  ATTR_POSITIONS,
 
   pushContext,
   popContext,
diff --git a/nix-js/runtime-ts/src/types.ts b/nix-js/runtime-ts/src/types.ts
index 86b6439..0d42a79 100644
--- a/nix-js/runtime-ts/src/types.ts
+++ b/nix-js/runtime-ts/src/types.ts
@@ -87,6 +87,39 @@ export const mkAttrs = (attrs: NixAttrs, keys: NixValue[], values: NixValue[]):
   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
  * Thunks delay evaluation until forced
diff --git a/nix-js/runtime-ts/src/types/global.d.ts b/nix-js/runtime-ts/src/types/global.d.ts
index 8fe747f..9d887bc 100644
--- a/nix-js/runtime-ts/src/types/global.d.ts
+++ b/nix-js/runtime-ts/src/types/global.d.ts
@@ -42,6 +42,7 @@ declare global {
         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(
diff --git a/nix-js/src/codegen.rs b/nix-js/src/codegen.rs
index fe79f27..bdbfe38 100644
--- a/nix-js/src/codegen.rs
+++ b/nix-js/src/codegen.rs
@@ -171,6 +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)
+            }
         }
     }
 }
@@ -346,9 +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);
 
@@ -362,12 +367,15 @@ 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));
         }
 
         if !self.dyns.is_empty() {
-            let (keys, vals) = self.dyns.iter().map(|&(key, val)| {
-                let key = ctx.get_ir(key).compile(ctx);
-                let val_expr = ctx.get_ir(val);
+            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 {
@@ -379,9 +387,19 @@ impl<Ctx: CodegenContext> Compile<Ctx> for AttrSet {
                 } else {
                     val
                 };
-                (key, val)
-            }).collect::<(Vec<_>, Vec<_>)>();
-            format!("Nix.mkAttrs({{{}}},[{}],[{}])", attrs.join(","), keys.join(","), vals.join(","))
+                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(","))
         }
diff --git a/nix-js/src/ir.rs b/nix-js/src/ir.rs
index 73d23d6..064a3a1 100644
--- a/nix-js/src/ir.rs
+++ b/nix-js/src/ir.rs
@@ -59,7 +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> },
@@ -78,6 +78,7 @@ ir! {
     Thunk(ExprId),
     Builtins,
     Builtin(SymId),
+    CurPos,
 }
 
 impl Ir {
@@ -106,6 +107,7 @@ impl Ir {
             Ir::Thunk(t) => t.span,
             Ir::Builtins(b) => b.span,
             Ir::Builtin(b) => b.span,
+            Ir::CurPos(c) => c.span,
         }
     }
 }
@@ -123,7 +125,7 @@ impl AttrSet {
             match attr {
                 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_ir(id);
                         let result = ir
@@ -151,8 +153,8 @@ impl AttrSet {
                             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(())
                 }
@@ -166,7 +168,7 @@ impl AttrSet {
                         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(())
                 }
             }
@@ -174,7 +176,7 @@ impl AttrSet {
             // This is the final attribute in the path, so insert the value here.
             match name {
                 Attr::Str(ident, span) => {
-                    if self.stcs.insert(ident, value).is_some() {
+                    if self.stcs.insert(ident, (value, span)).is_some() {
                         return Err(Error::downgrade_error(
                             format!(
                                 "attribute '{}' already defined",
@@ -185,8 +187,8 @@ impl AttrSet {
                         ));
                     }
                 }
-                Attr::Dynamic(dynamic, _) => {
-                    self.dyns.push((dynamic, value));
+                Attr::Dynamic(dynamic, span) => {
+                    self.dyns.push((dynamic, value, span));
                 }
             }
             Ok(())
diff --git a/nix-js/src/ir/downgrade.rs b/nix-js/src/ir/downgrade.rs
index 35eb135..686f5de 100644
--- a/nix-js/src/ir/downgrade.rs
+++ b/nix-js/src/ir/downgrade.rs
@@ -174,9 +174,15 @@ 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)
     }
 }
 
@@ -203,7 +209,7 @@ 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()))
@@ -325,7 +331,7 @@ 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()))
@@ -334,7 +340,6 @@ impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::LegacyLet {
         let body_sym = ctx.new_sym("body".to_string());
         let select = Select {
             expr: attrset_expr,
-            // FIXME: span
             attrpath: vec![Attr::Str(body_sym, synthetic_span())],
             default: None,
             span,
diff --git a/nix-js/src/ir/utils.rs b/nix-js/src/ir/utils.rs
index 6ed4749..b6ebaf3 100644
--- a/nix-js/src/ir/utils.rs
+++ b/nix-js/src/ir/utils.rs
@@ -59,7 +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.
@@ -67,7 +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.
@@ -122,7 +122,7 @@ pub fn downgrade_inherit(
                 .with_span(span)
                 .with_source(ctx.get_current_source()));
             }
-            Entry::Vacant(vacant) => vacant.insert(expr),
+            Entry::Vacant(vacant) => vacant.insert((expr, span)),
         };
     }
     Ok(())
@@ -534,7 +534,7 @@ where
                 }
             }
 
-            Ok(temp_attrs.stcs)
+            Ok(temp_attrs.stcs.into_iter().map(|(k, (v, _))| (k, v)).collect())
         },
         body_fn,
     )
diff --git a/nix-js/src/runtime.rs b/nix-js/src/runtime.rs
index 5711e33..d39d95d 100644
--- a/nix-js/src/runtime.rs
+++ b/nix-js/src/runtime.rs
@@ -51,6 +51,7 @@ fn runtime_extension<Ctx: RuntimeContext>() -> Extension {
         op_path_exists(),
         op_resolve_path(),
         op_sha256_hex(),
+        op_decode_span::<Ctx>(),
         op_make_store_path::<Ctx>(),
         op_output_path_name(),
         op_make_fixed_output_path::<Ctx>(),
@@ -268,6 +269,56 @@ 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<Ctx: RuntimeContext>(