feat: builtins.placeholder

nix-js/runtime-ts/src/builtins/misc.ts

@@ -262,8 +262,9 @@ export const parseFlakeRef = (s: NixValue): never => {
   throw new Error("Not implemented: parseFlakeRef");
 };
 
-export const placeholder = (output: NixValue): never => {
-  throw new Error("Not implemented: placeholder");
+export const placeholder = (output: NixValue): NixValue => {
+  const outputStr = forceStringNoCtx(output);
+  return Deno.core.ops.op_make_placeholder(outputStr);
 };
 
 export const replaceStrings =

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_make_placeholder(output: 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;

nix-js/src/runtime.rs

@@ -49,6 +49,7 @@ fn runtime_extension<Ctx: RuntimeContext>() -> Extension {
         op_path_exists(),
         op_resolve_path(),
         op_sha256_hex(),
+        op_make_placeholder(),
         op_decode_span::<Ctx>(),
         op_make_store_path::<Ctx>(),
         op_output_path_name(),
@@ -132,12 +133,11 @@ fn op_import<Ctx: RuntimeContext>(
     }
 
     let current_dir = ctx.get_current_dir();
-    let mut absolute_path = current_dir
-        .join(&path);
-        // Do NOT resolve symlinks (eval-okay-symlink-resolution)
-        // TODO: is this correct?
-        // .canonicalize()
-        // .map_err(|e| format!("Failed to resolve path {}: {}", path, e))?;
+    let mut absolute_path = current_dir.join(&path);
+    // Do NOT resolve symlinks (eval-okay-symlink-resolution)
+    // TODO: is this correct?
+    // .canonicalize()
+    // .map_err(|e| format!("Failed to resolve path {}: {}", path, e))?;
     if absolute_path.is_dir() {
         absolute_path.push("default.nix")
     }
@@ -284,6 +284,18 @@ fn op_sha256_hex(#[string] data: String) -> String {
     crate::nix_hash::sha256_hex(&data)
 }
 
+#[deno_core::op2]
+#[string]
+fn op_make_placeholder(#[string] output: String) -> String {
+    use sha2::{Digest, Sha256};
+    let input = format!("nix-output:{}", output);
+    let mut hasher = Sha256::new();
+    hasher.update(input.as_bytes());
+    let hash: [u8; 32] = hasher.finalize().into();
+    let encoded = crate::nix_hash::nix_base32_encode(&hash);
+    format!("/{}", encoded)
+}
+
 #[deno_core::op2]
 #[serde]
 fn op_decode_span<Ctx: RuntimeContext>(