feat(stdlib/bun): bun_run_capture — captured child-process run

lib/codegen_deno.ml

@@ -1339,6 +1339,18 @@ let () =
       Printf.sprintf
         "(__as_childProcess().spawnSync(%s, %s, { stdio: \"inherit\" }).status ?? 1)"
         (arg 0 a) (arg 1 a));
+  (* Captured run: stdin closed, stdout/stderr piped as UTF-8. [cwd] is an
+     AffineScript Option ({ tag, value }). A host spawn error (ENOENT,
+     ENOBUFS) has no status, so it maps to 1 with its message on stderr. *)
+  b "bun_run_capture"
+    (fun a ->
+      Printf.sprintf
+        "((__r) => ({ status: __r.status ?? 1, stdout: __r.stdout ?? \"\", \
+         stderr: (__r.stderr ?? \"\") + (__r.error ? String(__r.error.message) : \"\") }))\
+         (__as_childProcess().spawnSync(%s, %s, { encoding: \"utf8\", \
+         stdio: [\"ignore\", \"pipe\", \"pipe\"], \
+         cwd: ((__c) => __c.tag === \"Some\" ? __c.value : undefined)(%s) }))"
+        (arg 0 a) (arg 1 a) (arg 2 a));
   b "bun_stdin_text"
     (fun _ -> "__as_fs().readFileSync(0, \"utf8\")");
   b "bun_stdout_write"

stdlib/Bun.affine

@@ -16,6 +16,23 @@ pub extern fn bun_env_get(name: String) -> Option<String>;
 /// its exit status (or 1 when the host supplies no status).
 pub extern fn bun_run(command: String, arguments: [String]) -> Int;
 
+/// The captured outcome of a child process: its exit status (1 when the host
+/// supplies none, e.g. on a signal or a spawn failure) and its standard output
+/// and standard error decoded as UTF-8.
+pub type RunResult = {
+  status: Int,
+  stdout: String,
+  stderr: String
+}
+
+/// Run a child process synchronously and capture its standard output and
+/// standard error instead of inheriting them. Standard input is closed.
+/// `cwd` sets the child's working directory; `None` keeps the caller's. A
+/// spawn failure (missing program, output over the host buffer limit) yields
+/// status 1 with the host's error message appended to `stderr`.
+pub extern fn bun_run_capture(command: String, arguments: [String],
+                              cwd: Option<String>) -> RunResult;
+
 /// Read standard input to EOF as UTF-8.
 pub extern fn bun_stdin_text() -> String;
 

tests/codegen-bun/host_profile.affine

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 // Bun-ESM host-profile acceptance fixture (issue #734).
 
-use Bun::{ bun_env_get, bun_run, bun_stdin_text, bun_stdout_write, bun_stderr_write, bun_exit };
+use Bun::{ RunResult, bun_env_get, bun_run, bun_run_capture, bun_stdin_text, bun_stdout_write, bun_stderr_write, bun_exit };
 use prelude::{Some, None};
 
 extern type Bytes;
@@ -49,3 +49,14 @@ pub fn first_byte(path: String) -> Int {
   let value = readFileBytes(path);
   if bytesLength(value) == 0 { 0 } else { bytesByteAt(value, 0) }
 }
+
+/// Run `sh -c script` in `cwd` (empty string = inherit) and capture the result.
+pub fn run_captured(script: String, cwd: String) -> RunResult {
+  let dir = if cwd == "" { None } else { Some(cwd) };
+  bun_run_capture("sh", ["-c", script], dir)
+}
+
+/// Capture-run a program that does not exist, to exercise the spawn-error path.
+pub fn run_missing_program() -> RunResult {
+  bun_run_capture("affinescript-no-such-program", [], None)
+}

tests/codegen-bun/host_profile.harness.mjs

@@ -24,6 +24,19 @@ try {
     throw new Error("missing environment value failed");
   }
   if (subject.run_successful_child() !== 0) throw new Error("subprocess lowering failed");
+  // Captured run (bun_run_capture): planted controls with known answers.
+  const captured = subject.run_captured("echo hi; echo err >&2; exit 3", "");
+  if (captured.status !== 3) throw new Error(`capture status failed: ${captured.status}`);
+  if (captured.stdout !== "hi\n") throw new Error(`capture stdout failed: ${JSON.stringify(captured.stdout)}`);
+  if (captured.stderr !== "err\n") throw new Error(`capture stderr failed: ${JSON.stringify(captured.stderr)}`);
+  const inDir = subject.run_captured("pwd", nested);
+  if (inDir.status !== 0 || inDir.stdout.trim() !== nested) {
+    throw new Error(`capture cwd failed: ${JSON.stringify(inDir)}`);
+  }
+  const missing = subject.run_missing_program();
+  if (missing.status !== 1 || !missing.stderr.includes("affinescript-no-such-program")) {
+    throw new Error(`capture spawn-error failed: ${JSON.stringify(missing)}`);
+  }
   subject.remove_path(file);
   let missingPathThrew = false;
   try {