node:child_process: validate command, file, and args inputs #3079

Summary

node:child_process setup should reject invalid command/file and args inputs before attempting to run a process. Perry currently treats missing commands as empty output or null results, and treats non-array args values as an empty args list, diverging from Node's ERR_INVALID_ARG_TYPE behavior.

Expected Node behavior

Local Node v25.9.0 probe:

const cp = require("node:child_process");
for (const [label, fn] of [
  ["exec missing", () => cp.exec()],
  ["exec number", () => cp.exec(123)],
  ["execSync missing", () => cp.execSync()],
  ["execSync number", () => cp.execSync(123)],
  ["execFile missing", () => cp.execFile()],
  ["execFile number file", () => cp.execFile(123)],
  ["execFile args string", () => cp.execFile("sh", "-c")],
  ["execFileSync missing", () => cp.execFileSync()],
  ["execFileSync args string", () => cp.execFileSync("sh", "-c")],
  ["spawnSync missing", () => cp.spawnSync()],
  ["spawnSync number", () => cp.spawnSync(123)],
  ["spawnSync args string", () => cp.spawnSync("sh", "-c")],
]) {
  try { fn(); console.log(label, "OK"); }
  catch (e) { console.log(label, e.name, e.code); }
}

Node throws TypeError ERR_INVALID_ARG_TYPE for missing/non-string command / file inputs and for non-object/non-array args values such as a string.

Current Perry evidence

• crates/perry-runtime/src/child_process/mod.rs::js_child_process_exec() returns empty stdout (and optionally invokes the callback with no error) when cmd_ptr is null.
• js_child_process_exec_sync() returns an empty Buffer/string when cmd_ptr is null.
• js_child_process_spawn_sync() returns a null pointer when cmd_ptr is null instead of throwing.
• js_child_process_exec_file() and js_child_process_exec_file_sync() call cp_read_string_header(file_ptr), and cp_read_string_header() maps 0 to an empty string.
• cp_args_from_value() and cp_read_arg_strings() silently turn missing/non-array args into an empty vector and skip non-string entries, so execFileSync("sh", "-c") / spawnSync("sh", "-c") do not get Node's setup-time args validation.

Suggested test surface

• Add child_process parity tests for missing/non-string command/file values across exec, execSync, execFile, execFileSync, and spawnSync.
• Add non-array args tests for execFile, execFileSync, and spawnSync, especially string args.
• Assert synchronous TypeError with ERR_INVALID_ARG_TYPE before any child process is launched.

Scope / non-goals

• Scoped to setup-time command/file/args validation for implemented child_process APIs.
• Does not cover broader option semantics such as stdio, timeout, maxBuffer, input, killSignal, or AbortSignal, which are tracked by node:child_process: honor spawn and exec option semantics beyond cwd/env/shell #2555.
• Does not cover subprocess lifecycle disposal (node:child_process: implement subprocess[Symbol.dispose] lifecycle method #2556) or IPC bootstrap helpers (node:child_process: expose _forkChild IPC bootstrap helper #2717).

Duplicate search

• child_process command args validation ERR_INVALID_ARG_TYPE
• child_process spawnSync execFileSync execSync validation options
• PR search: child_process command args validation ERR_INVALID_ARG_TYPE

Search found #2555 for broader option semantics but no issue covering command/file/args input validation.