Fix Windows pnpm process spawning

Author: Spencer

scripts/shared/process.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { isDirectExecution, resolveSpawnCommand } from "./process.js";
+import { isDirectExecution, resolveSpawnCommand, shouldUseShellForCommand } from "./process.js";
 
 describe("isDirectExecution", () => {
   it("matches direct execution for POSIX script paths", () => {
@@ -18,8 +18,8 @@ describe("isDirectExecution", () => {
 });
 
 describe("resolveSpawnCommand", () => {
-  it("uses pnpm.cmd on Windows so spawn works without a shell", () => {
-    expect(resolveSpawnCommand("pnpm", "win32")).toBe("pnpm.cmd");
+  it("keeps pnpm unresolved on Windows so cmd can resolve the shim", () => {
+    expect(resolveSpawnCommand("pnpm", "win32")).toBe("pnpm");
   });
 
   it("does not rewrite native Windows executables like git", () => {
@@ -30,3 +30,17 @@ describe("resolveSpawnCommand", () => {
     expect(resolveSpawnCommand("pnpm", "linux")).toBe("pnpm");
   });
 });
+
+describe("shouldUseShellForCommand", () => {
+  it("uses a shell for pnpm on Windows because pnpm.cmd is not directly executable", () => {
+    expect(shouldUseShellForCommand("pnpm", "win32")).toBe(true);
+  });
+
+  it("does not use a shell for native executables like git on Windows", () => {
+    expect(shouldUseShellForCommand("git", "win32")).toBe(false);
+  });
+
+  it("does not use a shell on POSIX platforms", () => {
+    expect(shouldUseShellForCommand("pnpm", "linux")).toBe(false);
+  });
+});

scripts/shared/process.ts

@@ -2,7 +2,7 @@
  * Process utilities for running child processes
  */
 
-import { type ChildProcess, spawn } from "child_process";
+import { type ChildProcess, type SpawnOptions, spawn } from "child_process";
 import { posix, resolve } from "path";
 
 export interface ProcessOptions {
@@ -11,6 +11,12 @@ export interface ProcessOptions {
   stdio?: "inherit" | "pipe" | "ignore";
 }
 
+interface SpawnConfig {
+  command: string;
+  options: ProcessOptions;
+  platform?: NodeJS.Platform;
+}
+
 const WINDOWS_CMD_SHIMS = new Set(["pnpm", "npm", "npx"]);
 
 function isWindowsDrivePath(path: string): boolean {
@@ -75,13 +81,29 @@ export function isDirectExecution(moduleUrl: string, argv1: string | undefined =
 
 export function resolveSpawnCommand(
   command: string,
-  platform: NodeJS.Platform = process.platform
+  _platform: NodeJS.Platform = process.platform
 ): string {
-  if (platform !== "win32") {
-    return command;
-  }
+  return command;
+}
 
-  return WINDOWS_CMD_SHIMS.has(command.toLowerCase()) ? `${command}.cmd` : command;
+export function shouldUseShellForCommand(
+  command: string,
+  platform: NodeJS.Platform = process.platform
+): boolean {
+  return platform === "win32" && WINDOWS_CMD_SHIMS.has(command.toLowerCase());
+}
+
+function createSpawnOptions({
+  command,
+  options,
+  platform = process.platform,
+}: SpawnConfig): SpawnOptions {
+  return {
+    cwd: options.cwd,
+    env: options.env ?? process.env,
+    stdio: options.stdio ?? "inherit",
+    shell: shouldUseShellForCommand(command, platform),
+  };
 }
 
 /**
@@ -93,12 +115,11 @@ export function run(
   options: ProcessOptions = {}
 ): Promise<void> {
   return new Promise((resolve, reject) => {
-    const child = spawn(resolveSpawnCommand(command), args, {
-      cwd: options.cwd,
-      env: options.env ?? process.env,
-      stdio: options.stdio ?? "inherit",
-      shell: false,
-    });
+    const child = spawn(
+      resolveSpawnCommand(command),
+      args,
+      createSpawnOptions({ command, options })
+    );
 
     child.on("close", (code) => {
       if (code === 0) {
@@ -122,12 +143,7 @@ export function runBackground(
   args: string[] = [],
   options: ProcessOptions = {}
 ): ChildProcess {
-  const child = spawn(resolveSpawnCommand(command), args, {
-    cwd: options.cwd,
-    env: options.env ?? process.env,
-    stdio: options.stdio ?? "inherit",
-    shell: false,
-  });
+  const child = spawn(resolveSpawnCommand(command), args, createSpawnOptions({ command, options }));
 
   return child;
 }