fix: support tmpdir: false when the out dir is inside the project dir

Node's fs.cp rejects copying a directory into a subdirectory of itself
before the copy filter runs, so packaging with tmpdir: false and an out
dir inside the project dir (e.g. Electron Forge's default ./out) failed
with ERR_FS_CP_EINVAL. When the staging path is inside the app dir, copy
each top-level entry individually instead, still applying the same
filter so ignored paths (including the out dir itself) are skipped.

Fixes #1679

Co-authored-by: ianho <anho.zhang@gmail.com>

Author: claude

src/platform.ts

@@ -183,11 +183,36 @@ export class App {
   async copyTemplate() {
     await runHooks(this.opts.beforeCopy, this.hookArgsWithOriginalResourcesAppDir);
 
-    await fs.promises.cp(this.opts.dir, this.originalResourcesAppDir, {
+    const filter = userPathFilter(this.opts)!;
+    const copyOpts = {
       recursive: true,
-      filter: userPathFilter(this.opts),
+      filter,
       dereference: typeof this.opts.derefSymlinks === 'boolean' ? this.opts.derefSymlinks : true,
-    });
+    };
+
+    const src = path.resolve(this.opts.dir);
+    const dest = path.resolve(this.originalResourcesAppDir);
+    const relativeDest = path.relative(src, dest);
+    if (
+      relativeDest &&
+      relativeDest !== '..' &&
+      !relativeDest.startsWith(`..${path.sep}`) &&
+      !path.isAbsolute(relativeDest)
+    ) {
+      // The destination is inside the app dir (e.g. tmpdir: false with the out dir
+      // inside the project dir). fs.cp rejects dest-inside-src before the filter runs,
+      // so copy each top-level entry individually instead.
+      await fs.promises.mkdir(dest, { recursive: true });
+      for (const entry of await fs.promises.readdir(src)) {
+        const srcEntry = path.join(src, entry);
+        const destEntry = path.join(dest, entry);
+        if (await filter(srcEntry, destEntry)) {
+          await fs.promises.cp(srcEntry, destEntry, copyOpts);
+        }
+      }
+    } else {
+      await fs.promises.cp(this.opts.dir, this.originalResourcesAppDir, copyOpts);
+    }
     await runHooks(this.opts.afterCopy, this.hookArgsWithOriginalResourcesAppDir);
     if (this.opts.prune) {
       await runHooks(this.opts.afterPrune, this.hookArgsWithOriginalResourcesAppDir);

test/packager.spec.ts

@@ -179,6 +179,33 @@ describe('packager', () => {
     expect(paths[0]).toBeDirectory();
   });
 
+  // https://github.com/electron/packager/issues/1679
+  it('can package with tmpdir disabled and the out dir inside the project dir', async ({
+    baseOpts,
+  }) => {
+    const projectDir = path.join(baseOpts.tmpdir as string, 'project');
+    await fs.promises.cp(baseOpts.dir, projectDir, { recursive: true });
+
+    const opts = {
+      ...baseOpts,
+      dir: projectDir,
+      out: path.join(projectDir, 'out'),
+      tmpdir: false,
+      asar: false,
+      platform: 'linux',
+      arch: 'x64',
+    } as const;
+
+    const paths = await packager(opts);
+    expect(paths).toHaveLength(1);
+    expect(paths[0]).toBeDirectory();
+
+    const appDir = path.join(paths[0], 'resources', 'app');
+    expect(path.join(appDir, 'main.js')).toBeFile();
+    // The out dir must not be copied into the packaged app
+    expect(fs.existsSync(path.join(appDir, 'out'))).toBe(false);
+  });
+
   it('preserves symlinks with derefSymlinks disabled', async ({ baseOpts }) => {
     const opts = {
       ...baseOpts,