Add (optional) post-commit git hook for running bootstrap script (#22632)

Once installed this script will automatically bootstrap emscripten on
each branch checkout.

Use `./bootstrap -i/--install-post-checkout` to install the script. We
could consider doing this automatically too as a followup if folks end
up liking this solution.

Fixes: #22550

Author: sbc100

bootstrap.py

@@ -57,8 +57,21 @@ def main(args):
   parser = argparse.ArgumentParser(description=__doc__)
   parser.add_argument('-v', '--verbose', action='store_true', help='verbose', default=False)
   parser.add_argument('-n', '--dry-run', action='store_true', help='dry run', default=False)
+  parser.add_argument('-i', '--install-post-checkout', action='store_true', help='install post checkout script', default=False)
   args = parser.parse_args()
 
+  if args.install_post_checkout:
+    if not os.path.exists(utils.path_from_root('.git')):
+      print('--install-post-checkout requires git checkout')
+      return 1
+
+    src = utils.path_from_root('tools/maint/post-checkout')
+    dst = utils.path_from_root('.git/hooks')
+    if not os.path.exists(dst):
+      os.mkdir(dst)
+    shutil.copy(src, dst)
+    return 0
+
   for name, deps, cmd in actions:
     if check_deps(name, deps):
       print('Up-to-date: %s' % name)
@@ -67,11 +80,12 @@ def main(args):
     stamp_file = get_stamp_file(name)
     if args.dry_run:
       print(' (skipping: dry run) -> %s' % ' '.join(cmd))
-      return
+      continue
     print(' -> %s' % ' '.join(cmd))
     shared.run_process(cmd, cwd=utils.path_from_root())
     utils.safe_ensure_dirs(STAMP_DIR)
     utils.write_file(stamp_file, 'Timestamp file created by bootstrap.py')
+  return 0
 
 
 if __name__ == '__main__':

tools/maint/post-checkout

@@ -0,0 +1,11 @@
+#!/bin/sh
+#
+# Git post-checkout script that takes care of running emscirpten's
+# bootstrap script when changing branches.
+#
+# The bootstrap script itself is smart enough to basically do nothing unless
+# one of the relevant files was updated (e.g. package.json).
+
+# Test for the existence of the bootstrap script itself to handle branches
+# that predate its existence.
+test -f ./bootstrap && exec ./bootstrap