Add support for passing a response file to file_packager (#24107)

Because calls to `file_packager` go through the shell wrapper, this can
on Windows due to a "command line is too long" error (e.g. with a long
list of `--preload-file`), even if a response file was provided to
`emcc` in order avoid the issue.

Fix it by supporting response files in `file_packager`, and changing
`link` so that it uses a response file where needed.

Author: iscgar

test/test_other.py

@@ -3746,6 +3746,22 @@ def clean(txt):
 
     self.assertTextDataIdentical(clean(proc.stdout), clean(proc2.stdout))
 
+  def test_file_packager_response_file(self):
+    filenames = [f'foo.{i:032}' for i in range(4096)]
+
+    create_file('src.c', 'int main() { return 0; }\n')
+    create_file('data.txt', '')
+
+    response_data = '\n'.join(f'--preload-file data.txt@{f}' for f in filenames)
+    self.assertGreater(len(response_data), (1 << 16))
+    create_file('data.rsp', response_data)
+
+    self.run_process([EMCC, 'src.c', '@data.rsp'])
+    data = read_file('a.out.js')
+
+    for f in filenames:
+      self.assertTrue(f'"/{f}"' in data)
+
   def test_file_packager_separate_metadata(self):
     # verify '--separate-metadata' option produces separate metadata file
     ensure_dir('subdir')

tools/file_packager.py

@@ -84,6 +84,7 @@
 sys.path.insert(0, __rootdir__)
 
 from tools import shared, utils, js_manipulation
+from tools.response_file import substitute_response_files
 
 
 DEBUG = os.environ.get('EMCC_DEBUG')
@@ -368,12 +369,18 @@ def main():  # noqa: C901, PLR0912, PLR0915
   See the source for more details.''')
     return 1
 
-  data_target = sys.argv[1]
+  # read response files very early on
+  try:
+    args = substitute_response_files(sys.argv[1:])
+  except IOError as e:
+    shared.exit_with_error(e)
+
+  data_target = args[0]
   data_files = []
   plugins = []
   leading = ''
 
-  for arg in sys.argv[2:]:
+  for arg in args[1:]:
     if arg == '--preload':
       leading = 'preload'
     elif arg == '--embed':

tools/link.py

@@ -3067,7 +3067,8 @@ def package_files(options, target):
     file_args += ['--obj-output=' + object_file]
     rtn.append(object_file)
 
-  cmd = [shared.FILE_PACKAGER, shared.replace_suffix(target, '.data')] + file_args
+  cmd = building.get_command_with_possible_response_file(
+    [shared.FILE_PACKAGER, shared.replace_suffix(target, '.data')] + file_args)
   if options.preload_files:
     # Preloading files uses --pre-js code that runs before the module is loaded.
     file_code = shared.check_call(cmd, stdout=PIPE).stdout