ninja: error if trying to build for use_remoteexec=true

Change-Id: Ia32dd3cba1d1874401c6614f792f212b2cfa60a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5660200
Commit-Queue: Joanna Wang <jojwang@chromium.org>
Reviewed-by: Junji Watanabe <jwata@google.com>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Joanna Wang <jojwang@chromium.org>

gn_helper.py

@@ -0,0 +1,60 @@
+# Copyright 2024 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""This provides an easy way to access args.gn."""
+
+import os
+import re
+
+
+def _gn_lines(output_dir, path):
+    """
+    Generator function that returns args.gn lines one at a time, following
+    import directives as needed.
+    """
+    import_re = re.compile(r'\s*import\("(.*)"\)')
+    with open(path, encoding="utf-8") as f:
+        for line in f:
+            match = import_re.match(line)
+            if match:
+                raw_import_path = match.groups()[0]
+                if raw_import_path[:2] == "//":
+                    import_path = os.path.normpath(
+                        os.path.join(output_dir, "..", "..",
+                                     raw_import_path[2:]))
+                else:
+                    import_path = os.path.normpath(
+                        os.path.join(os.path.dirname(path), raw_import_path))
+                yield from _gn_lines(output_dir, import_path)
+            else:
+                yield line
+
+
+def _path(output_dir):
+    return os.path.join(output_dir, "args.gn")
+
+
+def exists(output_dir):
+    """Checks args.gn exists in output_dir."""
+    return os.path.exists(_path(output_dir))
+
+
+def lines(output_dir):
+    """Generator of args.gn lines. comment is removed."""
+    if not exists(output_dir):
+        return
+    for line in _gn_lines(output_dir, _path(output_dir)):
+        line_without_comment = line.split("#")[0]
+        yield line_without_comment
+
+
+_gn_arg_pattern = re.compile(r"(^|\s)([^=\s]*)\s*=\s*(\S*)\s*$")
+
+
+def args(output_dir):
+    """Generator of args.gn's key,value pair."""
+    for line in lines(output_dir):
+        m = _gn_arg_pattern.match(line)
+        if not m:
+            continue
+        yield (m.group(2), m.group(3))