gn_helpers: support absolute path import

There is a case that args.gn imports from absolute path.

Bug: 393209409
Change-Id: I90def7633bb8a937f27fea96fc5d4629153e4f94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6210737
Commit-Queue: Richard Wang <richardwa@google.com>
Auto-Submit: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Richard Wang <richardwa@google.com>
Cr-Commit-Position: refs/heads/main@{#1413282}

build/gn_helpers.py

@@ -32,7 +32,7 @@ _CHROMIUM_ROOT = os.path.abspath(
 
 ARGS_GN_FILENAME = 'args.gn'
 BUILD_VARS_FILENAME = 'build_vars.json'
-IMPORT_RE = re.compile(r'^import\("//(\S+)"\)')
+IMPORT_RE = re.compile(r'^import\("(\S+)"\)')
 
 
 class GNError(Exception):
@@ -287,7 +287,20 @@ class GNValueParser(object):
       regex_match = IMPORT_RE.match(line)
       if not regex_match:
         raise GNError('Not a valid import string: %s' % line)
-      import_path = os.path.join(self.checkout_root, regex_match.group(1))
+      import_path = regex_match.group(1)
+
+      if import_path.startswith("//"):
+        import_path = os.path.join(self.checkout_root, import_path[2:])
+      elif sys.platform.startswith('win32'):
+        if import_path.startswith("/"):
+          # gn users '/C:/path/to/foo.gn', not 'C:/path/to/foo.gn' on windows
+          import_path = import_path[1:]
+        else:
+          raise GNError('Need /-prefix for an absolute path: %s' % import_path)
+
+      if not os.path.isabs(import_path):
+        raise GNError('Unable to use relative path in import path: %s' %
+                      import_path)
       with open(import_path) as f:
         imported_args = f.read()
       self.input = self.input.replace(line, imported_args)

build/gn_helpers_unittest.py

@@ -315,6 +315,29 @@ class UnitTest(unittest.TestCase):
           textwrap.dedent('import("some/relative/args/file.gni")'))
       parser.ReplaceImports()
 
+    if sys.platform.startswith('win32'):
+      parser = gn_helpers.GNValueParser(
+          textwrap.dedent("""
+          some_arg1 = "val1"
+          import("/c:/some/args/file.gni")
+          some_arg2 = "val2"
+          """))
+      with mock.patch(open_fun, mock.mock_open(read_data=fake_import)):
+        parser.ReplaceImports()
+      self.assertEqual(
+          parser.input,
+          textwrap.dedent("""
+          some_arg1 = "val1"
+          some_imported_arg = "imported_val"
+          some_arg2 = "val2"
+          """))
+
+      # A path that's not source absolute should raise an exception.
+      with self.assertRaises(gn_helpers.GNError):
+        parser = gn_helpers.GNValueParser(
+            textwrap.dedent('import("c:/some/args/file.gni")'))
+        parser.ReplaceImports()
+
   def test_CreateBuildCommand(self):
     with tempfile.TemporaryDirectory() as temp_dir:
       suffix = '.bat' if sys.platform.startswith('win32') else ''