Add presubmit to check for exact imports.

Author: goodov

build/commands/PRESUBMIT.py

@@ -0,0 +1,53 @@
+# Copyright (c) 2026 The Brave Authors. All rights reserved.
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at https://mozilla.org/MPL/2.0/.
+
+import os
+import re
+
+PRESUBMIT_VERSION = '2.0.0'
+
+
+def CheckImportSpecifierMatchesFile(input_api, output_api):
+    """Checks that relative import specifier matches the actual file on disk.
+
+    When running TypeScript natively via Node.js (no transpilation), imports
+    must use the real file extension. For example, if a file is named config.ts,
+    importing it as './config.js' is an error.
+    """
+
+    IMPORT_RE = re.compile(
+        r'''
+            (?:
+                \bfrom \s+      # static: import/export ... from
+              | import \s* \(   # dynamic: import(
+            )
+            \s* ['"]
+            ( \. [^'"]+ \. (?:[cm]?[jt]s) )  # relative specifier with extension
+            ['"]
+        ''', re.VERBOSE)
+
+    files_to_check = (r'.+\.[cm]?[jt]s$', )
+    file_filter = lambda f: input_api.FilterSourceFile(
+        f, files_to_check=files_to_check)
+
+    items = []
+    for f in input_api.AffectedSourceFiles(file_filter):
+        file_dir = os.path.dirname(f.AbsoluteLocalPath())
+        for lineno, line in enumerate(f.NewContents(), 1):
+            for match in IMPORT_RE.finditer(line):
+                specifier = match.group(1)
+                resolved = os.path.normpath(os.path.join(file_dir, specifier))
+
+                if not os.path.isfile(resolved):
+                    items.append(f'{f.LocalPath()}:{lineno}: '
+                                 f'file not found: {specifier}')
+
+    if not items:
+        return []
+
+    return [
+        output_api.PresubmitError(
+            'Import specifier must match the actual file on disk.', items)
+    ]