Support GN build language

GN is a meta-build system that generates build files for Ninja
See also https://gn.googlesource.com/gn/

tests/languages/gn_test.py

@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+import re
+
+from pre_commit.languages import gn
+from testing.language_helpers import run_language
+
+
+def test_gn_format(tmp_path):
+    # Create a GN file with content that needs formatting
+    gn_file_content = """\
+source_set("hello_world") {
+    sources = [ "hello_world.cc", ]
+}
+"""
+    gn_file = tmp_path.joinpath('test.gn')
+    gn_file.write_text(gn_file_content)
+
+    # Run gn format on the created file
+    ret, out = run_language(tmp_path, gn, f'gn format {gn_file}')
+
+    # Read the formatted file
+    formatted_content = gn_file.read_text()
+
+    assert ret == 0
+    assert gn_file_content != formatted_content
+
+
+def test_gn_version(tmp_path):
+    ret, out = run_language(
+        tmp_path,
+        gn,
+        'gn --version',
+    )
+    assert ret == 0
+    version_regex = re.compile(rb'\d+ \([a-f0-9]+\)\n')
+    assert version_regex.search(out) is not None