1 files changed, 63 insertions, 0 deletions
diff --git a/comm/taskcluster/comm_taskgraph/transforms/source_test.py b/comm/taskcluster/comm_taskgraph/transforms/source_test.py
new file mode 100644
index 0000000000..d4ae39c134
--- /dev/null
+++ b/comm/taskcluster/comm_taskgraph/transforms/source_test.py
@@ -0,0 +1,63 @@
+# 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 http://mozilla.org/MPL/2.0/.
+
+import logging
+import shlex
+
+from taskgraph.transforms.base import TransformSequence
+from taskgraph.util.path import join as join_path
+from taskgraph.util.path import match as match_path
+
+from gecko_taskgraph.files_changed import get_changed_files
+
+logger = logging.getLogger(__name__)
+
+transforms = TransformSequence()
+
+
+def get_patterns(job):
+    """Get the "run on-changed" file patterns."""
+    optimization = job.get("optimization", {})
+    if optimization:
+        return optimization.copy().popitem()[1]
+    return []
+
+
+def shlex_join(split_command):
+    """shlex.join from Python 3.8+"""
+    return " ".join(shlex.quote(arg) for arg in split_command)
+
+
+@transforms.add
+def changed_clang_format(config, jobs):
+    """
+    Transform for clang-format job to set the commandline to only check
+    C++ files that were changed in the current push rather than running on
+    the entire repository.
+    """
+    for job in jobs:
+        if job.get("name", "") == "clang-format":
+            repository = config.params.get("comm_head_repository")
+            revision = config.params.get("comm_head_rev")
+
+            match_patterns = get_patterns(job)
+            changed_files = {
+                join_path("comm", file) for file in get_changed_files(repository, revision)
+            }
+
+            cpp_files = []
+            for pattern in match_patterns:
+                for path in changed_files:
+                    if match_path(path, pattern):
+                        cpp_files.append(path)
+
+            # In the event that no C/C++ files were changed in the current push,
+            # the commandline will end up being invalid. But, the clang-format
+            # job will get dropped by optimization, so it doesn't really matter.
+            if cpp_files:
+                job["run"]["command"] = job["run"]["command"].format(
+                    changed_files=shlex_join(cpp_files)
+                )
+
+        yield job