tools/codeformat: By default only check/update on current git branch.

It can be difficult using the codeformat.py tool when there are other files
in the repository not currently matching the standard.

For developers, running over the entire repo can throw up a large list of
changes in a local git which can lead to inclusion of unrelated changes in
commits if they're added accidentally.  If the files arg is used to trim
down the list of files scanned, it runs a risk of missing some files
they've modified.  In CI, it means that PR's can fail on codeformat for
issues that aren't related to that PR.

This change adds a git query in the codeformat tool by default to only work
on the list of files that have been modified in the current branch.  This
can still be overridden by the files arg to run over all files still, eg.
python3 tools/codeformat.py -v '**'.

tools/codeformat.py

@@ -54,6 +54,10 @@ C_EXTS = (
 PY_EXTS = (".py",)
 
 
+MAIN_BRANCH = "master"
+BASE_BRANCH = os.environ.get("GITHUB_BASE_REF", MAIN_BRANCH)
+
+
 def list_files(paths, exclusions=None, prefix=""):
     files = set()
     for pattern in paths:
@@ -105,12 +109,58 @@ def fixup_c(filename):
         assert not dedent_stack, filename
 
 
+def query_git_files(verbose):
+    def cmd_result_set(cmd):
+        ret = subprocess.run(cmd, capture_output=True).stdout.strip().decode()
+        if not ret:
+            return set()
+        return {f.strip() for f in ret.split("\n")}
+
+    try:
+        ret = set()
+
+        # Check locally modified files
+        dirty = cmd_result_set(["git", "status", "--porcelain"])
+        ret = {line.split(" ", 1)[-1] for line in dirty}
+
+        # Current commit and branch
+        current_commit = (
+            subprocess.run(["git", "rev-parse", "HEAD"], capture_output=True)
+            .stdout.strip()
+            .decode()
+        )
+        current_branches = cmd_result_set(["git", "branch", "--contains", current_commit])
+        if MAIN_BRANCH in current_branches:
+            if ret:
+                if verbose:
+                    print("Local changes detected, only scanning them.")
+                return ret
+
+            # We're on clean master, run on entire repo
+            if verbose:
+                print("Scanning whole repository")
+            return None
+
+        # List the files modified on current branch
+        if verbose:
+            print("Scanning changes from current branch and any local changes")
+        ret |= cmd_result_set(["git", "diff", "--relative", "--name-only", BASE_BRANCH])
+        return ret
+    except:
+        # Git not available, run on entire repo
+        return None
+
+
 def main():
     cmd_parser = argparse.ArgumentParser(description="Auto-format C and Python files.")
     cmd_parser.add_argument("-c", action="store_true", help="Format C code only")
     cmd_parser.add_argument("-p", action="store_true", help="Format Python code only")
     cmd_parser.add_argument("-v", action="store_true", help="Enable verbose output")
-    cmd_parser.add_argument("files", nargs="*", help="Run on specific globs")
+    cmd_parser.add_argument(
+        "files",
+        nargs="*",
+        help="Run on specific globs. If not specied current branch changes will be used",
+    )
     args = cmd_parser.parse_args()
 
     # Setting only one of -c or -p disables the other. If both or neither are set, then do both.
@@ -122,7 +172,9 @@ def main():
     if args.files:
         files = list_files(args.files)
     else:
-        files = list_files(PATHS, EXCLUSIONS, TOP)
+        files = query_git_files(verbose=args.v)
+        if not files:
+            files = list_files(PATHS, EXCLUSIONS, TOP)
 
     # Extract files matching a specific language.
     def lang_files(exts):