build: Add script to check code style

Borrowed from Tracker, this script has different mode usages:
* --sha allows specifying a commit SHA, HEAD^ by default.
* --dry-run shows suggested changes in stdout, by default
  the local tree is changed.
* --rewrite amends the last commit, in addition to performing
  the changes.

This allows from simple style checks in the development tree,
automatically rewriting with the suggested changes (e.g. with
`git rebase --exec ./check-style -r`) and CI integration.

The script has per-function granularity, and works by re-styling
individually every commit, and inside every commit every chunk.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1924>

check-style.py

@@ -0,0 +1,134 @@
+#!/bin/env python3
+
+import argparse
+import os
+import re
+import subprocess
+import sys
+import tempfile
+
+# Path relative to this script
+uncrustify_cfg = 'tools/uncrustify.cfg'
+
+def run_diff(sha):
+    proc = subprocess.Popen(["git", "diff", "-U0", "--function-context", sha, "HEAD"], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    files = proc.stdout.read().strip().decode('utf-8')
+    return files.split('\n')
+
+def find_chunks(diff):
+    file_entry_re = re.compile('^\+\+\+ b/(.*)$')
+    diff_chunk_re = re.compile('^@@ -\d+,\d+ \+(\d+),(\d+)')
+    file = None
+    chunks = []
+
+    for line in diff:
+        match = file_entry_re.match(line)
+        if match:
+            file = match.group(1)
+
+        match = diff_chunk_re.match(line)
+        if match:
+            start = int(match.group(1))
+            len = int(match.group(2))
+            end = start + len
+
+            if len > 0 and (file.endswith('.c') or file.endswith('.h') or file.endswith('.vala')):
+                chunks.append({ 'file': file, 'start': start, 'end': end })
+
+    return chunks
+
+def reformat_chunks(chunks, rewrite):
+    # Creates temp file with INDENT-ON/OFF comments
+    def create_temp_file(file, start, end):
+        with open(file) as f:
+            tmp = tempfile.NamedTemporaryFile()
+            tmp.write(b'/** *INDENT-OFF* **/\n')
+            for i, line in enumerate(f):
+                if i == start - 2:
+                    tmp.write(b'/** *INDENT-ON* **/\n')
+
+                tmp.write(bytes(line, 'utf-8'))
+
+                if i == end - 2:
+                    tmp.write(b'/** *INDENT-OFF* **/\n')
+
+            tmp.seek(0)
+
+        return tmp
+
+    # Removes uncrustify INDENT-ON/OFF helper comments
+    def remove_indent_comments(output):
+        tmp = tempfile.NamedTemporaryFile()
+
+        for line in output:
+            if line != b'/** *INDENT-OFF* **/\n' and line != b'/** *INDENT-ON* **/\n':
+                tmp.write(line)
+
+        tmp.seek(0)
+
+        return tmp
+
+    changed = None
+
+    for chunk in chunks:
+        # Add INDENT-ON/OFF comments
+        tmp = create_temp_file(chunk['file'], chunk['start'], chunk['end'])
+
+        # uncrustify chunk
+        proc = subprocess.Popen(["uncrustify", "-c", uncrustify_cfg, "-f", tmp.name], stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
+        reindented = proc.stdout.readlines()
+        tmp.close()
+
+        # Remove INDENT-ON/OFF comments
+        formatted = remove_indent_comments(reindented)
+
+        if dry_run is True:
+            # Show changes
+            proc = subprocess.Popen(["diff", "-up", "--color=always", chunk['file'], formatted.name], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+            diff = proc.stdout.read().decode('utf-8')
+            if diff != '':
+                output = re.sub('\t', '↦\t', diff)
+                print(output)
+                changed = True
+        else:
+            # Apply changes
+            diff = subprocess.Popen(["diff", "-up", chunk['file'], formatted.name], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+            patch = subprocess.Popen(["patch", chunk['file']], stdin=diff.stdout)
+            diff.stdout.close()
+            patch.communicate()
+
+        formatted.close()
+
+    return changed
+
+
+parser = argparse.ArgumentParser(description='Check code style.')
+parser.add_argument('--sha', metavar='SHA', type=str,
+                    help='SHA for the commit to compare HEAD with')
+parser.add_argument('--dry-run', '-d', type=bool,
+                    action=argparse.BooleanOptionalAction,
+                    help='Only print changes to stdout, do not change code')
+parser.add_argument('--rewrite', '-r', type=bool,
+                    action=argparse.BooleanOptionalAction,
+                    help='Whether to amend the result to the last commit (e.g. \'git rebase --exec "%(prog)s -r"\')')
+
+# Change CWD to script location, necessary for always locating the configuration file
+os.chdir(os.path.dirname(os.path.abspath(sys.argv[0])))
+
+args = parser.parse_args()
+sha = args.sha or 'HEAD^'
+rewrite = args.rewrite
+dry_run = args.dry_run
+
+diff = run_diff(sha)
+chunks = find_chunks(diff)
+changed = reformat_chunks(chunks, rewrite)
+
+if dry_run is not True and rewrite is True:
+    proc = subprocess.Popen(["git", "commit", "--all", "--amend", "-C", "HEAD"], stdout=subprocess.DEVNULL)
+    os._exit(0)
+elif dry_run is True and changed is True:
+    print ("\nIssue the following command in your local tree to apply the suggested changes (needs uncrustify installed):\n\n $ git rebase origin/master --exec \"./check-style.py -r\" \n")
+    os._exit(-1)
+
+os._exit(0)