Add a tool to format changed files

This tool can be used prior to committing to format all changed files in
the repository to make sure it respect the coding style.

.gitmodules

@@ -61,3 +61,6 @@
 [submodule "lib/nanopb/nanopb"]
 	path = lib/nanopb/nanopb
 	url = https://github.com/nanopb/nanopb
+[submodule "coding-style"]
+	path = coding-style
+	url = https://github.com/cvra/coding-style

tools/format-diff.py

@@ -0,0 +1,100 @@
+#!/usr/bin/env python3
+"""
+Formats C/C++ files to the CVRA coding standard using uncrustify.
+"""
+
+import argparse
+import subprocess
+import os
+import shlex
+
+
+def repository_root():
+    toplevel = subprocess.check_output("git rev-parse --show-toplevel".split())
+    toplevel = toplevel.decode().rstrip()
+    return toplevel
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--all",
+        "-a",
+        help="Format all files (by default only changed files will be touched)",
+        action='store_true'
+    )
+
+    default_cfg = os.path.join(repository_root(), 'coding-style',
+                               'uncrustify.cfg')
+    parser.add_argument(
+        "--config",
+        "-c",
+        help="Config file for uncrustify",
+        type=argparse.FileType(),
+        default=default_cfg)
+
+    return parser.parse_args()
+
+
+def get_modified_files():
+    toplevel = repository_root()
+    cmd = "git diff --name-only".split()
+    modified_files = subprocess.check_output(cmd).decode()
+    modified_files += subprocess.check_output(cmd + ['--cached']).decode()
+
+    # Remove directories, as those are submodules
+    modified_files = [
+        m for m in modified_files.splitlines()
+        if not os.path.isdir(os.path.join(toplevel, m))
+    ]
+
+    return modified_files
+
+def get_all_files():
+    """
+    Returns a list of all files in the git repository.
+    """
+    cmd = "git ls-tree --full-tree --name-only -r HEAD".split()
+    files = subprocess.check_output(cmd).decode().splitlines()
+    return files
+
+
+def get_c_cpp_source(files):
+    """
+    Return a list of files matching C/C++ extensions.
+
+    >>> get_c_cpp_source(['a.txt', 'b.c', 'd.cpp', 'e.h', 'f.hpp'])
+    ['b.c', 'd.cpp', 'e.h', 'f.hpp']
+    """
+    allowed_extensions = ['.c', '.cpp', '.h', '.hpp']
+    return [f for f in files if os.path.splitext(f)[1] in allowed_extensions]
+
+
+def format_source(source_file, config):
+    cmd = "uncrustify -c {cfg} --replace --no-backup {f}"
+    cmd = cmd.format(cfg=config, f=source_file)
+    cmd = shlex.split(cmd)
+
+    # We have to run uncrustify twice because its parser sometimes cannot do
+    # single pass formatting
+    for _ in range(2):
+        subprocess.call(cmd)
+
+
+
+def main():
+    args = parse_args()
+
+    if args.all:
+        files = get_all_files()
+    else:
+        files = get_modified_files()
+
+    files = get_c_cpp_source(files)
+
+    for f in files:
+        format_source(f, args.config.name)
+
+
+if __name__ == '__main__':
+    main()