Adding clangd-tidy-diff script for lintings of source control deltas

Inspired by clang-tidy-diff script from the llvm project (https://clang.llvm.org/extra/doxygen/clang-tidy-diff_8py_source.html).
This enables a CI check of only the changes lines

clangd_tidy/__init__.py

@@ -1,4 +1,5 @@
+from .clangd_tidy_diff_cli import clang_tidy_diff
 from .main_cli import main_cli
 from .version import __version__
 
-__all__ = ["main_cli", "__version__"]
+__all__ = ["main_cli", "clang_tidy_diff", "__version__"]

clangd_tidy/clangd_tidy_diff_cli.py

@@ -0,0 +1,91 @@
+"""
+Receives a diff on stdin and runs clangd-tidy only on the changed lines.
+This is useful to slowly onboard a codebase to linting or to find regressions.
+Inspired by clang-tidy-diff.py from the LLVM project.
+
+Example usage with git:
+    git diff -U0 HEAD^^..HEAD | clangd-tidy-diff -p my/build
+"""
+
+import argparse
+import json
+import re
+import subprocess
+import sys
+
+from .version import __version__
+
+ADDED_FILE_NAME_REGEX = re.compile(r'^\+\+\+ "?(?P<prefix>.*?/)(?P<file>[^\s"]*)')
+ADDED_LINES_REGEX = re.compile(r"^@@.*\+(?P<line>\d+)(,(?P<count>\d+))?")
+
+
+def clang_tidy_diff():
+    parser = argparse.ArgumentParser(
+        description="Runs clangd-tidy against modified files,"
+        " and returns diagnostics only on changed lines."
+    )
+    parser.add_argument(
+        "-V", "--version", action="version", version=f"%(prog)s {__version__}"
+    )
+    parser.add_argument(
+        "-p",
+        "--compile-commands-dir",
+        help="Specify a path to look for compile_commands.json. If the path is invalid, clangd-tidy will look in the current directory and parent paths of each source file.",
+    )
+    parser.add_argument(
+        "--pass-arg",
+        action="append",
+        help="Pass this argument to clangd-tidy (can be used multiple times)",
+    )
+    args = parser.parse_args()
+
+    last_file = None
+    lines_per_file = {}
+    for line in sys.stdin:
+        m = re.search(ADDED_FILE_NAME_REGEX, line)
+        if m:
+            last_file = m.group("file")
+
+        if last_file is None:
+            continue
+
+        m = re.search(ADDED_LINES_REGEX, line)
+        if m is None:
+            continue
+
+        start_line = int(m.group("line"))
+        line_count = 1
+        if m.group("count") is not None:
+            line_count = int(m.group("count"))
+        if line_count == 0:
+            continue
+
+        end_line = start_line + line_count - 1
+        lines_per_file.setdefault(last_file, []).append([start_line, end_line])
+
+    if len(lines_per_file) == 0:
+        print("No relevant changes found.")
+        sys.exit(0)
+
+    filters = []
+    for file, lines in lines_per_file.items():
+        filters.append({"name": file, "lines": lines})
+
+    filters_json = json.dumps(filters)
+    command = ["clangd-tidy", "--line-filter", filters_json]
+
+    if args.compile_commands_dir:
+        command.extend(["--compile-commands-dir", args.compile_commands_dir])
+
+    if args.pass_arg:
+        command.extend(args.pass_arg)
+
+    files = list(lines_per_file.keys())
+    command.append("--")
+    command.extend(files)
+
+    sys.exit(subprocess.run(command).returncode)
+
+
+if __name__ == "__main__":
+    clang_tidy_diff()

pyproject.toml

@@ -23,6 +23,7 @@ classifiers = [
 
 [project.scripts]
 clangd-tidy = "clangd_tidy:main_cli"
+clangd-tidy-diff = "clangd_tidy:clang_tidy_diff"
 
 [project.urls]
 "Homepage" = "https://github.com/lljbash/clangd-tidy"