[Workflow] Add new code format helper.

.github/workflows/pr-code-format.yml

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+name: "Check code formatting"
+on: pull_request
+permissions:
+  pull-requests: write
+
+jobs:
+  code_formatter:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Fetch LLVM sources
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+          fetch-depth: 2
+
+      - name: Get changed files
+        id: changed-files
+        uses: tj-actions/changed-files@v39
+        with:
+          separator: ","
+
+      - name: "Listed files"
+        run: |
+          echo "Formatting files:"
+          echo "${{ steps.changed-files.outputs.all_changed_files }}"
+
+      - name: Install clang-format
+        uses: aminya/setup-cpp@v1
+        with:
+          clangformat: 16.0.6
+
+      - name: Setup Python env
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+          cache: 'pip'
+          cache-dependency-path: 'llvm/utils/git/requirements_formatting.txt'
+
+      - name: Install python dependencies
+        run: pip install -r llvm/utils/git/requirements_formatting.txt
+
+      - name: Run code formatter
+        env:
+          GITHUB_PR_NUMBER: ${{ github.event.pull_request.number }}
+          START_REV: ${{ github.event.pull_request.base.sha }}
+          END_REV: ${{ github.event.pull_request.head.sha }}
+          CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}
+        run: |
+          python llvm/utils/git/code-format-helper.py \
+            --token ${{ secrets.GITHUB_TOKEN }} \
+            --issue-number $GITHUB_PR_NUMBER \
+            --start-rev $START_REV \
+            --end-rev $END_REV \
+            --changed-files "$CHANGED_FILES"

llvm/utils/git/code-format-helper.py

@@ -0,0 +1,236 @@
+#!/usr/bin/env python3
+#
+# ====- code-format-helper, runs code formatters from the ci --*- python -*--==#
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# ==-------------------------------------------------------------------------==#
+
+import argparse
+import os
+import subprocess
+import sys
+from functools import cached_property
+
+import github
+from github import IssueComment, PullRequest
+
+
+class FormatHelper:
+    COMMENT_TAG = "<!--LLVM CODE FORMAT COMMENT: {fmt}-->"
+    name = "unknown"
+
+    @property
+    def comment_tag(self) -> str:
+        return self.COMMENT_TAG.replace("fmt", self.name)
+
+    def format_run(self, changed_files: [str], args: argparse.Namespace) -> str | None:
+        pass
+
+    def pr_comment_text(self, diff: str) -> str:
+        return f"""
+{self.comment_tag}
+
+:warning: {self.friendly_name}, {self.name} found issues in your code. :warning:
+
+<details>
+<summary>
+You can test this locally with the following command:
+</summary>
+
+``````````bash
+{self.instructions}
+``````````
+
+</details>
+
+<details>
+<summary>
+View the diff from {self.name} here.
+</summary>
+
+``````````diff
+{diff}
+``````````
+
+</details>
+"""
+
+    def find_comment(
+        self, pr: PullRequest.PullRequest
+    ) -> IssueComment.IssueComment | None:
+        for comment in pr.as_issue().get_comments():
+            if self.comment_tag in comment.body:
+                return comment
+        return None
+
+    def update_pr(self, diff: str, args: argparse.Namespace):
+        repo = github.Github(args.token).get_repo(args.repo)
+        pr = repo.get_issue(args.issue_number).as_pull_request()
+
+        existing_comment = self.find_comment(pr)
+        pr_text = self.pr_comment_text(diff)
+
+        if existing_comment:
+            existing_comment.edit(pr_text)
+        else:
+            pr.as_issue().create_comment(pr_text)
+
+    def update_pr_success(self, args: argparse.Namespace):
+        repo = github.Github(args.token).get_repo(args.repo)
+        pr = repo.get_issue(args.issue_number).as_pull_request()
+
+        existing_comment = self.find_comment(pr)
+        if existing_comment:
+            existing_comment.edit(
+                f"""
+{self.comment_tag}
+:white_check_mark: With the latest revision this PR passed the {self.friendly_name}.
+"""
+            )
+
+    def run(self, changed_files: [str], args: argparse.Namespace):
+        diff = self.format_run(changed_files, args)
+        if diff:
+            self.update_pr(diff, args)
+            return False
+        else:
+            self.update_pr_success(args)
+            return True
+
+
+class ClangFormatHelper(FormatHelper):
+    name = "clang-format"
+    friendly_name = "C/C++ code formatter"
+
+    @property
+    def instructions(self):
+        return " ".join(self.cf_cmd)
+
+    @cached_property
+    def libcxx_excluded_files(self):
+        with open("libcxx/utils/data/ignore_format.txt", "r") as ifd:
+            return [excl.strip() for excl in ifd.readlines()]
+
+    def should_be_excluded(self, path: str) -> bool:
+        for excl in self.libcxx_excluded_files:
+            if path == excl:
+                print(f"Excluding file {path}")
+                return True
+        return False
+
+    def filter_changed_files(self, changed_files: [str]) -> [str]:
+        filtered_files = []
+        for path in changed_files:
+            _, ext = os.path.splitext(path)
+            if ext in (".cpp", ".c", ".h", ".hpp", ".hxx", ".cxx"):
+                if not self.should_be_excluded(path):
+                    filtered_files.append(path)
+        return filtered_files
+
+    def format_run(self, changed_files: [str], args: argparse.Namespace) -> str | None:
+        self.args = args
+        cpp_files = self.filter_changed_files(changed_files)
+        if not cpp_files:
+            return
+        cf_cmd = [
+            "git-clang-format",
+            "--diff",
+            args.start_rev,
+            args.end_rev,
+            "--",
+        ] + cpp_files
+        print(f"Running: {' '.join(cf_cmd)}")
+        self.cf_cmd = cf_cmd
+        proc = subprocess.run(cf_cmd, capture_output=True)
+
+        # formatting needed
+        if proc.returncode == 1:
+            return proc.stdout.decode("utf-8")
+
+        return None
+
+
+class DarkerFormatHelper(FormatHelper):
+    name = "darker"
+    friendly_name = "Python code formatter"
+
+    @property
+    def instructions(self):
+        return " ".join(self.darker_cmd)
+
+    def filter_changed_files(self, changed_files: [str]) -> [str]:
+        filtered_files = []
+        for path in changed_files:
+            name, ext = os.path.splitext(path)
+            if ext == ".py":
+                filtered_files.append(path)
+
+        return filtered_files
+
+    def format_run(self, changed_files: [str], args: argparse.Namespace) -> str | None:
+        self.args = args
+        py_files = self.filter_changed_files(changed_files)
+        if not py_files:
+            return
+        darker_cmd = [
+            "darker",
+            "--check",
+            "--diff",
+            "-r",
+            f"{args.start_rev}..{args.end_rev}",
+        ] + py_files
+        print(f"Running: {' '.join(darker_cmd)}")
+        self.darker_cmd = darker_cmd
+        proc = subprocess.run(darker_cmd, capture_output=True)
+
+        # formatting needed
+        if proc.returncode == 1:
+            return proc.stdout.decode("utf-8")
+
+        return None
+
+
+ALL_FORMATTERS = (DarkerFormatHelper(), ClangFormatHelper())
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "--token", type=str, required=True, help="GitHub authentiation token"
+    )
+    parser.add_argument(
+        "--repo",
+        type=str,
+        default=os.getenv("GITHUB_REPOSITORY", "llvm/llvm-project"),
+        help="The GitHub repository that we are working with in the form of <owner>/<repo> (e.g. llvm/llvm-project)",
+    )
+    parser.add_argument("--issue-number", type=int, required=True)
+    parser.add_argument(
+        "--start-rev",
+        type=str,
+        required=True,
+        help="Compute changes from this revision.",
+    )
+    parser.add_argument(
+        "--end-rev", type=str, required=True, help="Compute changes to this revision"
+    )
+    parser.add_argument(
+        "--changed-files",
+        type=str,
+        help="Comma separated list of files that has been changed",
+    )
+
+    args = parser.parse_args()
+
+    changed_files = []
+    if args.changed_files:
+        changed_files = args.changed_files.split(",")
+
+    exit_code = 0
+    for fmt in ALL_FORMATTERS:
+        if not fmt.run(changed_files, args):
+            exit_code = 1
+
+    sys.exit(exit_code)

llvm/utils/git/requirements_formatting.txt

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+#
+# This file is autogenerated by pip-compile with Python 3.11
+# by the following command:
+#
+#    pip-compile --output-file=llvm/utils/git/requirements_formatting.txt llvm/utils/git/requirements_formatting.txt.in
+#
+black==23.9.1
+    # via
+    #   -r llvm/utils/git/requirements_formatting.txt.in
+    #   darker
+certifi==2023.7.22
+    # via requests
+cffi==1.15.1
+    # via
+    #   cryptography
+    #   pynacl
+charset-normalizer==3.2.0
+    # via requests
+click==8.1.7
+    # via black
+cryptography==41.0.3
+    # via pyjwt
+darker==1.7.2
+    # via -r llvm/utils/git/requirements_formatting.txt.in
+deprecated==1.2.14
+    # via pygithub
+idna==3.4
+    # via requests
+mypy-extensions==1.0.0
+    # via black
+packaging==23.1
+    # via black
+pathspec==0.11.2
+    # via black
+platformdirs==3.10.0
+    # via black
+pycparser==2.21
+    # via cffi
+pygithub==1.59.1
+    # via -r llvm/utils/git/requirements_formatting.txt.in
+pyjwt[crypto]==2.8.0
+    # via pygithub
+pynacl==1.5.0
+    # via pygithub
+requests==2.31.0
+    # via pygithub
+toml==0.10.2
+    # via darker
+urllib3==2.0.4
+    # via requests
+wrapt==1.15.0
+    # via deprecated

llvm/utils/git/requirements_formatting.txt.in

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+black~=23.0
+darker==1.7.2
+PyGithub==1.59.1