chore: drop clang 11 support and update default version to 21

[shenxianpeng]

Summary

This PR drops support for clang version 11 and updates the default clang version from 20 to 21.

Changes

1. action.yml — Removed 11 from the list of accepted version strings and updated the default from '20' to '21'.
2. .github/workflows/self-test.yml — Removed '11' from the clang-version test matrix.

Motivation

Clang 11 is now several years old and is no longer actively maintained in the clang-tools-pip ecosystem. Clang 21 is the latest major version and should be the default going forward.

Summary by CodeRabbit

• Bug Fixes
  • Updated the supported toolchain version range to start at a newer minimum version.
  • Changed the default clang-tools version to a newer release.
  • The self-test workflow now runs against the updated version matrix, improving consistency with current supported versions.

[github-actions]

Cpp-Linter Report ⚠️

Some files did not pass the configured checks!

clang-format (v16.0.6) reports: 2 file(s) not formatted

• docs/examples/demo/demo.hpp
• docs/examples/demo/demo.cpp

clang-tidy (v16.0.6) reports: 7 concern(s)

• docs/examples/demo/demo.hpp:6:11: warning: [modernize-use-default-member-init]

  use default member initializer for 'useless'

      char* useless;
            ^
                   {"\0"}

• docs/examples/demo/demo.hpp:7:9: warning: [modernize-use-default-member-init]

  use default member initializer for 'numb'

      int numb;
          ^
              {0}

• docs/examples/demo/demo.hpp:11:11: warning: [modernize-use-trailing-return-type]

  use a trailing return type for this function

      void *not_useful(char *str){useless = str;}
      ~~~~~~^
      auto                        -> void *

• docs/examples/demo/demo.cpp:3:10: warning: [modernize-deprecated-headers]

  inclusion of deprecated C++ header 'stdio.h'; consider using 'cstdio' instead

  #include <stdio.h>
           ^~~~~~~~~
           <cstdio>

• docs/examples/demo/demo.cpp:8:5: warning: [modernize-use-trailing-return-type]

  use a trailing return type for this function

  int main(){
  ~~~ ^
  auto       -> int

• docs/examples/demo/demo.cpp:10:13: warning: [readability-braces-around-statements]

  statement should be inside braces

      for (;;) break;
              ^
               {

• docs/examples/demo/demo.cpp:13:5: warning: [cppcoreguidelines-pro-type-vararg]

  do not call c-style vararg functions

      printf("Hello world!\n");
      ^

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: e629c712-b883-45d1-bc5c-1f2d9db4d100

📥 Commits

Reviewing files that changed from the base of the PR and between 8e85cd0 and 5432019.

📒 Files selected for processing (2)

• .github/workflows/self-test.yml
• action.yml

---

Walkthrough

This PR updates supported Clang version references: the self-test workflow's clang-version matrix drops version 11 (starting at 12), and action.yml's version input documentation removes 11 from accepted options and changes the default from '20' to '21'.

Changes

Clang Version Support Update

Layer / File(s)	Summary
Update clang-version matrix and defaults .github/workflows/self-test.yml, action.yml	Self-test matrix drops clang-version 11 (starts at 12); action.yml documentation removes 11 from accepted options and updates default from '20' to '21'.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• cpp-linter/cpp-linter-action#299: Both PRs modify the clang-version self-test matrix and the version input options/default in action.yml.
• cpp-linter/cpp-linter-action#368: Both PRs touch action.yml's inputs.version definition affecting version handling logic.
• cpp-linter/cpp-linter-action#398: Both PRs modify the same clang-version enumerations in self-test.yml and action.yml's version input options/default.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: dropping clang 11 support and updating the default version to 21.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[shenxianpeng]

This PR will resolve the CI failure from #457 since the latest version of clang-tools and clang-tools-static-binaries drops support for clang version 11

[2bndy5]

Now that cpp-linter/clang-tools-static-binaries deploys a versions.json, the CI matrix could be automated

jobs:
  pre-seed-versions:
    runs-on: ubuntu-latest
    outputs:
      versions: ${{ steps.versions.outputs.versions }}
    steps:
      - id: versions
        env:
          # may not be needed because release assets are not rate limited
          GITHUB_TOKEN: ${{ github.token }}
        run: >-
          gh release download
          --repo cpp-linter/clang-tools-static-binaries
          --pattern "versions.json" -O -
          | python3 -c "import sys, json;
          d = json.load(sys.stdin);
          v = [x for x in d['llvm_versions']];
          print(f'versions={json.dumps(v)}')"
          >> $GITHUB_OUTPUT

  test:
    needs: [pre-seed-versions]
    permissions:
      contents: write
      pull-requests: write
    strategy:
      matrix:
        os: [ ubuntu-latest, macos-latest, windows-latest ]
        clang-version: ${{ fromJson(needs.pre-seed-versions.outputs.versions) }}

See fromJson() in GH docs.

Maybe the doc strings too, but that would be trickier

[shenxianpeng]

Good point. Since there are still other place that need to be updated, I think explicitly displaying the version range here seems reasonable.