ci: Add clang-tidy comments for PR's

There are two seperate actions: One for running clang-tidy with no
secrets, and another with secrets. This ensures that if the former is
compromised, the latter secrets should be safe.

Signed-off-by: Urmas Rist <urmas@leil.io>

Author: uristdwarf

.github/workflows/post-static-analysis.yml

@@ -0,0 +1,93 @@
+# Secure workflow with access to repository secrets and GitHub token for posting analysis results
+name: Post the static analysis results
+
+on:
+  workflow_run:
+    workflows: [ "Static analysis" ]
+    types: [ completed ]
+
+jobs:
+  clang-tidy-results:
+    # Trigger the job only if the previous (insecure) workflow completed successfully
+    if: ${{ github.event.workflow_run.event == 'pull_request' && github.event.workflow_run.conclusion == 'success' }}
+    runs-on: ubuntu-22.04
+    permissions:
+      pull-requests: write
+      # OPTIONAL: auto-closing conversations requires the `contents` permission
+      contents: write
+    steps:
+    - name: Download analysis results
+      uses: actions/github-script@v7
+      with:
+        script: |
+          const artifacts = await github.rest.actions.listWorkflowRunArtifacts({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              run_id: ${{ github.event.workflow_run.id }},
+          });
+          const matchArtifact = artifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "clang-tidy-result"
+          })[0];
+          const download = await github.rest.actions.downloadArtifact({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              artifact_id: matchArtifact.id,
+              archive_format: "zip",
+          });
+          const fs = require("fs");
+          fs.writeFileSync("${{ github.workspace }}/clang-tidy-result.zip", Buffer.from(download.data));
+    - name: Extract analysis results
+      run: |
+        mkdir clang-tidy-result
+        unzip -j clang-tidy-result.zip -d clang-tidy-result
+    - name: Set environment variables
+      uses: actions/github-script@v7
+      with:
+        script: |
+          const assert = require("node:assert").strict;
+          const fs = require("fs");
+          function exportVar(varName, fileName, regEx) {
+              const val = fs.readFileSync("${{ github.workspace }}/clang-tidy-result/" + fileName, {
+                  encoding: "ascii"
+              }).trimEnd();
+              assert.ok(regEx.test(val), "Invalid value format for " + varName);
+              core.exportVariable(varName, val);
+          }
+          exportVar("PR_ID", "pr-id.txt", /^[0-9]+$/);
+          exportVar("PR_HEAD_REPO", "pr-head-repo.txt", /^[-./0-9A-Z_a-z]+$/);
+          exportVar("PR_HEAD_SHA", "pr-head-sha.txt", /^[0-9A-Fa-f]+$/);
+    - uses: actions/checkout@v4
+      with:
+        repository: ${{ env.PR_HEAD_REPO }}
+        ref: ${{ env.PR_HEAD_SHA }}
+        persist-credentials: false
+    - name: Redownload analysis results
+      uses: actions/github-script@v7
+      with:
+        script: |
+          const artifacts = await github.rest.actions.listWorkflowRunArtifacts({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              run_id: ${{ github.event.workflow_run.id }},
+          });
+          const matchArtifact = artifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "clang-tidy-result"
+          })[0];
+          const download = await github.rest.actions.downloadArtifact({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              artifact_id: matchArtifact.id,
+              archive_format: "zip",
+          });
+          const fs = require("fs");
+          fs.writeFileSync("${{ github.workspace }}/clang-tidy-result.zip", Buffer.from(download.data));
+    - name: Extract analysis results
+      run: |
+        mkdir clang-tidy-result
+        unzip -j clang-tidy-result.zip -d clang-tidy-result
+    - name: Run clang-tidy-pr-comments action
+      uses: platisd/clang-tidy-pr-comments@v1
+      with:
+        github_token: ${{ secrets.GITHUB_TOKEN }}
+        clang_tidy_fixes: clang-tidy-result/fixes.yml
+        pull_request_id: ${{ env.PR_ID }}

.github/workflows/static-analysis.yml

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+# Insecure workflow with limited permissions that should provide analysis results through an artifact
+name: Static analysis
+
+on: pull_request
+
+jobs:
+  clang-tidy:
+    runs-on: ubuntu-22.04
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        ref: ${{ github.event.pull_request.head.sha }}
+        fetch-depth: 0
+    - name: Fetch base branch
+      run: |
+        git remote add upstream "https://github.com/${{ github.event.pull_request.base.repo.full_name }}"
+        git fetch --no-tags --no-recurse-submodules upstream "${{ github.event.pull_request.base.ref }}"
+    - name: Install clang-tidy
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y clang-tidy
+    - name: Prepare compile_commands.json
+      run: |
+        cmake -B build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
+    - name: Create results directory
+      run: |
+        mkdir clang-tidy-result
+    - name: Analyze
+      run: |
+        git diff -U0 "$(git merge-base HEAD "upstream/${{ github.event.pull_request.base.ref }}")" | clang-tidy-diff -p1 -path build -export-fixes clang-tidy-result/fixes.yml
+    - name: Save PR metadata
+      run: |
+        echo "${{ github.event.number }}" > clang-tidy-result/pr-id.txt
+        echo "${{ github.event.pull_request.head.repo.full_name }}" > clang-tidy-result/pr-head-repo.txt
+        echo "${{ github.event.pull_request.head.sha }}" > clang-tidy-result/pr-head-sha.txt
+    - uses: actions/upload-artifact@v4
+      with:
+        name: clang-tidy-result
+        path: clang-tidy-result/