Add clang-tidy analysis of pull requests

This action runs clang-tidy with results saved to a file which is then
parsed in stage two to post code comments.  This multistage process lets
us post PR comments on code from forks.

Signed-off-by: Sean Robinson <sean.robinson@scottsdalecc.edu>

.github/workflows/tidy-analysis-stage-01.yml

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+# Insecure workflow with limited permissions that should provide analysis
+# results through an artifact.
+name: Tidy analysis
+
+on: pull_request
+
+jobs:
+
+  clang-tidy:
+
+    runs-on: ubuntu-20.04
+
+    steps:
+
+    - uses: actions/checkout@v3
+      with:
+        fetch-depth: 2
+
+    - name: Install clang-tidy
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y clang-tidy-12
+
+    - name: Prepare compile_commands.json
+      run: cmake -S . -B build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
+
+    - name: Create results directory
+      run: mkdir clang-tidy-result
+
+    - name: Analyze
+      run: git diff -U0 HEAD^ | clang-tidy-diff-12.py -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.ref }} > clang-tidy-result/pr-head-ref.txt
+
+    - uses: actions/upload-artifact@v2
+      with:
+        name: clang-tidy-result
+        path: clang-tidy-result/

.github/workflows/tidy-analysis-stage-02.yml

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+# Secure workflow with access to repository secrets and GitHub token
+# for posting analysis results.
+name: Post the Tidy analysis results
+
+on:
+  workflow_run:
+    workflows: [ "Tidy 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-20.04
+
+    steps:
+
+    - name: Download analysis results
+      uses: actions/github-script@v3.1.0
+      with:
+        script: |
+          let artifacts = await github.actions.listWorkflowRunArtifacts({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              run_id: ${{github.event.workflow_run.id }},
+          });
+          let matchArtifact = artifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "clang-tidy-result"
+          })[0];
+          let download = await github.actions.downloadArtifact({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              artifact_id: matchArtifact.id,
+              archive_format: "zip",
+          });
+          let fs = require("fs");
+          fs.writeFileSync("${{github.workspace}}/clang-tidy-result.zip", Buffer.from(download.data));
+
+    - name: Set environment variables
+      run: |
+        mkdir clang-tidy-result
+        unzip clang-tidy-result.zip -d clang-tidy-result
+        echo "pr_id=$(cat clang-tidy-result/pr-id.txt)" >> $GITHUB_ENV
+        echo "pr_head_repo=$(cat clang-tidy-result/pr-head-repo.txt)" >> $GITHUB_ENV
+        echo "pr_head_ref=$(cat clang-tidy-result/pr-head-ref.txt)" >> $GITHUB_ENV
+
+    - uses: actions/checkout@v3
+      with:
+        repository: ${{ env.pr_head_repo }}
+        ref: ${{ env.pr_head_ref }}
+        persist-credentials: false
+
+    - name: Redownload analysis results
+      uses: actions/github-script@v3.1.0
+      with:
+        script: |
+          let artifacts = await github.actions.listWorkflowRunArtifacts({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              run_id: ${{github.event.workflow_run.id }},
+          });
+          let matchArtifact = artifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "clang-tidy-result"
+          })[0];
+          let download = await github.actions.downloadArtifact({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              artifact_id: matchArtifact.id,
+              archive_format: "zip",
+          });
+          let fs = require("fs");
+          fs.writeFileSync("${{github.workspace}}/clang-tidy-result.zip", Buffer.from(download.data));
+
+    - name: Extract analysis results
+      run: |
+        mkdir clang-tidy-result
+        unzip clang-tidy-result.zip -d clang-tidy-result
+
+    - name: Run clang-tidy-pr-comments action
+      uses: platisd/clang-tidy-pr-comments@master
+      with:
+        github_token: ${{ secrets.GITHUB_TOKEN }}
+        clang_tidy_fixes: clang-tidy-result/fixes.yml
+        pull_request_id: ${{ env.pr_id }}