github/workflows: Comment on code size change instead of failing CI.

This changes the code size workflow to post a comment on pull requests with
the code size report.  It also removes the error threshold so that the test
won't fail if code size increases.

Allowable code size changes are subjective, so shouldn't cause CI to fail.
In addition, failing CI tests can cause other hooks like code coverage
reports to be suppressed, so this fixes that problem as well.

Fixes issue #8464.

Signed-off-by: David Lechner <david@pybricks.com>

2 files changed, 79 insertions, 1 deletions

diff --git a/.github/workflows/code_size.yml b/.github/workflows/code_size.yml
index 3811d9134..d4f8b195a 100644
--- a/.github/workflows/code_size.yml
+++ b/.github/workflows/code_size.yml
@@ -24,4 +24,18 @@ jobs:
     - name: Build
       run: source tools/ci.sh && ci_code_size_build
     - name: Compute code size difference
-      run: tools/metrics.py diff --error-threshold 0 ~/size0 ~/size1
+      run: tools/metrics.py diff ~/size0 ~/size1 | tee > diff
+    - name: Save PR number
+      if: github.event_name == 'pull_request'
+      env:
+        PR_NUMBER: ${{ github.event.number }}
+      run: echo $PR_NUMBER > pr_number
+    - name: Upload diff
+      if: github.event_name == 'pull_request'
+      uses: actions/upload-artifact@v3
+      with:
+        name: code-size-report
+        path: |
+          diff
+          pr_number
+        retention-days: 1
diff --git a/.github/workflows/code_size_comment.yml b/.github/workflows/code_size_comment.yml
new file mode 100644
index 000000000..100e82f82
--- /dev/null
+++ b/.github/workflows/code_size_comment.yml
@@ -0,0 +1,64 @@
+name: Code size comment
+
+on:
+  workflow_run:
+    workflows: [Check code size]
+    types: [completed]
+
+jobs:
+  comment:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: 'Download artifact'
+        id: download-artifact
+        uses: actions/github-script@v6
+        with:
+          script: |
+            const fs = require('fs');
+
+            const allArtifacts = await github.rest.actions.listWorkflowRunArtifacts({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               run_id: context.payload.workflow_run.id,
+            });
+
+            const matchArtifact = allArtifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "code-size-report"
+            });
+
+            if (matchArtifact.length === 0) {
+              return false;
+            }
+
+            const download = await github.rest.actions.downloadArtifact({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               artifact_id: matchArtifact[0].id,
+               archive_format: 'zip',
+            });
+
+            fs.writeFileSync(`${process.env.GITHUB_WORKSPACE}/code-size-report.zip`, Buffer.from(download.data));
+
+            return true;
+      - name: 'Unzip artifact'
+        if: steps.download-artifact.outputs.result
+        run: unzip code-size-report.zip
+      - name: Post comment to pull request
+        if: steps.download-artifact.outputs.result
+        uses: actions/github-script@v6
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            const fs = require('fs');
+
+            github.rest.issues.createComment({
+              issue_number: Number(fs.readFileSync('pr_number')),
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: `Code size report:
+
+            \`\`\`
+            ${fs.readFileSync('diff')}
+            \`\`\`
+            `,
+            });