chore: large PR checker (#274)

Implement the PR size checker we had in the previous repository, but
directly on a GitHub workflow.

Adapted from https://github.com/adolfosilva/gh-large-pr-check (MIT
License).

---
By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license

---------

Signed-off-by: github-actions <github-actions@github.com>
Co-authored-by: github-actions <github-actions@github.com>

Author: otaviomacedo

.gitattributes

@@ -9,6 +9,7 @@ import { CodeCovWorkflow } from './projenrc/codecov';
 import { ESLINT_RULES } from './projenrc/eslint';
 import { IssueLabeler } from './projenrc/issue-labeler';
 import { JsiiBuild } from './projenrc/jsii';
+import { LargePrChecker } from './projenrc/large-pr-checker';
 import { PrLabeler } from './projenrc/pr-labeler';
 import { RecordPublishingTimestamp } from './projenrc/record-publishing-timestamp';
 import { S3DocsPublishing } from './projenrc/s3-docs-publishing';
@@ -1515,4 +1516,8 @@ new CodeCovWorkflow(repo, {
 new IssueLabeler(repo);
 new PrLabeler(repo);
 
+new LargePrChecker(repo, {
+  excludeFiles: ['*.md', '*.test.ts', '*.yml'],
+});
+
 repo.synth();

.github/workflows/large-pr-checker.yml

@@ -0,0 +1,85 @@
+import { github, Component } from 'projen';
+import { JobPermission } from 'projen/lib/github/workflows-model';
+import type { TypeScriptProject } from 'projen/lib/typescript';
+
+export interface LargePrCheckerProps {
+  /**
+   * The number of lines changed in the PR that will trigger a comment and a failure.
+   *
+   * @default 1000
+   */
+  readonly maxLinesChanged?: number;
+
+  /**
+   * A list of files to exclude from the line count.
+   *
+   * @default - none
+   */
+  readonly excludeFiles?: string[];
+}
+
+export class LargePrChecker extends Component {
+  private readonly workflow: github.GithubWorkflow;
+
+  constructor(repo: TypeScriptProject, props: LargePrCheckerProps = {}) {
+    super(repo);
+
+    if (!repo.github) {
+      throw new Error('Given repository does not have a GitHub component');
+    }
+
+    const maxLinesChanged = props.maxLinesChanged ?? 1000;
+    const excludeFiles = (props.excludeFiles ?? [])
+      .map((pattern) => `':(exclude)${pattern}'`)
+      .join(' ');
+
+    this.workflow = repo.github.addWorkflow('large-pr-checker');
+    this.workflow.on({
+      pullRequest: {
+        branches: ['main'],
+        types: ['labeled', 'edited', 'opened', 'reopened', 'unlabeled'],
+      },
+    });
+
+    this.workflow.addJob('check', {
+      name: 'Check PR size',
+      if: '${{ !contains(github.event.pull_request.labels.*.name, \'pr/exempt-size-check\') }}',
+      runsOn: ['ubuntu-latest'],
+      permissions: {
+        pullRequests: JobPermission.WRITE,
+      },
+      steps: [
+        github.WorkflowSteps.checkout(),
+        {
+          id: 'fetch_target_branch',
+          run: 'git fetch origin main',
+        },
+        {
+          id: 'get_total_lines_changed',
+          run: `size=$(git diff --shortstat origin/main ${excludeFiles} \\
+        | awk '{ print $4+$6 }' \\
+        | awk -F- '{print $NF}' \\
+        | bc)
+        
+        echo "Total lines changed: $size"
+        echo "total_lines_changed=$size" >> $GITHUB_OUTPUT`,
+        },
+        {
+          id: 'comment_pr',
+          if: `$\{{ fromJSON(steps.get_total_lines_changed.outputs.total_lines_changed) > fromJSON(${maxLinesChanged}) }}`,
+          uses: 'thollander/actions-comment-pull-request@v2',
+          with: {
+            comment_tag: 'pr_size',
+            mode: 'recreate',
+            message: `Total lines changed $\{{ steps.get_total_lines_changed.outputs.total_lines_changed }} is greater than ${maxLinesChanged}. Please consider breaking this PR down.`,
+          },
+        },
+        {
+          id: 'fail',
+          if: `$\{{ fromJSON(steps.get_total_lines_changed.outputs.total_lines_changed) > fromJSON(${maxLinesChanged}) }}`,
+          run: 'exit 1',
+        },
+      ],
+    });
+  }
+}