.github/workflows: Add PR formatting validator

This workflow runs when GitHub PRs are modified (edited, opened,
reopened, and synchronized) to perform basic validation of the PR
title and description.

Right now, this includes:

- Checking that PR template text does not remain in the PR description.
- Checking that the PR body is not empty.

If a check fails, a GitHub comment will be left on the PR and a
PR status check failure will be present on the PR until the issue
is resolved.

Signed-off-by: Michael Kubacki <[email protected]>

Author: makubacki

.github/workflows/pull-request-formatting-validator.yml

@@ -0,0 +1,83 @@
+# This workflow validates basic pull request formatting requirements are met.
+#
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+
+name: Validate Pull Request Formatting
+
+on:
+  pull_request_target:
+    types:
+      - edited
+      - opened
+      - reopened
+      - synchronize
+
+jobs:
+  validate_pr:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Generate Token
+        id: app-token
+        uses: actions/create-github-app-token@v2
+        with:
+          app-id: ${{ secrets.TIANOCORE_ASSIGN_REVIEWERS_APPLICATION_ID }}
+          private-key: ${{ secrets.TIANOCORE_ASSIGN_REVIEWERS_APPLICATION_PRIVATE_KEY }}
+
+      - run: |
+            prData="$(gh api graphql -F owner=$OWNER -F name=$REPO -F pr_number=$PR_NUMBER -f query='
+            query($name: String!, $owner: String!, $pr_number: Int!) {
+              repository(owner: $owner, name: $name) {
+              pullRequest(number: $pr_number) {
+                title
+                body
+              }
+              }
+            }')"
+
+            prTitle=$(echo "$prData" | jq -r '.data.repository.pullRequest.title')
+            prBody=$(echo "$prData" | jq -r '.data.repository.pullRequest.body')
+
+            templateContent="$(gh api repos/$OWNER/$REPO/contents/.github/pull_request_template.md --jq '.content' | base64 -d)"
+
+            # Template lines are those that begin with '<'
+            templateLines=$(echo "$templateContent" | grep '^<' || true)
+
+            if [[ -n "$templateLines" ]]; then
+              templateLinesFound=""
+              while IFS= read -r line; do
+              if [[ -n "$line" && "$prBody" == *"$line"* ]]; then
+                if [[ -n "$templateLinesFound" ]]; then
+                templateLinesFound="$templateLinesFound"$'\n'"\`$line\`"
+                else
+                templateLinesFound="\`$line\`"
+                fi
+              fi
+              done <<< "$templateLines"
+
+              if [[ -n "$templateLinesFound" ]]; then
+                gh pr comment $PR_URL --body "⚠️ Please remove the following template lines from your PR description:"$'\n'"$templateLinesFound"
+                echo 'VALIDATION_ERROR=true' >> $GITHUB_ENV
+              fi
+            fi
+
+            # Check if the PR body is empty
+            if [[ -z "$prBody" || "$prBody" == "null" ]]; then
+              gh pr comment $PR_URL --body "⚠️ Please add a pull request description."
+              echo 'VALIDATION_ERROR=true' >> $GITHUB_ENV
+            fi
+        env:
+          GITHUB_TOKEN: ${{ steps.app-token.outputs.token }}
+          OWNER: ${{ github.repository_owner }}
+          PR_NUMBER: ${{ github.event.number }}
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          REPO: ${{ github.event.repository.name }}
+
+      - name: Check for Validation Errors
+        if: env.VALIDATION_ERROR
+        uses: actions/github-script@v7
+        with:
+          script: |
+            core.setFailed('PR Formatting Validation Check Failed!')