Merge pull request #309 from AArnott/workflowfixes

Workaround github's protections for workflow changes in GitHub Actions

.github/workflows/libtemplate-update.yml

@@ -43,7 +43,26 @@ jobs:
           exit 0
         }
 
-        git -c http.extraheader="AUTHORIZATION: bearer $env:GH_TOKEN" push origin -u FETCH_HEAD:refs/heads/auto/libtemplateUpdate
+        # Pushing commits that add or change files under .github/workflows will cause our workflow to fail.
+        # But it usually isn't necessary because the target branch already has (or doesn't have) these changes.
+        # So if the merged doesn't bring in any changes to these files, try the merge locally and push that
+        # to keep github happy.
+        if ((git rev-list FETCH_HEAD ^HEAD --count -- .github/workflows) -eq 0) {
+          # Indeed there are no changes in that area. So merge locally to try to appease GitHub.
+          git checkout -b auto/libtemplateUpdate
+          git config user.name "Andrew Arnott"
+          git config user.email "[email protected]"
+          git merge FETCH_HEAD
+          if ($LASTEXITCODE -ne 0) {
+            Write-Host "Merge conflicts prevent creating the pull request. Please run tools/MergeFrom-Template.ps1 locally and push the result as a pull request."
+            exit 2
+          }
+
+          git -c http.extraheader="AUTHORIZATION: bearer $env:GH_TOKEN" push origin -u HEAD
+        } else {
+          Write-Host "Changes to github workflows are included in this update. Please run tools/MergeFrom-Template.ps1 locally and push the result as a pull request."
+          exit 1
+        }
     - name: pull request
       shell: pwsh
       if: success() && steps.merge.outputs.uptodate != 'true'
@@ -58,6 +77,8 @@ jobs:
         $prTitle = "Merge latest Library.Template"
         $prBody = "This merges the latest features and fixes from [Library.Template's  branch](https://github.com/AArnott/Library.Template/tree/).
 
+        ⚠️ Do **not** squash this pull request when completing it. You must *merge* it."
+
         <details>
         <summary>Merge conflicts?</summary>
         Resolve merge conflicts locally by carrying out these steps:
@@ -72,8 +93,6 @@ jobs:
         ```
         </details>
 
-        ⚠️ Do **not** squash this pull request when completing it. You must *merge* it."
-
         gh pr create -H auto/libtemplateUpdate -b $prBody -t $prTitle
       env:
         GH_TOKEN: ${{ github.token }}