Refactor PR Body regexing into independent GH Action

.github/actions/app-create/action.yml

@@ -26,46 +26,38 @@ outputs:
 runs:
   using: composite
   steps:
-    - name: Briefcase Template Override
-      id: template-override
-      env:
-        GITHUB_TOKEN: ${{ github.token }}
+    - name: Check for Briefcase Template Repo Override
+      id: template-repo-override
+      uses: ./beeware-.github/.github/actions/pr-body-parse
+      with:
+        key-regex: 'BRIEFCASE[-_]*TEMPLATE[-_]*REPO'
+        testing-pr-body: ${{ inputs.testing-pr-body }}
+
+    - name: Check for Briefcase Template Ref Override
+      id: template-ref-override
+      uses: ./beeware-.github/.github/actions/pr-body-parse
+      with:
+        key-regex: 'BRIEFCASE[-_]*TEMPLATE[-_]*REF'
+        testing-pr-body: ${{ inputs.testing-pr-body }}
+
+    - name: Declare Briefcase Template
+      id: template
       shell: bash
       run: |
-        # Check Body of PR for template to use
-        # (only PRs will have a value for github.event.pull_request.number)
-        PR_BODY="${{ inputs.testing-pr-body }}"
-        if [[ -z "${PR_BODY}" && -n "${{ github.event.pull_request.number }}" ]]; then
-          PR_BODY=$(gh api repos/${{ github.repository }}/pulls/${{ github.event.pull_request.number }} --jq '.body')
-        fi
-        printf "::group::Retrieved PR Body\n%s\n::endgroup::\n" "${PR_BODY}"
-
-        TEMPLATE_REPO=$(printf "%s" "${PR_BODY}" | perl -wlne '/BRIEFCASE[-_]*TEMPLATE[-_]*REPO:\s*\K\S+/i and print $&')
-        TEMPLATE_REF=$(printf "%s" "${PR_BODY}" | perl -wlne '/BRIEFCASE[-_]*TEMPLATE[-_]*REF:\s*\K\S+/i and print $&')
+        REPO="${{ steps.template-repo-override.outputs.extracted-value || inputs.briefcase-template-source }}"
+        REF="${{ steps.template-ref-override.outputs.extracted-value || inputs.briefcase-template-branch }}"
 
-        # If a template is not in the PR, use inputs specified in CI workflow
-        if [ -z "${TEMPLATE_REPO}" ]; then
-          TEMPLATE_REPO="${{ inputs.briefcase-template-source }}"
+        if [ -n "${REPO}" ]; then
+          echo "repo=$(printf -- "--template '%q'" "${REPO}")" | tee -a ${GITHUB_OUTPUT}
         fi
-        if [ -z "${TEMPLATE_REF}" ]; then
-          TEMPLATE_REF="${{ inputs.briefcase-template-branch }}"
+        if [ -n "${REF}" ]; then
+          echo "ref=$(printf -- "--template-branch '%q'" "${REF}")" | tee -a ${GITHUB_OUTPUT}
         fi
 
-        # Expose template repo and branch via outputs
-        echo "repo=${TEMPLATE_REPO}" | tee -a ${GITHUB_OUTPUT}
-        echo "ref=${TEMPLATE_REF}" | tee -a ${GITHUB_OUTPUT}
-
     - name: Create Briefcase Project
       id: create
       shell: bash
       run: |
-        if [[ "${{ steps.template-override.outputs.repo }}" != "" ]]; then
-          TEMPLATE=$(printf -- "--template %q" "${{ steps.template-override.outputs.repo }}")
-        fi
-        if [[ "${{ steps.template-override.outputs.ref }}" != "" ]]; then
-          TEMPLATE_BRANCH=$(printf -- "--template-branch %q" "${{ steps.template-override.outputs.ref }}")
-        fi
-
         # Map GUI toolkit through case insensitivity
         case "$(tr '[:upper:]' '[:lower:]' <<< "${{ inputs.framework }}")" in
           toga    ) BOOTSTRAP=Toga ;;
@@ -89,7 +81,7 @@ runs:
         rm -rf "${APP_DIR}"
 
         # Roll out the project
-        briefcase new --no-input ${TEMPLATE} ${TEMPLATE_BRANCH} \
+        briefcase new --no-input ${{ steps.template.outputs.repo }} ${{ steps.template.outputs.ref }} \
           -Q "formal_name=${APP_NAME}" \
           -Q "app_name=${APP_DIR}" \
           -Q "bootstrap=${BOOTSTRAP}"

.github/actions/pr-body-parse/action.yml

@@ -0,0 +1,37 @@
+name: PR Body Parse
+description: Parse a value from the body of the relevant PR for a specific key
+
+inputs:
+  key-regex:
+    description: "The regex for the key identifying the value to return, e.g. BRIEFCASE[-_]*REPO"
+    required: true
+  testing-pr-body:
+    description: "Override value for body of PR; only for testing."
+    required: false
+
+outputs:
+  extracted-value:
+    value: ${{ steps.parse.outputs.extracted-value }}
+    description: "The value extracted from the PR's body for the specified key."
+
+runs:
+  using: composite
+  steps:
+    - name: Parse PR Body for ${{ inputs.key-regex }}
+      id: parse
+      env:
+        GITHUB_TOKEN: ${{ github.token }}
+      shell: bash
+      run: |
+        # Retrieve PR Body (only PRs will have a value for github.event.pull_request.number)
+        PR_BODY="${{ inputs.testing-pr-body }}"
+        if [[ -z "${PR_BODY}" && -n "${{ github.event.pull_request.number }}" ]]; then
+          PR_BODY=$(gh api repos/${{ github.repository }}/pulls/${{ github.event.pull_request.number }} --jq '.body')
+        fi
+        printf "::group::Retrieved PR Body\n%s\n::endgroup::\n" "${PR_BODY}"
+
+        # Parse value with given regex
+        EXTRACTED_VALUE=$(printf "%s" "${PR_BODY}" | perl -wlne '/${{ inputs.key-regex }}:\s*\K\S+/i and print $&')
+
+        # Expose value as output
+        echo "extracted-value=${EXTRACTED_VALUE}" | tee -a ${GITHUB_OUTPUT}