Add support for external repositories with pull request previews

.github/actions/build/action.yml

@@ -0,0 +1,34 @@
+name: Build
+description: Builds a project instance, assuming all the correct project files are in the build folder
+
+inputs:
+    base:
+        name: Base path
+        description: The path to use as a base for linking
+        required: true
+        default: /
+    folder:
+        name: Build Folder
+        description: The folder to try to build from
+        required: true
+        default: .
+
+runs:
+    using: composite
+    steps:
+        - name: Setup Node
+          uses: actions/setup-node@v2
+          with:
+              node-version: 15
+              cache: "yarn"
+
+        - run: yarn install
+        # - run: yarn check
+
+        - name: build
+          env:
+              BUILD_FOLDER: ${{ inputs.folder }}
+              BASE: ${{ inputs.base }}
+          run: |
+              cd "$BUILD_FOLDER"
+              yarn build --base "$BASE"

.github/workflows/preview_cleanup.yml

@@ -1,8 +1,8 @@
 name: Clean Preview
 
 #! Safety:
-#! this workflow should not execute any code at all
+#! this workflow should not execute any untrusted input at all
-#! see githubs docs on pull_request_target for more
+#! see the docs on `pull_request_target` for more
 on:
     pull_request_target:
         types: [unlabeled]

.github/workflows/preview_pull_request.yml

@@ -1,40 +1,43 @@
 name: Preview Pull Request
 
+#! Safety:
+#! this workflow should not execute any untrusted input at all
+#! see the docs on `pull_request_target` for more
 on:
-    pull_request:
+    pull_request_target:
         types: [synchronize, reopened, labeled]
 
 jobs:
-    build:
+    preview:
         runs-on: ubuntu-latest
         # make sure the pull request is labeled with 'use-preview'
         if: github.event.label.name == 'use-preview' || contains(github.event.pull_request.labels.*.name, 'use-preview')
+        env:
+            BASE: refs/pull/${{ github.event.pull_request.number }}/merge
+            REPO: ${{ github.event.repository.name }}
 
         steps:
+            - uses: actions/checkout@v2
+
             - uses: actions/checkout@v2
               with:
                   # Head commit of the pull request
                   ref: ${{ github.event.pull_request.head.sha }}
+                  path: pull
                   submodules: recursive
 
-            - name: Setup Node
-              uses: actions/setup-node@v2
-              with:
-                  node-version: 15
-                  cache: "yarn"
-
-            - run: yarn install
-            # - run: yarn check
-
             - name: build
-              run: yarn build --base "/revite/${{ github.ref }}/"
+              uses: ./.github/actions/build_preview
+              with:
+                  base: /${{ env.REPO }}/${{ env.BASE }}/
+                  folder: pull
 
             - name: publish preview
               uses: JamesIves/github-pages-deploy-action@4.1.5
               with:
                   folder: dist
                   branch: build-previews
-                  target-folder: ${{ github.ref }}
+                  target-folder: ${{ env.BASE }}
                   single-commit: true
 
             - name: send comment
@@ -43,6 +46,6 @@ jobs:
                   header: Preview environment
                   message: |
                       ## Preview environment
-                      https://${{ github.repository_owner }}.github.io/revite/${{ github.ref }}/
+                      https://${{ github.repository_owner }}.github.io/${{ env.REPO }}/${{ env.BASE }}/
 
                       This link will remain active until the `use-preview` label is removed.