Setup PR Comment Workflow

Author: Benjamin-Philip

.github/workflows/pr_comment.yml

@@ -0,0 +1,53 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+name: PR comment
+
+on:
+  pull_request_target:
+    types:
+      - opened
+
+permissions:
+  contents: read
+  issues: write
+  pull-requests: write
+
+jobs:
+  preview-url:
+    name: Preview URL
+    runs-on: ubuntu-latest
+    steps:
+      - name: Comment
+        env:
+          GH_TOKEN: ${{ github.token }}
+          PR_REPOSITORY: ${{ github.event.pull_request.base.repo.full_name }}
+          FORK_REPOSITORY: ${{ github.event.pull_request.head.repo.full_name }}
+          PR_NUMBER: ${{ github.event.number }}
+        run: |
+          configure_url="https://github.com/apache/arrow-erlang/blob/main/CONTRIBUTING.md#forks"
+          fork_owner=${FORK_REPOSITORY%/*}
+          fork_repository=${FORK_REPOSITORY#*/}
+          {
+            echo "Preview URL: https://${fork_owner}.github.io/${fork_repository}"
+            echo ""
+            echo "If the preview URL doesn't work, you may forget to configure your fork repository for preview."
+            echo "See ${configure_url} how to configure."
+          } | tee body.md
+          gh pr comment ${PR_NUMBER} \
+            --body-file body.md \
+            --repo ${PR_REPOSITORY}

CONTRIBUTING.md

@@ -120,3 +120,38 @@ Please read our [development
 documentation](https://arrow.apache.org/docs/developers/index.html) or
 look through the [New Contributor's
 Guide](https://arrow.apache.org/docs/developers/guide/index.html).
+
+### Forks
+
+We deploy a preview of the ExDoc documentation of any fork as a part of our
+tests.
+
+On a commit to all branches, the rendered static site will be
+published to GitHub Pages using GitHub Actions. The latest commit is
+only visible because all publications use the same url:
+https://${YOUR_GITHUB_ACCOUNT}.github.io/arrow-erlang/
+
+You need to configure your fork repository to use this feature:
+
+1. Enable GitHub Pages on your fork:
+   1. Open https://github.com/${YOUR_GITHUB_ACCOUNT}/arrow-erlang/settings/pages
+   2. Select "GitHub Actions" as "Source"
+2. Accept publishing GitHub Pages from all branches on your fork:
+   1. Open https://github.com/${YOUR_GITHUB_ACCOUNT}/arrow-erlang/settings/environments
+   2. Select the "github-pages" environment
+   3. Change the default "Deployment branches and tags" rule:
+      1. Press the "Edit" button
+      2. Change the "Name pattern" to `*` from `main` or `gh-pages`
+
+See also the [GitHub Pages
+documentation](https://docs.github.com/en/pages/getting-started-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site#publishing-with-a-custom-github-actions-workflow).
+
+
+FYI: You can also generate the site for https://arrow.apache.org/arrow-erlang/main
+to `doc/` locally by running the following:
+
+
+```shell
+rebar3 ex_doc
+```
+