Add workflows for publishing via GH pages

This change adds a Github workflow that builds the website and
publishes the build result to branch `gh-pages` for every commit
on `master`. In addition, it deploys a preview to
https://github.com/eclipse-theia/theia-website-previews.

Effectively, this is the first step of changing the hosting of the
Theia website from Netlify to Github pages.

For more information see
https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/3874

This change applies the same technique as used in
https://github.com/eclipse-langium/langium-website

Co-authored-by: Olaf Lessenich <[email protected]>

.github/workflows/preview.yml

@@ -0,0 +1,87 @@
+name: Deploy PR previews
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - closed
+
+concurrency: preview-${{ github.head_ref }}
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  build-preview:
+    if: github.event_name == 'pull_request_target' && github.event.action != 'closed'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Use Node.js 14.x
+        uses: actions/setup-node@1a4442cacd436585916779262731d5b162bc6ec7 #v3
+        with:
+          node-version: '14.x'
+          registry-url: 'https://registry.npmjs.org'
+      - name: Checkout
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 #v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Build website
+        run: |
+          npm install
+          PATH_PREFIX="pr-previews/${{ github.event.number }}" npm run build -- --prefix-paths
+      - name: Upload artifact
+        uses: actions/upload-artifact@5d5d22a31266ced268874388b861e4b58bb5c2f3 #v4
+        with:
+          name: "site"
+          path: ./public
+
+  deploy-preview:
+    needs: build-preview
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    environment:
+      name: pull-request-preview
+      url: ${{ steps.deployment.outputs.deployment-url }}
+    steps:
+      # checkout required for pr-preview-action to succeed,
+      # while the content will not be used
+      - name: Checkout
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 #v4
+      - name: Download the preview page
+        uses: actions/download-artifact@c850b930e6ba138125429b7e5c93fc707a7f8427 #v4
+        with:
+          name: "site"
+          path: ./public
+      - uses: rossjrw/pr-preview-action@f31d5aa7b364955ea86228b9dcd346dc3f29c408 #v1
+        id: deployment
+        with:
+          source-dir: ./public
+          preview-branch: previews
+          umbrella-dir: pr-previews
+          deploy-repository: eclipse-theia/theia-website-previews
+          token: ${{ secrets.DEPLOY_PREVIEW_TOKEN }}
+          action: auto
+
+  # remove the preview page when the PR got closed
+  remove-preview:
+    if: github.event_name == 'pull_request_target' && github.event.action == 'closed'
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      # checkout required for pr-preview-action to succeed,
+      # while the content will not be used
+      - name: Checkout
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 #v4
+      - uses: rossjrw/pr-preview-action@f31d5aa7b364955ea86228b9dcd346dc3f29c408 #v1
+        id: deployment
+        with:
+          preview-branch: previews
+          umbrella-dir: pr-previews
+          deploy-repository: eclipse-theia/theia-website-previews
+          token: ${{ secrets.DEPLOY_PREVIEW_TOKEN }}
+          action: auto

.github/workflows/publish.yml

@@ -0,0 +1,46 @@
+name: Deploy Website
+
+on:
+  push:
+    branches: ["master"]
+  workflow_dispatch:
+
+# Allow only one concurrent deployment
+# Do not cancel in progress as we want production deployments to complete.
+concurrency:
+  group: "publish"
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout website sources
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 #v4
+      - name: Use Node.js 14.x
+        uses: actions/setup-node@1a4442cacd436585916779262731d5b162bc6ec7 #v3
+        with:
+          node-version: 14.x
+          registry-url: 'https://registry.npmjs.org'
+      - name: Configure Pages
+        id: pages
+        uses: actions/configure-pages@1f0c5cde4bc74cd7e1254d0cb4de8d49e9068c7d #v4
+      - name: Build website
+        run: |
+          npm install
+          npm run build
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@56afc609e74202658d3ffba0e8f6dda462b719fa #v3
+        with:
+          path: ./public
+
+  publish:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e #v4

README.md

@@ -28,6 +28,11 @@ npm run serve
 ## CI
 
 The website is automatically built at and deployed to Netlify.
+A preview of each PR is deployed to Netlify.
+
+In addition, every commit on `master` is built and published to branch `gh-pages`, which will soon replace the deployment of Netlify.
+A preview of every pull request is published at [eclipse-theia/theia-website-previews](https://github.com/eclipse-theia/theia-website-previews).
+For more information, see [`publish.yml`](.github/workflows/publish.yml) and [`preview.yml`](.github/workflows/preview.yml).
 
 ## License
 

gatsby-config.js

@@ -1,4 +1,5 @@
 module.exports = {
+    pathPrefix: process.env.PATH_PREFIX,
     siteMetadata: {
         title: 'Theia - Cloud and Desktop IDE Platform',
         description: "Theia is an open-source cloud   desktop IDE framework implemented in TypeScript."