add source link commit override

.github/workflows/README.md

@@ -48,7 +48,10 @@ uploaded anywhere.
   - `RRD_ARTIFACT_NAME` - Intermediate name of the GitHub rrd artifact. This should match the name passed to
     `reusable_build_and_test_wheels.yml`
   - `UPLOAD_COMMIT_OVERRIDE` - If set, will replace the value of `<commit>`. This is necessary because we want pull
+  request builds associated with their originating commit, even if the web-build happens on an ephemeral merge-commit.
 - [reusable_build_web_demo.yml](reusable_build_web.yml) - This job builds the assets uploaded to `demo.rerun.io`.
+  - `SOURCE_LINK_COMMIT_OVERRIDE` - If set, will replace the value of `<commit>` in the built app. This ensures that the
+  source source code link in the built app always points to the pull request's `HEAD`.
 - [reusable_upload_web_demo.yml](reusable_upload_web_demo.yml) - This job uploads the `demo.rerun.io` assets to google cloud. By default this
   only uploads to: `demo.rerun.io/commit/<commit>/`
   - `MARK_PRERELEASE_FOR_MAINLINE` - If true, then the web assets will go to `demo.rerun.io/prelease/

.github/workflows/on_pull_request.yml

@@ -51,6 +51,7 @@ jobs:
     with:
       CONCURRENCY: pr-${{ github.event.pull_request.number }}
       WHEEL_ARTIFACT_NAME: linux-wheel-fast
+      SOURCE_LINK_COMMIT_OVERRIDE: ${{ github.event.pull_request.head.sha }}
     secrets: inherit
 
   upload-web-demo:

.github/workflows/reusable_build_web_demo.yml

@@ -9,6 +9,12 @@ on:
       WHEEL_ARTIFACT_NAME:
         required: true
         type: string
+      # Each example in the built app contains a link to its source code.
+      # This determines the target commit to link to, and by default
+      # it is the current commit (github.sha)
+      SOURCE_LINK_COMMIT_OVERRIDE:
+        required: false
+        type: string
 
 concurrency:
   group: ${{ inputs.CONCURRENCY }}-build-web-demo
@@ -70,9 +76,18 @@ jobs:
           which rerun
           rerun --version
 
+      - name: Resolve source link commit hash
+        run: |
+          if [ -z "${{ inputs.SOURCE_LINK_COMMIT_OVERRIDE }}" ]; then
+            USED_SHA=${{ github.sha }}
+          else
+            USED_SHA=${{ inputs.SOURCE_LINK_COMMIT_OVERRIDE }}
+          fi
+          echo "SHORT_SHA=$(echo $USED_SHA | cut -c1-7)" >> $GITHUB_ENV
+
       - name: Build web demo
         env:
-          COMMIT_HASH: ${{ github.env.GITHUB_SHA }}
+          COMMIT_HASH: ${{ env.SHORT_SHA }}
         run: |
           python3 scripts/build_demo_app.py --skip-wasm-build