Create check-depgraph.yml (#509)

# Objective

- When the project structure changes, the dependency graph in
`assets/depgraph.svg` needs to be updated. However, there's nothing in
place to enforce this.

# Solution

- Add a GitHub workflow to check this. It automatically leaves a comment
on the pull request containing the new file.

.github/workflows/check-depgraph.yml

@@ -0,0 +1,65 @@
+name: Check Depgraph
+
+on:
+ pull_request:
+ branches: [ "main" ]
+
+env:
+ CARGO_TERM_COLOR: always
+
+permissions:
+ # Needed in order to leave comments on pull requests.
+ pull-requests: 'write'
+
+jobs:
+ check-depgraph:
+ runs-on: ubuntu-latest
+ steps:
+ - name: Checkout Actions Repository
+ uses: actions/checkout@v3
+
+ - name: Install cargo-depgraph
+ uses: baptiste0928/[email protected]
+ with:
+ crate: cargo-depgraph
+
+ - name: Install graphviz
+ run: sudo apt update && sudo apt install -y graphviz
+
+ - name: Generate new depgraph
+ run: cargo depgraph --workspace-only | tred | dot -Tsvg -o assets/depgraph.svg
+
+ - name: Check depgraph diff
+ run: git diff --exit-code assets/depgraph.svg > assets/depgraph.patch
+
+ - name: Create comment file
+ if: ${{ failure() }}
+ run: |
+ echo "It looks like this pull request changed the workspace structure. \
+ Please replace \`assets/depgraph.svg\` with the following text:
+ 
+ <details>
+ <summary>depgraph.svg (Don't forget the trailing newline)</summary>
+ 
+ \`\`\`html
+ $(cat assets/depgraph.svg)
+
+ \`\`\`
+ </details>
+ 
+ For reference, here is a diff against the old \`depgraph.svg\`:
+
+ <details>
+
+ \`\`\`patch
+ $(cat assets/depgraph.patch)
+ \`\`\`
+ </details>" >> pr-comment.txt
+
+ - name: Create pull request comment
+ uses: marocchino/sticky-pull-request-comment@v2
+ if: ${{ failure() }}
+ with:
+ recreate: true
+ header: depgraph
+ path: pr-comment.txt