CI: only build without lockfile if dependencies changed (#2643)

* CI: build without lockfile if dependencies changed

- Makes this job less noisy if dependencies weren't modified.
- Comment on the PR in case of failure to communicate that PR can still
  be merged.
- Add badge to readme to make failures on main or scheduled builds
  visible.

* CI: enable path gating

Author: sveitser

.github/workflows/build-without-lockfile.yml

@@ -11,6 +11,10 @@ on:
   schedule:
     - cron: "0 0 * * 1"
   pull_request:
+    # Only run on PRs if dependencies were modified.
+    paths:
+      - "**/Cargo.toml"
+      - "**/Cargo.lock"
   workflow_dispatch:
 
 concurrency:
@@ -33,3 +37,52 @@ jobs:
         run: |
           cargo generate-lockfile
           cargo check --all-targets
+
+      - name: Comment on PR
+        uses: actions/github-script@v7
+        if: failure() && github.event_name == 'pull_request'
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            const issue_number = context.issue.number;
+            const owner = context.repo.owner;
+            const repo = context.repo.repo;
+            const runUrl = `https://github.com/${process.env.GITHUB_REPOSITORY}/actions/runs/${process.env.GITHUB_RUN_ID}`;
+
+            const commentTitle = "Unable to build without Cargo.lock file"
+            const commentBody = `${commentTitle}.
+
+            This means that after this change 3rd party projects may have
+            difficulties using crates in this repo as a dependency. If this
+            isn't easy to fix please open an issue so we can fix it later.
+
+            For the first failing build see: ${runUrl}
+
+            To reproduce locally run
+
+            \`\`\`
+            cargo generate-lockfile
+            cargo check --all-targets
+            \`\`\`
+
+            This PR can still be merged.`;
+
+            // Fetch existing comments
+            const { data: comments } = await github.rest.issues.listComments({
+              owner,
+              repo,
+              issue_number,
+            });
+
+            // Find existing comment
+            const existingComment = comments.find(c => c.body.startsWith(commentTitle));
+            if (!existingComment) {
+              await github.rest.issues.createComment({
+                owner,
+                repo,
+                issue_number,
+                body: commentBody
+              });
+            } else {
+              console.log("Already commented.")
+            }

README.md

@@ -7,6 +7,7 @@
 [![Lint](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/lint.yml/badge.svg)](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/lint.yml)
 [![Audit](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/audit.yml/badge.svg)](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/audit.yml)
 [![Ubuntu](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/ubuntu-install-without-nix.yml/badge.svg)](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/ubuntu-install-without-nix.yml)
+[![Build without lockfile](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/build-without-lockfile.yml/badge.svg)](https://github.com/EspressoSystems/espresso-sequencer/actions/workflows/build-without-lockfile.yml)
 [![Coverage Status](https://coveralls.io/repos/github/EspressoSystems/espresso-sequencer/badge.svg?branch=main)](https://coveralls.io/github/EspressoSystems/espresso-sequencer?branch=main)
 
 The Espresso Sequencer offers rollups credible neutrality and enhanced interoperability, without compromising on scale.