ci: Skip the smoke test on branches which only change files it does not read

.buildkite/pipeline.yaml

@@ -12,10 +12,43 @@ steps:
     command: .buildkite/prettier-check.sh
     agents: { queue: "vagrant" }
 
-  - label: ":rice: docker-compose-test"
+  # Builds on main always run the smoke test. if_changed compares against origin/main,
+  # so it finds no changes in a commit which is already on main, unless it is the newest
+  - &smoke_test
+    label: ":rice: docker-compose-test"
     command: .buildkite/vagrant-run.sh docker-test
     artifact_paths: ./*.log
     agents: { queue: "vagrant" }
+    if: build.branch == "main"
+
+  # Builds on other branches skip the smoke test if they only change files it does not read.
+  # New files run it, until someone adds them here
+  - <<: *smoke_test
+    if: build.branch != "main"
+    if_changed:
+      include: "**"
+      exclude:
+        # Docs, including the PR template and READMEs in mounted directories
+        - "**.md"
+        # GitHub Actions, editor and repository settings
+        - ".github/**"
+        - ".vscode/**"
+        - ".gitignore"
+        - "renovate.json"
+        # Release manifests
+        - "release.yaml"
+        - "batch-change/**"
+        # Prettier inputs, which the :lipstick: step checks
+        - ".prettierignore"
+        - "prettier.config.js"
+        - "package.json"
+        - "package-lock.json"
+        # Compose files the smoke test does not start
+        - "docker-compose/db-only-migrate.docker-compose.yaml"
+        - "docker-compose/dev/**"
+        - "docker-compose/examples/**"
+        # Caddyfiles the base file leaves commented out
+        - "caddy/builtins/https.*"
 
   # Please keep in mind that the release manifest uses specific branch names when creating releases.
   # Therefore, if you update them, or if you decide to change how we detect what kind of build we're dealing

AGENTS.md

@@ -24,6 +24,7 @@ CI runs these on every branch. `.tool-versions` pins Node and the GitHub CLI; CI
 
 - `test/smoke-test.sh` starts the base file, and compares the number of running containers with `expect_containers`. Update that number in the same pull request that adds or removes a service.
 - CI does not run `test/executor-smoke-test.sh`. Run it against a running deployment when you change `docker-compose/executors/`.
+- A branch which only changes files listed in the step's `if_changed` `exclude` skips the step. Builds on `main` always run it. When the smoke test starts reading a file on that list, remove it from the list.
 - The VM image is built from `gcp/images/e2e` in sourcegraph/infrastructure.
 
 ## Conventions