feat: add go mod tidy check

README.md

@@ -346,3 +346,29 @@ include:
     ref: v1.11.0 # renovate:managed
     file: go-unittests.yml
 ```
+
+
+### [`go-mod-tidy`](./go-mod-tidy.yml)
+
+Ensures that [`go mod tidy`](https://go.dev/ref/mod) is up-to-date and `go.mod` and `go.sum` are tidy.
+
+1. Ensure that the `GL_ASDF_GOLANG_VERSION` version for Go is configured.
+
+```yaml
+stages:
+  - validate
+
+# Not needed if .gitlab-ci-asdf-versions.yml is included...
+variables:
+  GL_ASDF_GOLANG_VERSION: ...
+
+include:
+  # Not required, but recommended
+  - local: .gitlab-ci-asdf-versions.yml
+
+  # Perform `go mod tidy` and ensure that go.mod and go.sum are tidy.
+  # see https://gitlab.com/gitlab-com/gl-infra/common-ci-tasks/-/blob/main/README.md#go-mod-tidy
+  - project: 'gitlab-com/gl-infra/common-ci-tasks'
+    ref: v1.12.0 # renovate:managed
+    file: go-mod-tidy.yml
+```

go-mod-tidy.yml

+go_mod_tidy:
+  image: golang:${GL_ASDF_GOLANG_VERSION}
+  stage: validate
+  needs: []
+  script:
+    - go mod tidy
+    - git diff --exit-code || {
+        echo "running 'go mod tidy' produced changes.";
+        echo "please run 'go mod tidy' and commit the changes.";
+        exit 1;
+      }
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH