Add npm.latest.gitlab-ci.yml to only run `publish` if necessary

lib/gitlab/ci/templates/npm.latest.gitlab-ci.yml

+publish:
+  image: node:latest
+  stage: deploy
+  rules:
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH || $CI_COMMIT_REF_NAME =~ /^v\d+\.\d+\.\d+.*$/
+      changes:
+        - package.json
+  script:
+    # If no .npmrc if included in the repo, generate a temporary one that is configured to publish to GitLab's NPM registry
+    - |
+      if [[ ! -f .npmrc ]]; then
+        echo 'No .npmrc found! Creating one now. Please review the following link for more information: https://docs.gitlab.com/ee/user/packages/npm_registry/index.html#project-level-npm-endpoint-1'
+        {
+          echo "@${CI_PROJECT_ROOT_NAMESPACE}:registry=${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/npm/"
+          echo "${CI_API_V4_URL#http*:}/projects/${CI_PROJECT_ID}/packages/npm/:_authToken=\${CI_JOB_TOKEN}"
+        } >> .npmrc
+      fi
+    - echo "Created the following .npmrc:"; cat .npmrc
+
+    # Extract a few values from package.json
+    - NPM_PACKAGE_NAME=$(node -p "require('./package.json').name")
+    - NPM_PACKAGE_VERSION=$(node -p "require('./package.json').version")
+
+    # Validate that the package name is properly scoped to the project's root namespace.
+    # For more information, see https://docs.gitlab.com/ee/user/packages/npm_registry/#package-naming-convention
+    - |
+      if [[ ! $NPM_PACKAGE_NAME =~ ^@$CI_PROJECT_ROOT_NAMESPACE/ ]]; then
+        echo "Invalid package scope! Packages must be scoped in the root namespace of the project, e.g. \"@${CI_PROJECT_ROOT_NAMESPACE}/${CI_PROJECT_NAME}\""
+        echo 'For more information, see https://docs.gitlab.com/ee/user/packages/npm_registry/#package-naming-convention'
+        exit 1
+      fi
+
+    # Compare the version in package.json to all published versions.
+    # If the package.json version has not yet been published, run `npm publish`.
+    - |
+      if [[ $(npm view "${NPM_PACKAGE_NAME}" versions) != *"'${NPM_PACKAGE_VERSION}'"* ]]; then
+        npm publish
+        echo "Successfully published version ${NPM_PACKAGE_VERSION} of ${NPM_PACKAGE_NAME} to GitLab's NPM registry: ${CI_PROJECT_URL}/-/packages"
+      else
+        echo "Version ${NPM_PACKAGE_VERSION} of ${NPM_PACKAGE_NAME} has already been published, so no new version has been published."
+      fi

spec/lib/gitlab/ci/templates/npm_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'npm.latest.gitlab-ci.yml' do
+  subject(:template) { Gitlab::Template::GitlabCiYmlTemplate.find('npm.latest') }
+
+  describe 'the created pipeline' do
+    let_it_be(:user) { create(:admin) }
+
+    let(:repo_files) { { 'package.json' => '{}', 'README.md' => '' } }
+    let(:modified_files) { %w[package.json] }
+    let(:project) { create(:project, :custom_repo, files: repo_files) }
+    let(:pipeline_branch) { project.default_branch }
+    let(:pipeline_tag) { 'v1.2.1' }
+    let(:pipeline_ref) { pipeline_branch }
+    let(:service) { Ci::CreatePipelineService.new(project, user, ref: pipeline_ref ) }
+    let(:pipeline) { service.execute!(:push) }
+    let(:build_names) { pipeline.builds.pluck(:name) }
+
+    def create_branch(name:)
+      ::Branches::CreateService.new(project, user).execute(name, project.default_branch)
+    end
+
+    def create_tag(name:)
+      ::Tags::CreateService.new(project, user).execute(name, project.default_branch, nil)
+    end
+
+    before do
+      stub_ci_pipeline_yaml_file(template.content)
+
+      create_branch(name: pipeline_branch)
+      create_tag(name: pipeline_tag)
+
+      allow_any_instance_of(Ci::Pipeline).to receive(:modified_paths).and_return(modified_files)
+    end
+
+    shared_examples 'publish job created' do
+      it 'creates a pipeline with a single job: publish' do
+        expect(build_names).to eq(%w[publish])
+      end
+    end
+
+    shared_examples 'no pipeline created' do
+      it 'does not create a pipeline because the only job (publish) is not created' do
+        expect { pipeline }.to raise_error(Ci::CreatePipelineService::CreateError, 'No stages / jobs for this pipeline.')
+      end
+    end
+
+    context 'on default branch' do
+      context 'when package.json has been changed' do
+        it_behaves_like 'publish job created'
+      end
+
+      context 'when package.json does not exist or has not been changed' do
+        let(:modified_files) { %w[README.md] }
+
+        it_behaves_like 'no pipeline created'
+      end
+    end
+
+    %w[v1.0.0 v2.1.0-alpha].each do |valid_version|
+      context "when the branch name is #{valid_version}" do
+        let(:pipeline_branch) { valid_version }
+
+        it_behaves_like 'publish job created'
+      end
+
+      context "when the tag name is #{valid_version}" do
+        let(:pipeline_tag) { valid_version }
+        let(:pipeline_ref) { pipeline_tag }
+
+        it_behaves_like 'publish job created'
+      end
+    end
+
+    %w[patch-1 my-feature-branch v1 v1.0 2.1.0].each do |invalid_version|
+      context "when the branch name is #{invalid_version}" do
+        let(:pipeline_branch) { invalid_version }
+
+        it_behaves_like 'no pipeline created'
+      end
+
+      context "when the tag name is #{invalid_version}" do
+        let(:pipeline_tag) { invalid_version }
+        let(:pipeline_ref) { pipeline_tag }
+
+        it_behaves_like 'no pipeline created'
+      end
+    end
+  end
+end