From adcea4ddb7970c22b4dd5e2380ab89e6745054fd Mon Sep 17 00:00:00 2001
From: Lukas Eipert <leipert@gitlab.com>
Date: Wed, 22 Apr 2020 15:07:49 +0200
Subject: [PATCH] Danger: Add bundle size analysis

Adding a new danger job which analyses and compares the current MRs
bundle size to the bundle size of the commit on master it is trying to
merge into.

The tool itself is managed in:
https://gitlab.com/gitlab-org/frontend/playground/webpack-memory-metrics
---
 .gitlab/ci/frontend.gitlab-ci.yml | 19 ++++++++++++++++
 .gitlab/ci/rules.gitlab-ci.yml    |  6 +++++
 danger/bundle_size/Dangerfile     | 38 +++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+)
 create mode 100644 danger/bundle_size/Dangerfile

diff --git a/.gitlab/ci/frontend.gitlab-ci.yml b/.gitlab/ci/frontend.gitlab-ci.yml
index 1538352a8812..860ca04813a5 100644
--- a/.gitlab/ci/frontend.gitlab-ci.yml
+++ b/.gitlab/ci/frontend.gitlab-ci.yml
@@ -335,3 +335,22 @@ webpack-dev-server:
     expire_in: 31d
     paths:
       - webpack-dev-server.json
+
+bundle-size-review:
+  extends:
+    - .default-retry
+    - .frontend:rules:bundle-size-review
+  image: registry.gitlab.com/gitlab-org/gitlab-build-images:danger
+  stage: test
+  needs: ["gitlab:assets:compile pull-cache"]
+  script:
+    - mkdir -p bundle-size-review
+    - cp webpack-report/index.html bundle-size-review/bundle-report.html
+    - yarn global add https://gitlab.com/gitlab-org/frontend/playground/webpack-memory-metrics.git
+    - danger --dangerfile=danger/bundle_size/Dangerfile --fail-on-errors=true --verbose --danger_id=bundle-size-review
+  artifacts:
+    when: always
+    name: bundle-size-review
+    expire_in: 31d
+    paths:
+      - bundle-size-review
diff --git a/.gitlab/ci/rules.gitlab-ci.yml b/.gitlab/ci/rules.gitlab-ci.yml
index 383aca0043b7..c0ea616c2d1e 100644
--- a/.gitlab/ci/rules.gitlab-ci.yml
+++ b/.gitlab/ci/rules.gitlab-ci.yml
@@ -335,6 +335,12 @@
       changes: *frontend-dependency-patterns
       allow_failure: true
 
+.frontend:rules:bundle-size-review:
+  rules:
+    - if: '$DANGER_GITLAB_API_TOKEN && $CI_MERGE_REQUEST_IID && $CI_MERGE_REQUEST_TARGET_BRANCH_NAME == "master"'
+      changes: *frontend-patterns
+      allow_failure: true
+
 ################
 # Memory rules #
 ################
diff --git a/danger/bundle_size/Dangerfile b/danger/bundle_size/Dangerfile
new file mode 100644
index 000000000000..e2621360c7ff
--- /dev/null
+++ b/danger/bundle_size/Dangerfile
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+analysis_result = "./bundle-size-review/analysis.json"
+markdown_result = "./bundle-size-review/comparison.md"
+
+# Executing the webpack-entry-point-analyser
+# We would like to do that in the CI file directly,
+# but unfortunately the head_commit SHA is not available
+# as a CI variable due to our merge into master simulation
+analyze_cmd = [
+  "webpack-entry-point-analyser",
+  "--from-file ./webpack-report/stats.json",
+  "--json #{analysis_result}",
+  " --sha #{gitlab&.head_commit}"
+].join(" ")
+
+# execute analysis
+`#{analyze_cmd}`
+
+# We are executing the comparison by comparing the start_sha
+# to the current pipeline result. The start_sha is the commit
+# from master that was merged into for the merged pipeline.
+comparison_cmd = [
+  "webpack-compare-reports",
+  "--from-sha #{gitlab.mr_json["diff_refs"]["start_sha"]}",
+  "--to-file #{analysis_result}",
+  "--html ./bundle-size-review/comparison.html",
+  "--markdown #{markdown_result}"
+].join(" ")
+
+# execute comparison
+`#{comparison_cmd}`
+
+comment = `cat #{markdown_result}`
+
+markdown(<<~MARKDOWN)
+    #{comment}
+MARKDOWN
-- 
GitLab