### Problem to solve <!-- What problem do we solve? --> For maximum correctness, CI/CD systems usually rebuild everything from scratch on every run. This is considered safer since artifacts from one pipeline won't negatively impact subsequent pipelines. e.g. This is a classic problem in some legacy uses on Jenkins, where each pipeline run modifies the runner state. If a build fails, you never know for sure if it was because of something in the new code, or if something leftover from a previous run. Likewise, pipelines aren't completely repeatable since you never really know what the complete state was when it was run. But re-running everything from scratch is very slow. We try to improve upon this by using caches and shared artifacts, but there's only so far that approach can go. [Bazel](https://bazel.build/) is a good example of tackling it a different way. Bazel speeds up builds by only rebuilding what is necessary. On the surface, that sounds a lot like just having a cache and doing an incremental build. But the main difference is that Bazel is really good at not only being "fast", but also "correct". It's much more reliable than traditional Makefiles or build scripts which are notorious for occasionally having to do a `make clean` because they get into some inconsistent state they can't recover from. Going further, since you know exactly what has changed, you can be more selective in doing incremental tests and have the confidence that skipped tests were truly unnecessary. In an ideal world, after a minor change, the build and test should only take a few seconds. When it gets fast enough, it could even be triggered via an editor on every change before being committed to git at all. ### Intended users <!-- Who will use this feature? If known, include any of the following: types of users (e.g. Developer), personas, or specific company roles (e.g. Release Manager). It's okay to write "Unknown" and fill this field in later. * [Rachel (Release Manager)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#rachel-release-manager) * [Parker (Product Manager)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#parker-product-manager) * [Delaney (Development Team Lead)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#delaney-development-team-lead) * [Sasha (Software Developer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer) * [Presley (Product Designer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#presley-product-designer) * [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer) * [Sidney (Systems Administrator)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sidney-systems-administrator) * [Sam (Security Analyst)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sam-security-analyst) * [Dana (Data Analyst)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#dana-data-analyst) Personas are described at https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/ --> * [Delaney (Development Team Lead)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#delaney-development-team-lead) * [Sasha (Software Developer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer) * [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer) ### Further details <!-- Include use cases, benefits, and/or goals (contributes to our vision?) --> ### Proposal <!-- How are we going to solve the problem? Try to include the user journey! https://about.gitlab.com/handbook/journeys/#user-journey --> ### Permissions and Security <!-- What permissions are required to perform the described actions? Are they consistent with the existing permissions as documented for users, groups, and projects as appropriate? Is the proposed behavior consistent between the UI, API, and other access methods (e.g. email replies)?--> ### Documentation <!-- See the Feature Change Documentation Workflow https://docs.gitlab.com/ee/development/documentation/feature-change-workflow.html Add all known Documentation Requirements here, per https://docs.gitlab.com/ee/development/documentation/feature-change-workflow.html#documentation-requirements If this feature requires changing permissions, this document https://docs.gitlab.com/ee/user/permissions.html must be updated accordingly. --> ### Availability & Testing <!-- This section needs to be retained and filled in during the workflow planning breakdown phase of this feature proposal, if not earlier. What risks does this change pose to our availability? How might it affect the quality of the product? What additional test coverage or changes to tests will be needed? Will it require cross-browser testing? Please list the test areas (unit, integration and end-to-end) that needs to be added or updated to ensure that this feature will work as intended. Please use the list below as guidance. * Unit test changes * Integration test changes * End-to-end test change See the test engineering planning process and reach out to your counterpart Software Engineer in Test for assistance: https://about.gitlab.com/handbook/engineering/quality/test-engineering/#test-planning --> ### What does success look like, and how can we measure that? <!-- Define both the success metrics and acceptance criteria. Note that success metrics indicate the desired business outcomes, while acceptance criteria indicate when the solution is working correctly. If there is no way to measure success, link to an issue that will implement a way to measure this. --> ### What is the type of buyer? <!-- Which leads to: in which enterprise tier should this feature go? See https://about.gitlab.com/handbook/product/pricing/#four-tiers --> ### Links / references - https://blog.bazel.build/2016/01/27/continuous-integration.html - https://blog.donbowman.ca/2018/09/03/navigating-the-restrictions-of-ci-and-bazel/ - https://medium.com/@bamnet/using-bazel-on-gitlab-ci-fe59cad2db50 <!-- triage-serverless v3 PLEASE DO NOT REMOVE THIS SECTION --> *This page may contain information related to upcoming products, features and functionality. It is important to note that the information presented is for informational purposes only, so please do not rely on the information for purchasing or planning purposes. Just like with all projects, the items mentioned on the page are subject to change or delay, and the development, release, and timing of any products, features, or functionality remain at the sole discretion of GitLab Inc.* <!-- triage-serverless v3 PLEASE DO NOT REMOVE THIS SECTION -->