Developing with Bazel

We’ve migrated the cockroach build system to Bazel. Bazel is a modern build system with better performance characteristics and correctness guarantees than we currently have with make/go build. Today, you can perform almost all day-to-day CRDB dev tasks with Bazel rather than with make. make is deprecated and we will remove this option for building Cockroach at some point in the next release cycle.

For the few tasks that you can't/don't know how to do with Bazel, please ask a question or contribute a solution. The Bazel migration is actively in progress and we always accept contributions even for minor/QOL improvements.

NOTE: for specific debugging tips on:
- Build failures, see “How to ensure your code builds with Bazel”
- Test failures, see “How to ensure your tests can run in the Bazel sandbox”

Prerequisites

Follow the directions on "Getting and building CockroachDB from source" or "Building from source on macOS" to get your development environment set up.

Getting started

Introduction to dev

dev is a light wrapper around Bazel that is well-suited to specific CRDB development tasks. Properly, when we say dev, we’re referring to the Go binary whose source lives in cockroach/pkg/cmd/dev, side-by-side with the Cockroach source. At the top level of the repo there is a wrapper script also called dev whose only job is to build pkg/cmd/dev and then invoke it with the passed-in arguments. This means that you can always type ./dev to run the version of dev at the commit you’ve checked out, which is typically what you want to do.

Note that dev is meant to supplement bazel rather than replace it. dev makes certain tasks easier than bazel, but simple builds and tests are easy enough to run via bazel directly.

Doctor, doctor

Before trying to build anything, run the following:

If dev notices any issues with your system that might prevent you from being able to build, it will let you know and tell you how to fix it. Make sure to run dev doctor before you ask for help just in case it catches something you didn’t know about.

NOTE: dev will take a while to run the first time you execute it since it needs to build itself. Be patient.

First steps: building cockroach

Start by building cockroach-short as follows:

./dev build short also works and will stage the binary at ./cockroach. Bazel will pretty-print build output to the terminal.

You can also build the full cockroach binary which includes the Javascript build.

./dev build (or equivalently, ./dev build cockroach) will do the same and will stage the binary at ./cockroach like above.

dev build is a light wrapper for bazel build that supports aliases for common targets (for example, ./dev build crlfmt instead of the harder-to-remember bazel build @com_github_cockroachdb_crlfmt//:crlfmt). dev also copies binaries out of the Bazel output directories for you into your workspace; for example, bazel build pkg/cmd/cockroach-short puts the binary in _bazel/bin/pkg/cmd/cockroach-short/cockroach-short_/cockroach-short, but if you dev build short the binary will be staged at ./cockroach instead.

Run ./dev help build for more information about what you can do with dev build. Note that you can pass additional arguments directly to bazel build by adding them after --:

dev lets you cross-compile with the --cross option, as in:

--cross takes an optional argument which is the platform to cross-compile to: --cross=linux, --cross=windows, --cross=macos, --cross=linuxarm, --cross=macosarm. dev will copy the built binaries into the artifacts directory in this case. Note that cross-building requires a docker-compatible system installed like Rancher Desktop.

For more debugging tips on building with Bazel, see “How to ensure your code builds with Bazel”.

Running tests

You can run all tests in a given package (for example, pkg/sql) with:

bazel test pkg/sql/... will instead run all tests under the pkg/sql directory recursively, including all the tests under pkg/sql/types and pkg/sql/rowinfra among others.

If the test passes, you’ll see a brief message indicating which tests were run and their status:

If the test doesn’t pass, Bazel will print the location of the test’s log file:

You can examine that file to see the complete logs for the test.

./dev test is provided as a shorthand for bazel test with some additional conveniences. Run ./dev test with the name of one or more packages to execute all tests from those packages:

Tips and tricks

• dev test has a --stress flag for running tests under stress and --race for running tests with the race detector enabled.

• Next to the test.log file produced by your test, you can find a test.xml file. This file contains specific information on each test run and its status, as well as timing information.

• The -v argument to dev test will result in more verbose logging as well as more detailed information written to the test.xml. You can make this the default behavior on your machine by adding test --test_env=GO_TEST_WRAP_TESTV=1 to your .bazelrc.user file.

• As with dev build, dev test allows you to pass additional arguments directly to Bazel by putting them after --: for example, dev test pkg/sql/types -- --verbose_failures --sandbox_debug.

• To get test results printed as tests are being run add -v -- --test_output streamed to the test command. Note that this reduces test parallelism.

• To attach a debugger to a hung dev test process tack -- -c dbg to the end of your command and it will disable stripping which breaks dlv (Cannot debug `go_test` targets · Issue #2313 · bazelbuild/intellij).

• For more tips on debugging test failures, see “How to ensure your tests can run in the Bazel sandbox”

Other tasks

To pass -gcflags to the build of a library, add gc_goopts = ["S"], to the go_library target in the BUILD.bazel file for the package you’re interested in, then run devas usual.

To override a dependency for local builds when doing automation, update the go_repository() declaration in DEPS.bzl for your dependency to point to a new remote and commit (see top-level comment in DEPS.bzl for more information), then build/test as usual.

General dev tips

The top-level dev script uses Bazel to build pkg/cmd/dev before running unless another dev binary with the same increasing integer ID has already been built. Generally dev will invoke the dev binary “as of” that commit, which should usually be the correct behavior. However, if the default behavior does not work for some reason, you can find all the built versions of dev under bin/dev-versions.

A (hopefully) fast and error proof dev workflow

1. Switch to a new branch

2. If your workflow involves an IDE, generate your protos ./dev gen protobuf

• Your IDE relies on generated files for many tasks (e.g. code navigation, IntelliSense, debugging), and will complain unless you have re-generated those files.

  • If you need to re-generate all generated go files, use the slower ./dev gen go

  • If the above fails, run the slowest ./dev gen to update all of your generated files.

  • If this fails too, try git clean. If GOLAND complains about dependent packages, try git clean -dfx pkg instead. Then repeat the steps above.

  • You may recall that with make , this step was not necessary. If you’re curious why, see this slack thread.

3. If your workflow involves UI development, you’ll want additionally do the following:

4. Write some code!

• If you don’t have crlfmt already, you’ll need to ./dev build crlfmt to use it for formatting.

• If you add new files or imports, run ./dev gen bazel before compiling or running a test. compilepkg: missing strict dependencies: is usually the indicator that ./dev gen bazel needs to be re-run.

  • to skip this step, see tip below on ALWAYS_RUN_GAZELLE

• Build the binary: ./dev build short

5. Run a test

• On an IDE: your normal workflow should work if your generated files are up to date (See step 2).

• From the command line: ./dev test [path/to/pkg] --filter [test_name]

6. Before opening/updating a PR:

• Run ./dev lint --short (maybe additionally make lintshort as dev's linter doesn’t have 100% coverage yet)

• Assert your workspace is clean by running ./dev gen bazel . If you modified other generated files, run the appropriate ./dev gen [file_type] command.

Rapidly iterating with dependencies

The file DEPS.bzl tells Bazel how to download dependencies. For production, we point to .zip files that are mirrored on our internal infrastructure, protecting us against dependency yanking/”left-pad”-style failures. However, for local development, you have a few other options.

The top-level comment at the top of DEPS.bzl explains how to point to a custom remote for a dependency, for example:

In this example, github.com/cockroachdb/sentry-go will point to the given remote and commit instead of using the production version of the library. Note the remote can be either a normal git https remote or it can be a local clone.

In this case, iterating can be cumbersome as you have to update the commit whenever you want to pull a new version of the dependency. You can use the Bazel flag --override_repository to optimize for this case, so you can make changes locally on your machine and immediately re-build cockroach with your latest local changes instead of updating the dependency to point to a new commit whenever you want to test your changes. The following explanation is copy-pasted from internal Slack:

The process doesn't vary per dependency so I'll demonstrate with github.com/google/btree. First I'm going to clone that repo and check out the version of the code I want.

Back in cockroach I update .bazelrc.user to point to the clone I just made. The form of the flag is --override_repository=REPO_NAME=/path/to/local/repo. The flag tells Bazel to ignore where REPO_NAME "really is", and instead just use the local clone. Note that DEPS.bzl declares the "name of the repo" which in this context is Java-style, like com_github_google_btree. I am going to add it to .bazelrc.user so I don't have to remember to add the flag every time, although it's a normal Bazel flag so you can just include it on the command-line too.

The first thing I'll do is build just to demonstrate that what I've done so far is a no-op.

Oh, whoops. The BUILD.bazel file and WORKSPACE files are missing because I didn't run Gazelle. Let me fix that. From back in the btree directory:

Now the build will succeed back in cockroach.

You only need to use gazelle to generate files once, unless as part of your changes you create a new file, update a dependency, or do something else that changes the actual build process. In that case you can re-run gazelle to fix it.

When you're done with testing your local changes, you can remove the --override_repository line from .bazelrc.user.

General Bazel tips

• Bazel has a configuration file called .bazelrc. You can put a global configuration file at ~/.bazelrc or a per-repository file at .bazelrc.user in the root of your cockroach repo.

• Stripping: stripping of symbols in built binaries is enabled by default, as disabling stripping slows down linking drastically. You can disable stripping with the Bazel flags -c dbg or -c opt (if you are making a binary you wish to debug, you will use -c dbg), or you can force-enable it with --strip=never.

  • Binaries built with dev build --cross, by the release process, or for nightly roachtests are built with -c opt and will therefore be unstripped.

• While Bazel is the “official” build system, you do not have to use it for normal development. For example, many people do development from their IDE’s, and this is expected to “just work”. Note that since not all generated code is checked into the repo, you’ll first have to generate code to get much of it to build from a non-Bazel build system. We refer to this as the “escape hatch”. This escape hatch is specifically supported so if you have difficulty running a test in another build system after generating code, that’s a bug you should report. You can run the following commands to make this happen:

  • dev gen go

    • Generates all .go code that goes into the build, including cgo code

  • dev gen cgo

    • Generates some stub files that tell cgo how to link in the c-deps; part of dev gen go

  • dev gen protobuf

    • Generates all .pb.go/.pb.gw.go files; part of dev gen go

• Tired of running ./dev gen bazel? Set the ALWAYS_RUN_GAZELLE env-var to automatically run gazelle before every dev test or dev build incantation. Note this does add a tiny delay – noticeable when iterating on small tests through dev test.

  • i.e. echo 'export ALWAYS_RUN_GAZELLE=1' >> ~/.zshrc

  • Note that gazelle is only a subset of the aactions that dev gen bazel performs. This by itself is able to handle most updates to the code, but is not able to handle things like vendoring new dependencies (dev gen bazel can do this for you).

• If you have ccache installed, bazel will fail with an error like ccache: error: Failed to create temporary file for /home/alyshanjahani/.ccache/tmp/message_li.stdout: Read-only file system. To avoid this you should get the ccache links out of your PATH manually (i.e. uninstall ccache), and then you might need to do bazel clean --expunge.

  • Alternatively, if you would like to use Bazel with ccache, you can enable support for writing outside the sandbox by adding the following to your $HOME/.bazelrc or <repo>/.bazelrc.user file:
    - For MacOS/Darwin:

    build --sandbox_writable_path=/Users/<USER>/Library/Caches/ccache/

    - For Linux:

    build --sandbox_writable_path=/home/<USER>/.ccache

dev vs. Bazel

You can always use bazel directly instead of going through dev but there are some things you might want to keep in mind:

• You should still ask dev doctor if your machine is up-to-snuff before you try to bazel build. The checks it performs aren’t dev-specific. dev doctor also sets up a local cache for you.

• dev prints out the (relevant) calls to bazel it makes before it does so. You can therefore run dev once just to learn how to ask Bazel to perform your build/test and then just directly call into bazel on subsequent iterations.

  • When running tests under stress, race, or --rewrite, dev does the legwork to invoke with the necessary flags with bazel. This involves running under another binary (stress), running with certain gotags (race), or allowing certain paths outside the bazel sandbox to be written to (testdata). Feel free to see the actual bazel command invoked and tweak as necessary.

• If you want to build a test without running it, you must include the the --config test argument to bazel build. (dev takes care of this for you if you are using it.)

Managing CPU resources available to a test under Bazel

In Bazel, all tests under a given Go package belong to the same test target. Test targets can be sharded into multiple shards and each shard will run a subset of the tests in a given test target. Shards can run in parallel but tests within each shard run sequentially.

By default, each shard gets 1 CPU core and as a result each test has 1 CPU core available to it. This can be adjusted by adding the following to the go_test rule for that test target (found in BUILD.bazel)

Note: Adjusting the number of CPU cores using the method above will adjust the number of CPU cores available to all tests in that test target. If you need to adjust the number of cores for a single test (few tests), extract it into a separate package and adjust the number of cores there to avoid reserving extra CPU cores for tests that don’t need them.