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Development Notes

Project Layout

This repo attempts to keep language-specific dependencies separate, meaning if you use stackb/rules_proto for C++, you shouldn't need to transitively pull in scala deps, for example.

  • //rules:*all*: core starlark rules and providers. Bzl files here should not load any language-specific things.
  • //rules/{LANG}:*all*: language-specific rules. Bzl files here may reference language-specific deps.
  • //cmd/gazelle: a copy of the gazelle frontend with some minor modifications. The langs.go file is added which loads the protobuf language. This copy of gazelle ends up being built by the standard go toolchain for the proto_repository rule.
  • //cmd/depsgen: a helper tool used by the depsgen rule (see //deps:*) that generates .bzl files based on the transitive set of proto_repository rules.
  • //cmd/examplegen: a helper tool that generates markdown and a _test.go file used by the gazelle_testdata_example rule (see //example/golden:*).
  • //cmd/gencopy: a helper tool that is used to copy generated files back into the source tree.
  • //example/...: example gazelle directives and rules.
  • //deps:*: contains the //deps:BUILD.bazel files where all project dependencies are declared as proto_repository rules. These are linked together via their deps attribute. Each depsgen(name = "foo") rule in that file is used to create the corresponding deps/foo_deps.bzl, which is generated and then copied back into the source tree. Use make deps target to regenerate these files.
  • go.mod, go.sum. The are the inputs to generate the go_deps.bzl file. Use bazel run //:update_go_deps to regenerate this file.
  • //language/protobuf: contains the protobuf language extension. The label @build_stack_rules_proto//language/protobuf should be referenced in the gazelle_binary rule.
  • //language/example contains a no-op gazelle extension that can be used an empty template.
  • //pkg/...: contains all go packages for tools.
  • //pkg/language/protobuf: contains the actual protobuf gazelle extension implementation.
  • //pkg/language/noop: contains an empty extension that can be used as a starting template.
  • //pkg/protoc: a core package that defines the registry, language, rule interfaces, and much of the implementation. I'm not sure why I named it protoc.
  • //pkg/rule/...: rule implementations.
  • //plugin/...: directories here contain proto_plugin rules. In some cases, the plugin tool is built here, possibly depending on language-specific deps. For example, the //plugin/stephenh/ts-proto tool requires NPM dependencies.
  • //third_party/...: third party BUILD rules. TODO: get rid of this.
  • //toolchain. The toolchain definition used by the proto_compile rule.

Vendoring Files

The vendor/ tree is used by the standard go build toolchain when constructing the binary for the proto_repository rule. If new dependencies are added to the tool, they may need to be also added to vendor/. Use make tidy for this. That target will run the vendor command and then remove any BUILD.bazel files. This is needed because the //:all_files target attempts to glob up everything in the vendor/ directory. This does not work correctly if there are BUILD.bazel files in vendor. These files are also listed in the .gitignore file.

Debugging gazelle_testdata_example tests.

The target //example/golden:golden_test runs a test foreach subdirectory of example/golden/testdata/. These tests stage all the BUILD.in files, optionally using a .gazelle.args file to run gazelle. It then compares the actual BUILD files produced to the BUILD.out files. These are generally straightforward to debug as a diff is printed out if the test fails.

Use bazel query //example/golden:all to see all the actual tests in this package.

The tests defined by gazelle_testdata_example glob up one of the testdata/scala/ directories and generates a _test.go file. Use bazel build //example/golden:scala to print out the generated test file (cat bazel-bin/example/golden/scala_test.go).

This type of test packages up the BUILD.out files and uses go_bazel_test to actually run bazel build ... on it. So, the :golden_test target is used to assert that the correct gazelle output is generated, while :scala_test is used to assert that the outbut actually builds.

The effective WORKSPACE file is a concatenation of the workspace_template (e.g. prebuilt.WORKSPACE) and the one in the testdata example dir.

One way to debug these kinds of tests is to open an editor in the effective directory where the test is constructed (this will be printed out if it fails). For example (cd /private/var/tmp/_bazel_i868039/7b08591af2b3d71f45f2e4029050db37/bazel_testing/bazel_go_test/main && code .). You can then use bazel build directly in this space to explore what's going on.