CODEWITHSUNDEEP
buildrepositorybazelworkspace
Konstantin Erman
Konstantin Erman

Reputation: 601

Is there a way to make Bazel work with transitive repositories?

I work with a massive codebase distributed across many repositories and using even more third-party dependencies. The goal is to make the build hermetic and I contemplate using Bazel to achieve it. On the one hand, Bazel has git_repository rule to refer to the external repos in the WORKSPACE file. On the other hand, WORKSPACE files are not loaded recursively, so to get to indirect dependencies I need to build all inclusive WORKSPACE file somehow. I wonder if somebody already tackled that problem using Bazel or some other existing tools. Is there a way to expand the WORKSPACE as part of the build? May be WORKSPACE can #include other (generated) files?

Upvotes: 2

Views: 2995

Answers (1)

Brian Silverman
Brian Silverman

Reputation: 3838

WORKSPACE files can load and then call macros, which gives similar functionality to #include.

A common pattern is each project having a macro which calls macros (for dependencies on other projects) and creates *_archive rules (for dependencies directly on files to download) so it builds. For example, protobuf has protobuf_deps to implement this pattern. If you create a repository with protobuf (using git_repository, or http_archive, or any of the other repository rules), then you can load that macro and call it, and you'll automatically get all the transitive dependencies.

For example (from Chromium):

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
# This com_google_protobuf repository is required for proto_library rule.
# It provides the protocol compiler binary (i.e., protoc).
http_archive(
    name = "com_google_protobuf",
    strip_prefix = "protobuf-master",
    urls = ["https://github.com/protocolbuffers/protobuf/archive/master.zip"],
)
load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
protobuf_deps()

I'm showing http_archive because it's easier to work with, but you can easily change it to git_archive if you want.

Another common pattern which makes this all work is the way protobuf_deps checks native.existing_rule before creating each http_archive. That allows you to instantiate a specific version (or from a specific source, etc) of the dependency directly in your WORKSPACE file to override the one protobuf would otherwise bring in.

Upvotes: 2

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