portal-co / cc_config

Generally useful stuff for C builds using Bazel

cc_config

Table of Contents

• repo paths
• module name & version makevars

Generally useful stuff for C builds

repo paths

Defines make variables that expand to paths suitable for passing with -I in cc rules. For example copts = ["-I$(@foo)/include"].

Usage:

Add to MODULE.bazel: bazel_dep(name = "cc_config", version = "1.0.0")

Then instantiate the macro in a BUILD.bazel file. List one target for each bazel_dep module for which you need an include path. Since these are dependencies, you may need to instantiate a separate target for dev dependencies.

//:BUILD.bzl

load("@cc_config//:MACROS.bzl", "repo_paths")
PROD_REPOS = [
    "@uthash//src:uthash",
    "@liblogc//src:logc"
]

repo_paths(
    name = "repo_paths",
    repos = PROD_REPOS
)

repo_paths(
    name = "test_repo_paths",
    repos = PROD_REPOS + [
        "@unity//src:unity" ## test-only
    ]
)

In this example, module unity is listed as a dev_dependency in MODULE.bazel.

This defines one make variable for each repository listed in the repos attr. Add the repo_paths target label to the toolchains attribute and you can then use them as e.g. $(@uthash), $(@liblogc), etc. Note that @ is included in the string. As a special case, $(@) resolves to the "current" repo.

The make vars expand to the path, not just the repo identifier. In particular the expansion includes the external/ prefix for external repos.

For example, you might have:

@foo//src:BUILD.bazel

cc_library(
...
    deps = ["@liblogc//src:logc"],
    copts = ["-I$(@)/src", "-I$(@liblogc)/src"],
    toolchains = ["//:repo_paths"]
    ...
)

Assuming the versions of both @foo @liblogc are 1.0.0, if this target is built from within the foo repo, the expansions are:

• $(@) expands to ., yielding -I./src

• $(@liblogc)/src expands to external/liblogc~1.0.0/src

If this target is built as an external repo (i.e. module foo is listed as a bazel_dep for some other module):

• $(@) expansion includes external, giving -Iexternal/foo~1.0.0/src

• $(@liblogc)/src expands as above

module name & version makevars

Version 2 adds make variables MODULE_NAME and MODULE_VERSION, whose values are derived from Bazel’s native.module_name() and native.module_version(), respectively.

This allows C/C++ code to integrate the version string from MODULE.bazel, like so in BUILD.bazel (assuming one has configured //:repo_paths as directed above):

copts = ["'-D$(MODULE_NAME)_VERSION=\"$(MODULE_VERSION)\"'"]
...
toolchains = ["//:repo_paths"]

which generates on the cmd line: '-DMYMODULE_VERSION="2.1.2"'

And in source code: const char *mymodule_version = MYMODULE_VERSION;