Generate granular Bazel targets using module extension

[mering]

It would be great if Bazel toolchains could be used to run the actual build instead of building via make/ninja.

It could work the following way:

# CMakeLists.txt
add_library(example_lib example.cc)

# MODULE.bazel
foreign = load("@rules_foreign_cc//extension.bzl")
foreign.cmake(
    url = "https://example.com/lib.tgz",
)
use(foreign, "com_example_lib")

# BUILD
cc_library(
    deps = ["@com_example_lib//example_library"]
)

The extension would create and execute a repository rule to download the project and run CMake.

CMake would need an additional Bazel generator (in addition to Make/Ninja).

[jsharpe]

I'm not sure how feasible a Bazel generator in CMake actually is; as far as I know CMake doesn't have strict dependencies and so can't tell you for a given file what all the inputs should be and so I'm not sure you can reliably generate bazel files from a CMake project.

Even if it is feasible, who would be the maintainer / owner of this code? It would have to live in the CMake codebase. I believe Conan used to have a bazel generator but I think its become unmaintained / removed from the latest version of Conan which suggests that there is a lack of appetite from the CMake side to maintain something like this.

[mering]

CMake does have strict dependencies (at least for source files) on a library target level. I would suggest to use the same granularity in the generated output.

The CMake Bazel generator would also be suitable standalone. Of course all code has to be maintained by someone but this is independent from the repository it lives in.