Building Makefile using bazel

Question

I am trying to build Makefile of a submodule in a bazel project. I see that bazel does provide genrule to execute bash command. I am facing two issues currently -

Answer 1

Instead of rolling your own genrule to build a (presumably C++) project that uses a Makefile, check out rules_foreign_cc instead. rules_foreign_cc is used by envoy and other various large C++ programs to build external CMake and Make based dependencies.

See the simple_make example. In it, you would first make a filegroup to collect all the sources and files related to the project to be built, including the Makefile itself:

filegroup(
    name = "sources",
    srcs = glob(["**"]),
    visibility = ["//simple_make:__subpackages__"],
)

Then, call rules_foreign_cc's make rule, which also comes with other make-specific attributes like prefix, make_env_vars, and even a way to override the entire make command with make_commands. In this example, we're just using the lib_source and static_libraries attributes:

load("@rules_foreign_cc//tools/build_defs:make.bzl", "make")

make(
    name = "make_lib",
    lib_source = "//simple_make/code:sources",
    static_libraries = ["liba.a"],
)

Finally, run bazel build //package/to:make_lib to invoke the make rule.

How do I update update submodule before executing genrule?

Try not to do this especially if it updates the sources of the project in-place. genrules and other rules should not modify the state of your sources during a build, but instead only build output files. Consider running a separate script to update submodules prior to the build.