How can you set up dynamically loaded library dependencies in bazel?

Question

Suppose I have a unit test that uses dlopen to load and call code from a provided shared library

int main(int argc, char* argv[]) {
  const char* library = argv[1];
  // calls dlopen with library and does some testing
}

Given the declared library

cc_library(
    name = "a",
    srcs = ["a.cpp"],
    visibility = ["//visibility:public"],
)

Is there any way I can use cc_test to set up the unit test to run with the location of library a passed in as an argument? (Preferably also in a platform independent way so that I don't have to worry about what suffix is used for the library)

Answer 1

You might be able to write a custom skylark rule that accesses runfiles (related discussion here).

Hacking something together:

BUILD:

load("//:foo.bzl", "runfiles")

cc_binary(
    name = "liba.so",
    srcs = [ "a.cc" ],
    linkshared = 1,
)

runfiles(
    name = "runfiles",
    deps = [ ":liba.so" ],
)

foo.bzl:

def _impl(ctx):
  for dep in ctx.attr.deps:
    print(dep.files_to_run.executable.path)

runfiles = rule(
  implementation = _impl,
  attrs = {
    "deps": attr.label_list(allow_files=True),
  }
)