How can I pass a specific macro to each compile in bazel? - bazel

Question

Here's an easy version of the BUILD file:
cc_library(
name = "ab",
srcs = ['a.c', 'b.c', 'logger.h'],
)
logger.h contains the implementation of a logging function that uses the macro XOC_FILE_ID. XOC_FILE_ID has to contain the name of the source file.
Using __FILE__ instead would not help because __FILE__ expands to the string "logger.h" inside the file logger.h.
That's why I need to compile these files with different defines:
gcc -c [...] -DXOC_FILE_ID="a.c" a.c
gcc -c [...] -DXOC_FILE_ID="b.c" b.c
My failed approaches:
set the attribute local_defines using the value{source_file}: local_defines = ['XOC_FILE_ID="{source_file}"]: does not get replaced
set the attribute local_defines using the make variable $<: local_defines = ['XOC_FILE_ID="$<"]: Bazel aborts telling me that $(<) is not defined
same approach for attribute copts
Of course, I could try to make Bazel call a compiler wrapper script. However, this would mean that I have to explicitly set PATH to my wrapper script(s) before each call to Bazel. Isn't there a better solution?

Answer 1

You have access to {source_file} in a toolchain definition.
This means you have to write your own toolchain definition.
I tried two ways of writing a toolchain:
Use the Bazel tutorial on toolchains. Afterwards my build was broken: The default compile options of Bazel were missing. cc_library did not create shared libraries any more.
Use a hint pointing to a post in bazel-discuss and use the toolchain that Bazel itself creates using your environment. That's what I'm going to describe now (for Bazel 3.5.1)
If you want to use a compiler that is not in $PATH, do bazel clean and update $PATH to make compiler available. Bazel will pick it up.
create a toolchain directory (maybe my-toolchain/) in your workspace
bazel build #bazel_tools//tools/cpp:toolchain
copy BUILD, all *.bzl files, cc_wrapper.sh and builtin_include_directory_paths from $(bazel info output_base)/external/local_config_cc/ to your toolchain directory; copy the files the symbolic links are pointing to instead of copying the symbolic links
Adapt the BUILD file in my-toolchain/ to your needs—like adding '-DXOC_FILE_ID=\\"%{source_file}\\"' to compile_flags of cc_toolchain_config.
add these lines to your .bazelrc to make Bazel use your new toolchain by default:
build:my-toolchain --crosstool_top=//my-toolchain:toolchain
build --config=my-toolchain