Ways to build transitive dependencies with varying flags?

[gburgessiv]

(I'm semi-new to writing bazel code beyond cc_binary(...); apologies in advance if I confuse terms)

Hey,

I'm trying to figure out how to build the same rust_library with varying rust flags, depending on the needs of the users of the library. Concretely, I'd like to start by offering my users two options when building a rust_binary:

• Optimize all dependencies for size; do not enable LTO of the rust_binary.
• Optimize all dependencies for speed; enable LTO of the rust_binary.

I can make either of these happen for a single bazel build via extra_rustc_flags, and after chatting with folks on the Bazel Slack, it sounds like transitions are likely to be the hammer I want here. I was able to get this to... work with an extra level of indirection and some macro magic.

I was wondering if this is what's roughly expected as the solution to my problem? Am I maybe overcomplicating things/missing a simpler way to go about this? :)

Thanks!