defmt-test: #[cfg(test)] the #[defmt_test::tests] module

[japaric]

it recently came to my attention that one can use defmt-test for "unit testing" by using it in src/lib.rs (although this is pretty limited at the moment because one can only use the defmt_test::tests once in a library crate)

if one does use defmt_test like that then they may run into the issue that running the test files in tests fails with this cryptic linker message:

  = note: rust-lld: error: duplicate symbol: main

the issue is that the code generated by defmt_test::tests (which includes a function with unmangled name main) is not conditionally compiled but we do want that to be #[cfg(test)]-ed because it contains test code.

r? @jonas-schievink

[japaric]

argh, our defmt-test snapshot test is unusual because is a bin/*.rs file and not a proper test/*.rs file which does get compiled with --cfg test when you do cargo test. this will require xtask changes to land. turning into a draft PR for now

[Urhengulas]

Looks good to me. firmware/qemu/tests/defmt-test.out.new and firmware/qemu/tests/defmt-test.release.out.new probably should be removed?

[japaric]

Looks good to me. firmware/qemu/tests/defmt-test.out.new and firmware/qemu/tests/defmt-test.release.out.new probably should be removed?

good catch! done and added a gitignore to prevent that in the future

bors r=Urhengulas

[bors]

Build succeeded:

• ci