Conditionally compile only one module at a time

Question

Sometimes while refactoring a change in one of the modules has impact on every other module (or many others), because say a type has been changed or a function parameter has been changed etc. In this case instead of changing everything and then compiling at once is there a way i can compile and run unit tests for only that particular module, tweak it to hearts content and when all is right changed the other modules etc and run the complete/normal cargo build/test ? Of-course one of the ways could be to manually comment/uncomment the module listings in their corresponding root module that introduces them, but is there any other way directly from say cargo test --someflag -only_this_module or something ?

Explaining More:

say I have following modules: a, b, c, d, e, f, g, h where f depends only on g and h but rest of a, b, c, d, e depend on f (and maybe g and h but that should not matter). g and h ofcourse dont depend on anything from above. So if i make a change to f i want to compile only f and test it without changing all of them. Since f depends only on g and h i assume that if things are fine with these three then i should be able to test f even though a, b ... e are broken and crate will not compile if i do the normal cargo build/test . Is this possible.

Answer 1

You can run tests specifically for one module by providing it as an argument to the test binary. Cargo passes arguments to the test binary if you specify it after --, so something like this should work:

cargo test -- module::you::want::to::test

However, you can't compile only a part of a crate. Crates in Rust are units of compilation, like .c files in C, and you can't compile a half of it and ignore the other half.