Linker args are silently ignored by cargo test

[sgrif]

I've been attempting to run Diesel's test suite on Windows, and can't seem to find a way to link a C library. Specifically what I want to be able to do is cargo test -- -LC:\PostgreSQL\lib, but that argument is silently ignored, as is cargo test -- -C link-args="C:\PostgreSQL\lib". cargo rustc -- -LC:\PostgreSQL\lib works fine (though isn't helpful), but cargo rustc --test -- -LC:\PostgreSQL\lib complains that it doesn't know what -L is, and cargo rustc -- --test -LC:\PostgreSQL\lib doesn't include dev-dependencies.

As such, there appears to be no way to test a crate with cargo on Windows if the crate has C libraries that need to be linked, as there doesn't appear to be an environment variable that can be set either.

[alexcrichton]

Ah, I think that the crux of this issue is a dupe of #2120, so I'm going to close in favor of that, but there's a few other things in play here:

• First, to link a C library, it's generally recommended to use a build script which can do any form of dynamic detection of the OS, runtime, etc. This build script is then generally shipped in the form of a library which is then reusable by everyone!
• cargo test -- -LC:\PostgreSQL\lib - this command is actually saying to pass the -L argument to the test binary which is generated (e.g. the arguments after -- are just passed through). It may be the case that our test binaries just ignore unknown flags (like -L)
• cargo test -- -C link-args="C:\PostgreSQL\lib - as the previous one, this is just passing an argument to the test binary, no the compiler itself.
• cargo rustc -- -LC:\PostgreSQL\lib - this actually will pass the argument to the compiler, but as you've found it wasn't building your test so not too useful.
• cargo rustc --test -- -LC:\PostgreSQL\lib - this is actually an interesting one! So when you pass --test to the cargo rustc command (not the underlying rustc), then you're selecting which test to compile. So what this is actually doing is compiling the test named -- (the first thing after the --test argument). The -L flag is then being interpreted as an argument to cargo rustc itself, which is an unknown flag (hence the error)
• cargo rustc -- --test -LC:\PostgreSQL\lib - aha, and now we run into build test binary with cargo rustc #2120! This should definitely work, but that issue means there's no way for cargo rustc to include dev-dependencies right now unfortunately.