[MSVC] Rustc is producing inappropriate filetypes w/ `--crate-type=dylib` && `--crate-type=staticlib`.

[DiamondLovesYou]

For example:

/C/msys64/home/Richard/rust-build/x86_64-pc-windows-msvc/stage2/bin/rustc.exe --out-dir /C/msys64/home/Richard/rust-build/x86_64-pc-windows-msvc/test/run-make/output-type-permutations -L /C/msys64/home/Richard/rust-build/x86_64-pc-windows-msvc/test/run-make/output-type-permutations foo.rs --crate-type=staticlib

produces just libbar.a.

 /C/msys64/home/Richard/rust-build/x86_64-pc-windows-msvc/stage2/bin/rustc.exe --out-dir /C/msys64/home/Richard/rust-build/x86_64-pc-windows-msvc/test/run-make/output-type-permutations -L /C/msys64/home/Richard/rust-build/x86_64-pc-windows-msvc/test/run-make/output-type-permutations foo.rs --crate-type=dylib

produces bar.dll, bar.exp, and bar.lib.

Note rlib output works as expected. See output-type-permutations from run-make.

[nagisa]

What’s the issue here? Is the test failing, are the files not accepted by the LINK.EXE or it is simply extensions being not as expected?

.lib may also be an import library without which .dll is pretty much useless. This is probably a reason why dylib emits both .lib and .dll at once. .exp appears to have a similar purpose.

.a should probably be .lib, but then it is ambiguous in case of flag like --crate-type=staticlib,dylib which should produce both and if we try to emit .lib in both cases, we will simply either not emit the static library, or emit an useless dynamic library.

[DiamondLovesYou]

What’s the issue here? Is the test failing, are the files not accepted by the LINK.EXE or it is simply extensions being not as expected?

See #27938 (comment). I don't really know the cause, I use Linux or ssh into a Linux box when I'm on my Surface (my only windows machine) and thus aren't familiar with MSVC's conventions. Whatever the real issue, the test is failing, so I just made the test a no-op on MSVC and filed this issue.

[alexcrichton]

Ok, I've got a branch with this test passing, so I'm going to close this as "working as intended"

[retep998]

The msvc conventions are:

• When building a DLL, emit foo.lib and foo.dll. Downstream code will link to foo.lib and acquire a runtime dependency on foo.dll.
• When building a static library, emit foo.lib. Downstream code will link to foo.lib.
• foo.exp is used when you create foo.lib and foo.dll as two separate steps. foo.exp will be created alongside foo.lib and foo.exp is then passed to the linker to create foo.dll. Beyond that you don't need the foo.exp file.