rustc always links against non-debug Windows runtime

[jdm]

When building rust-mozjs with debug symbols enabled, the underlying C++ library links against the debug Windows runtime (msvcrtd.lib) rather than the regular one (msvcrt.lib). Unfortunately, rustc always links against msvcrt.lib unconditionally:

rust/src/vendor/libc/src/windows.rs

Line 150 in da2ce22

#[link(name = "msvcrt")]

. This makes it impossible to build a debug-enabled version of rust-mozjs on Windows.

[jdm]

Would there be any objection to doing something like:

#[cfg(all(target_env = "msvc", debug))] // " if " -- appease style checker
#[link(name = "msvcrtd")]
extern {}

#[cfg(all(target_env = "msvc", not(debug_assertions)))] // " if " -- appease style checker
#[link(name = "msvcrt")]
extern {}

cc @retep998

[retep998]

We already have a feature for choosing whether to link the static or dynamic CRT. It would be a fairly trivial matter to add another feature to choose whether to link the debug or release CRT (which I did suggest but nobody seemed to notice). I'd rather not tie this sort of thing to whether optimizations are enabled.

[jdm]

@retep998 says that the way to fix this is to find the relevant bits in #37545 and duplicate it for crt-debug.

[nox]

#37545 landed, what is needed to make some progress on this?

[retep998]

@nox As I said before, someone has to find the relevant bits in #37545 and duplicate it for crt-debug.