crt-static is only translated to `-static` under gcc, not clang

[mqudsi]

In add_default_flags(), the presence of feature crt-static causes -static to be supplied to the compiler iff it's gcc; clang doesn't get the same treatment.

I know that cc itself doesn't compile without -c so the presence of -static makes no difference there, but if a downstream library or crate uses cc to manually get a compiler invocation and runs that without -c to generate an executable itself in build.rs (and some do), it matters.

I can easily open a PR to do the same under clang, but given the subtleties of how much linker-related stuff this crate should be doing to begin with I preferred to first open an issue.

[NobodyXu]

Hmmm, could we remove that -static flag?

I wonder why is that added in the first place.

[mqudsi]

I think removing it makes the most sense. crt-static is not static and shouldn't come with the assumption that just because we're statically linking the runtime it means that all libraries should also be statically linked.

I mean, that's one way of interpreting it but clearly rust doesn't interpret it that way, so we probably shouldn't either.

Not sure about breakage, though.

[NobodyXu]

Not sure about breakage, though.

I think it should be fine.

Don't think there are many crates using cc to generate executables

[NobodyXu]

Looking at it, I found that we also have a function cc::Build::static_flag to add -static.

Honestly I have no idea why it's there in the first place, cc @thomcc Do you know why it is there (and if we could just remove

cc-rs/src/lib.rs

Lines 2173 to 2175 in 3ba2356

	if features.contains("crt-static") {
	cmd.args.push("-static".into());
	}

)?

[mqudsi]

I don't think we can just remove static_flag() itself without breaking a decent amount of code.

It's used a decent amount though as far as I can see it seems most usage is under the very incorrect assumption that it determines whether the output is a .a or .so/.dylib.

Specifically for projects calling .compile(), we should be able to safely remove the flag itself from default_flags() though (and separately mark the static_flag() routine as deprecated).

But a reminder that there are crates that use cc-rs to get build flags before then manually compiling binaries. My own rsconf is only one example; I'm sure there are others.

[NobodyXu]

and separately mark the static_flag() routine as deprecated

I agree, it should be marked as deprecated, while keep the existing implementation.

I will then open a PR to remove

cc-rs/src/lib.rs

Lines 2173 to 2175 in 3ba2356

	if features.contains("crt-static") {
	cmd.args.push("-static".into());
	}

[riidefi]

We should probably specify the clang-equivalent of -MT (on clang-cl) when on Windows. It is odd that if you run SET CXX=clang before cargo build on Windows, the -Ctarget-feature=+crt-static RUSTFLAG is ignored.

E.g.

Tell C++ to use the dynamic version, via one of the following methods (depending on build system):

• Directly specify '/MD' to cl.exe or clang-cl.exe during the C++ compile/link steps.
• Directly specify '-Wl,-nodefaultlib:libcmt -D_DLL -lmsvcrt' to clang++.exe