Link flag unexpectedly detected as /defaultlib:msvcrt on debug build, expecting /defaultlib:msvcrtd

[Billyzou0741326]

Not sure if this is an issue or if this is expected behavior. Thought that discussion would be a good place to start.

My setup uses [email protected], [email protected] with -DRust_TOOLCHAIN=stable-x86_64-pc-windows-msvc and MSVC 2019 C and CXX compiler.

When I build with Debug config, I'm seeing this link time warning:

(Link target) ->
  LINK : warning LNK4098: defaultlib 'msvcrt' conflicts with use of other libs; use /NODEFAULTLIB:library [C:\Users\ktr\Documents\Projects\c\single001\build\test\c001.vcxproj]

After digging into the build configs generated by -DCMAKE_GENERATOR:STRING=Visual Studio 16 2019 and -DCMAKE_GENERATOR:STRING=Ninja generators respectively, I found the link flags /defaultlib:msvcrt being included:

  // c001.vcxproj
  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
    ...
    <Link>
      <AdditionalDependencies>c001_rust.lib;kernel32.lib;advapi32.lib;ntdll.lib;userenv.lib;ws2_32.lib;kernel32.lib;advapi32.lib;ntdll.lib;userenv.lib;ws2_32.lib;msvcrtd.lib;kernel32.lib;user32.lib;gdi32.lib;winspool.lib;shell32.lib;ole32.lib;oleaut32.lib;uuid.lib;comdlg32.lib;advapi32.lib</AdditionalDependencies>
      ...
      <AdditionalOptions>%(AdditionalOptions) /machine:x64 /defaultlib:msvcrt</AdditionalOptions>

  // build.ninja
  LINK_FLAGS = /machine:x64 /debug /INCREMENTAL /subsystem:console  /defaultlib:msvcrt
  LINK_LIBRARIES = c001_rust.lib  kernel32.lib  advapi32.lib  ntdll.lib  userenv.lib  ws2_32.lib  kernel32.lib  advapi32.lib  ntdll.lib  userenv.lib  ws2_32.lib  msvcrtd.lib  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib

Note the /defaultlib:msvcrt are present in <AdditionalOptions> and LINK_FLAGS. For the sake of testing, I manually changed /defaultlib:msvcrt to /defaultlib:msvcrtd, and the warning went away.

In contrast, msvcrtd.lib are both correctly detected in <AdditioalDependencies> and LINK_LIBRARIES, thanks to the logic here:

corrosion/cmake/FindRust.cmake

Line 192 in 64289b1

list(TRANSFORM libs_list REPLACE "^msvcrt$" "\$<\$<CONFIG:Debug>:msvcrtd>")

where the libs_list correctly substitudes msvcrt with msvcrtd on Debug builds.

However, the flags_list contains /defaultlib:msvcrt, and is not getting substituded:

corrosion/cmake/FindRust.cmake

Lines 181 to 182 in 64289b1

	if (lib MATCHES "^/" AND ${target_triple} MATCHES "msvc$")
	list(APPEND flag_list "${lib}")

Not sure if this is the intended behavior? I think it would make sense to do similar substitutions for the link flags. Though I'm not familiar with cmake scripting at all, something to note would be that /defaultlib:xxx and /DEFAULTLIB:xxx are both valid as link flags are case-insensitive according to msvc docs

[jschwe]

Thanks for the detailed report!

Not sure if this is the intended behavior? I think it would make sense to do similar substitutions for the link flags.

No, that's not intended behavior, we should replace it too. We only need to replace the variant that rustc uses, which is the lowercase /defaultlib:xxx.
This is a quick fix, I can do it later today.

[Billyzou0741326]

I took a stab at this Billyzou0741326@101507b and observed that it builds fine when I point my project to that commit hash.

If that looks acceptable, let me know if I should open a PR (either against master or stable/v0.5, or both?)

[jschwe]

I initially had something similar in mind, but the Generator expression "$<$<CONFIG:Debug>:/defaultlib:msvcrtd>" actually expands to nothing for all configurations except "Debug" (including the most common build configuration "" (empty string). That then lead to #537