On Windows: Linking against standard libraries

[Helcaraxan]

For C++, linkopts allows one to specify linker options. However, it also states that:

Each element of this list that does not start with $ or - is assumed to be the label of a target in deps. The list of files generated by that target is appended to the linker options. An error is reported if the label is invalid, or is not declared in deps.

As far as I can see, this means that I cannot specify plain arguments to the linker, e.g. User32.lib, as required for some system libraries.

I got it to link to the system library by copying it locally, specifying it as a srcs in a cc_library, and referring to the library's label in both deps and linkopts. However, copying a system library seems like a bad idea. The C++ system header files are already picked up automatically by Bazel, so maybe these libraries should be, too. I noticed that CMake automatically links against some libraries on Windows, i.e. it links against user32.lib advapi32.lib gdi32.lib when compiling openssl on Windows without explicitly specifying these anywhere.

[hermione521]

@meteorcloudy

[laszlocsomor]

You can use linkopts = ["-Wl,user32.lib", "-Wl,advapi32.lib"].

$ cat foo/BUILD
cc_binary(
    name = 'foo',
    srcs = ['foo.cc'],
    linkopts = ['-Wl,user32.lib'],
)

$ cat foo/foo.cc
#include <Windows.h>

int main(int, char**) {
  MessageBoxA(0, "text", "caption", 0);
  return 0;
}

$ bazel run --cpu=x64_windows_msvc //foo
...
INFO: Running command line: C:/tools/msys64/var/tmp/Bazel/MGAgSgPx/execroot/bazel2/bazel-out/vc_14_0_x64-fastbuild/bin/foo/foo.exe

See the command line translation here:

bazel/tools/cpp/wrapper/bin/pydir/msvc_link.py

Line 40 in 088bbc6

(r'-Wl,(.+)\.lib', ['$0.lib']),

---

From Bazel 0.5.3, we no longer use wrapper script to invoke MSVC compiler anymore. So -Wl,<lib> won't be translated, please use -DEFAULTLIB:<lib> instead.

[Helcaraxan]

Thanks for the solution!

[grandseiken]

Thanks laszlo! You walked out that elevator like a boss!

[laszlocsomor]

@grandseiken : hey Stuart, small world :)