dependencies mpi: add -show-compile-info and -show-link-info for mpich

[lgarrison]

Using dependency('mpi') with the MPICH compiler wrappers currently results in compiler warnings about unused command-line arguments. This is because Meson current discovers the compile and link arguments with -compile_info and -link_info:

meson/mesonbuild/dependencies/mpi.py

Lines 112 to 123 in 0ac8ebb

	# --showme for OpenMPI, -compile_info/-link_info for MPICH and IntelMPI
	for comp, link in [('--showme:compile', '--showme:link'), ('-compile_info', '-link_info'), ('-show', None)]:
	try:
	c_args = self.get_config_value([comp], 'compile_args')
	l_args = self.get_config_value([link], 'link_args') if link is not None else c_args
	except DependencyException:
	continue
	else:
	break
	else:
	self.is_found = False
	return

The -compile_info and -link_info flags actually return complete (and identical) compile + link commands, causing link flags to get mixed into Meson's compile command:

❯ mpicc -compile_info
icx -I/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/include -L/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -Wl,-rpath -Wl,/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -lmpi

The newer -show-compile-info instead just shows the compile flags (likewise for -show-link-info):

❯ mpicc -show-compile-info
-I/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/include

Per pmodels/mpich#1045 (specifically pmodels/mpich@f8e9f16), it appears that -show-compile-info and -show-link-info are the preferred ways to get the compile and link flags in recent MPICH/Intel MPI, and that -compile_info and -link_info were kept for legacy reasons.

Summary of command output for completeness

❯ mpicc --version
Intel(R) oneAPI DPC++/C++ Compiler 2025.3.2 (2025.3.2.20260112)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/aurora/26.26.0/oneapi/compiler/2025.3/bin/compiler
Configuration file: /opt/aurora/26.26.0/oneapi/compiler/2025.3/bin/compiler/../icx.cfg

❯ mpicc -compile_info
icx -I/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/include -L/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -Wl,-rpath -Wl,/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -lmpi

❯ mpicc -show-compile-info
-I/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/include

❯ mpicc -link-info        
icx -I/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/include -L/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -Wl,-rpath -Wl,/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -lmpi

❯ mpicc -show-link-info
-L/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -Wl,-rpath -Wl,/opt/aurora/26.26.0/spack/unified/1.1.1/install/linux-x86_64/mpich-5.0.0.aurora_test.3c70a61-hlkigtk/lib -lmpi

With this patch, I confirm that the compile and link arguments are no longer mixed in the Meson build.

[dcbaker]

Did you test this with Intel? I've had #15260 opened for a while because we don't actually query the right tools for the oneAPI based compilers.

[bonzini]

I've had #15260 opened for a while because we don't actually query the right tools for the oneAPI based compilers.

If I understand it correctly, this one is orthogonal to yours (even though they conflict)? Anyway, since you have #15260 I was going to let you merge both in the order that you see fit!

[lgarrison]

I was just using the MPICH wrappers (around the Intel LLVM compilers). A recent-ish Intel OneAPI compiler wrapper (on a different system) doesn't seem to know about -show-compile-info:

❯ which mpicc
/mnt/sw/nix/store/2nwiiy75jgsikpq64yvdgxzjw9iw9xrf-intel-oneapi-mpi-2021.14.2/mpi/2021.14/bin/mpicc

❯ mpicc -show-compile-info
gcc: error: unrecognized command line option ‘-show-compile-info’; did you mean ‘-fno-opt-info’?

But I think that's fine; it just means Meson will continue to discover flags through -compile_info. So I agree that this change should be orthogonal to #15260.