Multiple c_std values fail

[vid512]

Describe the bug

When building project using multiple c_std value with clang-cl, the resulting compiler option is invalid.

To Reproduce

create empty file testma.cpp

create: meson.build:

project('testma', 'cpp', default_options: ['cpp_std=c++latest'])
miniaudio = dependency('miniaudio')
executable('testma', ['testma.cpp'], dependencies: [miniaudio])

In Visual Studio developer environment with clang, do:

mkdir subprojects
meson wrap install miniaudio
set CC=clang-cl
set CXX=clang-cl
meson setup build

The resulting build/build.ninja contains invalid options "/clang:-std=gnu11,c11,gnu99,c99,gnu89,c89". For example:

build subprojects/miniaudio-0.11.22/extras/nodes/libma_channel_combiner_node.a.p/ma_channel_combiner_node_ma_channel_combiner_node.c.obj: c_COMPILER ../subprojects/miniaudio-0.11.22/extras/nodes/ma_channel_combiner_node/ma_channel_combiner_node.c
 DEPFILE = "subprojects\miniaudio-0.11.22\extras\nodes\libma_channel_combiner_node.a.p\ma_channel_combiner_node_ma_channel_combiner_node.c.obj.d"
 DEPFILE_UNQUOTED = subprojects\miniaudio-0.11.22\extras\nodes\libma_channel_combiner_node.a.p\ma_channel_combiner_node_ma_channel_combiner_node.c.obj.d
 ARGS = "-Isubprojects\miniaudio-0.11.22\extras\nodes\libma_channel_combiner_node.a.p" "-Isubprojects\miniaudio-0.11.22" "-I..\subprojects\miniaudio-0.11.22" "/MDd" "/nologo" "/showIncludes" "/utf-8" "/W4" "/clang:-std=gnu11,c11,gnu99,c99,gnu89,c89" "/Od" "/Zi" "/Fdsubprojects\miniaudio-0.11.22\extras\nodes\libma_channel_combiner_node.a.p\ma_channel_combiner_node_ma_channel_combiner_node.c.pdb"

Note that the subprojects\miniaudio-0.11.22\meson.build contains:

project(
...
  default_options: [
    ...
    'c_std=gnu11,c11,gnu99,c99,gnu89,c89',
  ],
)

Expected behavior

Meson selects only one C standard, and produces valid clang-cl command in build.ninja.

system parameters

• Windows 11 64-bit
• Native build
• python 3.13.1
• meson 1.9.1
• miniaudio-0.11.22
• clang-cl 18.1.8
• ninja 1.12.1

[WillAyd]

I don't think this is clang specific as I've hit the same issue with gcc

[dcbaker]

@WillAyd Was that on Windows with GCC? (Trying to triage a bit on how to reproduce)

[WillAyd]

I encountered this submitting a package to the wrapdb - you can see the failing CI run here on Ubuntu:

https://github.com/mesonbuild/wrapdb/actions/runs/18540619934/job/52846868827?pr=2449#step:6:88291

I didn't dive too deeply, but my hunch is that this has to do with how this value is parsed from subprojects

[vid512]

I can reproduce this on Linux with GCC. Follow exactly the same steps, just replace c++latest withc++23 in meson.build, and don't set CC or CXX. Tested with meson 1.9.1.

Eg. meson.build:

project('testma', 'cpp', default_options: ['cpp_std=c++23'])
miniaudio = dependency('miniaudio')
executable('testma', ['testma.cpp'], dependencies: [miniaudio])

Commands:

mkdir subprojects
meson wrap install miniaudio
meson setup build

Resulting build.ninja contains:

build subprojects/miniaudio-0.11.22/extras/nodes/libma_channel_combiner_node.a.p/ma_channel_combiner_node_ma_channel_combiner_node.c.o: c_COMPILER ../subprojects/miniaudio-0.11.22/extras/nodes/ma_channel_combiner_node/ma_channel_combiner_node.c
 DEPFILE = subprojects/miniaudio-0.11.22/extras/nodes/libma_channel_combiner_node.a.p/ma_channel_combiner_node_ma_channel_combiner_node.c.o.d
 DEPFILE_UNQUOTED = subprojects/miniaudio-0.11.22/extras/nodes/libma_channel_combiner_node.a.p/ma_channel_combiner_node_ma_channel_combiner_node.c.o.d
 ARGS = -Isubprojects/miniaudio-0.11.22/extras/nodes/libma_channel_combiner_node.a.p -Isubprojects/miniaudio-0.11.22 -I../subprojects/miniaudio-0.11.22 -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -std=gnu11,c11,gnu99,c99,gnu89,c89 -O0 -g -fPIC -pthread

[vid512]

Also note that with MSVC, the resulting build command doesn't contain /std:c11 (which is the only option valid for MSVC out of the list), or any other /std option. I would also consider this a minor bug. The default for MSVC is not c11, but rather it's own non-conforming c89-like mode. See https://learn.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=msvc-170

The default C compiler (that is, the compiler when /std:c11 or /std:c17 isn't specified) implements ANSI C89, but includes several Microsoft extensions, some of which are part of ISO C99.

[bgilbert]

Smaller reproducer, on Fedora 43 with GCC:

• meson.build:

project('a', 'cpp')
subproject('foo')

• subprojects/foo/meson.build:

project('foo', 'c', default_options: ['c_std=gnu11,c11'])
library('foo', 'foo.c')

• subprojects/foo/foo.c: empty file.

Build log:

[1/2] Compiling C object subprojects/foo/libfoo.so.p/foo.c.o
FAILED: [code=1] subprojects/foo/libfoo.so.p/foo.c.o 
cc -Isubprojects/foo/libfoo.so.p -Isubprojects/foo -I../subprojects/foo -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -std=gnu11,c11 -O0 -g -fPIC -MD -MQ subprojects/foo/libfoo.so.p/foo.c.o -MF subprojects/foo/libfoo.so.p/foo.c.o.d -o subprojects/foo/libfoo.so.p/foo.c.o -c ../subprojects/foo/foo.c
cc: error: unrecognized command-line option ‘-std=gnu11,c11’; did you mean ‘-std=gnu++11’?
ninja: build stopped: subcommand failed.

If the main project has project('a', 'c') instead of project('a', 'cpp'), the problem does not occur.

This was introduced in 1.9.1 by a747c4e. In the master branch, it was introduced by 85f16a1 and subsequently fixed by c0a5e92.

cc @bonzini

[bgilbert]

Putting project('a', 'c', 'cpp') in the root project also fixes the problem, so the issue occurs when a subproject uses a language the superproject doesn't.

[bonzini]

#15062 is already in the 1.9.2 milestone.