0.50 regression: Default option c_std not applied when cross-compiling

[lgrahl]

When providing default_options: ['c_std=c99'] to the project, it is not being applied on meson build --cross-file <cross-file> invocation on a simple test project using flexible array members:

ninja -v

[1/2] cc -Itest-executable@exe -I. -I../../work -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -g -pedantic -MD -MQ 'test-executable@exe/main.c.o' -MF 'test-executable@exe/main.c.o.d' -o 'test-executable@exe/main.c.o' -c ../../work/main.c
../../work/main.c:5:9: warning: ISO C90 does not support flexible array members [-Wpedantic]
int array[];
^
[2/2] cc -o test-executable 'test-executable@exe/main.c.o' -Wl,--no-undefined -Wl,--as-needed

However, after doing any kind of (even unrelated) configuration such as meson configure -Db_asneeded=true, the configuration is being fixed and applies as expected:

ninja -v

[1/2] cc -Itest-executable@exe -I. -I../../work -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -std=c99 -g -pedantic -MD -MQ 'test-executable@exe/main.c.o' -MF 'test-executable@exe/main.c.o.d' -o 'test-executable@exe/main.c.o' -c ../../work/main.c
[2/2] cc -o test-executable 'test-executable@exe/main.c.o' -Wl,--no-undefined -Wl,--as-needed

Note: I haven't tested whether this also applies to other default options.

---

main.c

#include <stdio.h>

struct a {
    int foo;
    int array[];
};

int main(int argc, char* argv[]) {
    printf("Hey!\n");
    return 0;
}

meson.build

project('test-project', 'c', version: '0.0.1', default_options: ['c_std=c99'])
add_project_arguments('-pedantic', language: 'c')
executable('test-executable', 'main.c')

cross-file

[host_machine]
system = 'linux'
cpu_family = 'x86_64'
cpu = 'x86_64'
endian = 'little'

[properties]
root = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64'
needs_exe_wrapper = true

[paths]
prefix = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/sysroot'

[binaries]
c = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/x86_64-linux-android28-clang'
cpp = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/x86_64-linux-android28-clang++'
ar = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/x86_64-linux-android-ar'
as = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/x86_64-linux-android-as'
ld = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/ld.lld'
strip = '/usr/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/x86_64-linux-android-strip'
pkgconfig = '/usr/bin/pkg-config'

[lgrahl]

What's also weird is that it's trying to use native cc to compile instead of using the cross-compiler. I've opened a new issue for that (#5102). However, the above described issue also happens when cross-compiling for ARM (using the appropriate cross-compiler).

[mgautierfr]

I have the same issue. (with cpp_std).
This is a regression with 0.50.0. 0.49.2 correctly pass the option (-std=c++11 in my case) to the compiler.

It seems also that meson doesn't append LDFLAGS and CPPFLAGS from environment for c and cpp compiler. (Also a regression, 0.49.2 works)

[lgrahl]

I can also confirm that it works with 0.49.2.

[michaelolbrich]

I'm seeing the same thing here. The fist broken commit is 19f81d3.

[nirbheek]

CCing @Ericson2314

[Ericson2314]

Hmm so this option affected native and cross compilation previously? That is fine, but inconsistent with the other options. I'll take a look.

[michaelolbrich]

I'm not sure what you think should happen but systemd, mesa and libdrm set c_std in the default_options and with the current meson release the all fail to cross-compile with a compiler that uses an older standard by default.

[Ericson2314]

@michaelolbrich for comparison what does c_args or c_link_args do in default_options, and what do all 3 do as -D cli args to meson?

(I'm in transit so can't check yet. Not just asking rhetorically :). )

[michaelolbrich]

As soon as I use --cross-file, c_args c_link_args and c_std are all ignored. For default_options and as -D cli args.

[Ericson2314]

@michaelolbrich Thanks! That is the new behavior?

[michaelolbrich]

For c_std that's new. For c_args and c_link_args this was also the case in 0.49.0.

I'm not sure what c_args is supposed to be used for but the correct C standard depends on the code that is compiled. Cross-compiling or not should not have an effect for this.

And after doing some testing, I must say that it is very confusing that command line options don't have any effect.

[Ericson2314]

Yes it is confusing. So the regession was due to me trying to match the status quo in a pure refactor, but not realizing c_std worked differently. What I actually want is #4963. This would solve your issue completely in that default_options works reliably whether or not the user is cross or native compiling.

[Ericson2314]

Could somebody assign this to me too?

[jpakkane]

I debugged why this happens. In get_compiler_options_for_target an OverrideProxy is created and it overrides c_std to be none. It should not do that since c_std is not a per-machine setting. It should be the same for native and cross compilation (at least for now to preserve backwards compatibility).

Maybe once we get cross_c_args et al we could also have a cross_c_std, but I'm not sure even that is necessary.

[Ericson2314]

@jpakkane So right now all compiler options are per-machine, since compilers target a single machine (as far as meson knows). The solution I think is when reading in the file to make a temporary hack to duplicate this one.

Maybe once we get cross_c_args et al we could also have a cross_c_std, but I'm not sure even that is necessary.

I have done GCC native, Clang cross builds where the clang might support a newer standard.