Cannot specify compiler on command line

[CendioOssman]

Describe the bug
Meson doesn't have a way to override which compiler is used when meson setup is invoked. Unlike $CFLAGS, which has the c_args option, there is no option for $CC. Although meson looks at $CC, that isn't given the highest priority. It breaks in a cross compile where another compiler is specified in the machine configuration.

What's missing is something equivalent to specifying CC=foo as an argument in Autotools.

We need this to override the compiler in automation scripts with a wrapper. Creating temporary configuration files for Meson is just messy there, so we need something that can be dynamically evaluated in just the script.

To Reproduce
meson -D c_compiler=foobar

Expected behavior
The specified compiler overrides any other source that meson has used for the compiler.

system parameters

• Is this a cross build or just a plain native build (for the same computer)?
  Cross
• what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.)
  Custom Linux
• what Python version are you using e.g. 3.8.0
  3.9.20
• what meson --version
  1.7.0
• what ninja --version if it's a Ninja build
  1.12.1

[dcbaker]

Specifically, it sounds to me like the issue you have is that you have a machine file (either a cross file or a native file), it defines a compiler, you want to use a different compiler than that one, and, Meson's priority for for configuration is: cli, machine file, env.

I think this is an actual short coming, and reason to consider adding the command line for meson setup

[dnicolodi]

There is a way to specify a compiler on the command line: just override it with another machine file. Machine files are merged in the order in which they appear in the command line. Maybe it is not the most ergonomic interface, but having "wrong" machine files is not the most common scenario.

[CendioOssman]

I'd like to think this scenario is not that uncommon. The machine file is not that "wrong", in that most of it is perfectly accurate for the target system we're telling meson to build for. It's just one detail in the file we'd like to override.

Specifying another machine file is indeed very not-ergonomic. The automated scripts would need to generate these files as needed (which is made more annoying by the fact that they need to have multiple lines). And we'd need to deal with cleaning up these temporary files as well.

And it of course gets extra annoying that all non-Meson modules are automated one way, and Meson modules need to have a different way.

[CendioOssman]

As a variation of this theme, we could also look at CMake's CMAKE_<LANG>_LINKER_LAUNCHER. This style works for our use case, since we are adding a wrapper for the compiler, rather than completely changing it.

Could this be more fitting? Or perhaps even solvable using some existing mechanism I've failed to find?

[dnicolodi]

Specifying another machine file is indeed very not-ergonomic. The automated scripts would need to generate these files as needed (which is made more annoying by the fact that they need to have multiple lines). And we'd need to deal with cleaning up these temporary files as well.

I don't grok where all the complexity comes from.

mkdir build
cat >build/override <<EOF
[binaries]
cc = ${CC}
EOF
meson setup build --cross-file=something --cross-file=build/override
ninja -C build