Seems like `optimization=0` does nothing

Describe the bug

It seems that optimization=0 does not have any effect. i.e. -O0 does not appear in the compiling command when using optimization=0.

To Reproduce

With the following code:

// meson.build
project('hello', 'c')
executable('hello', 'hello.c')

// hello.c
#include <stdio.h>
int main(void) {
	puts("Hello world");
	return 0;
}

And using the following commands:

meson setup buildir -Doptimization=0
cd buildir
meson compile -v

I obtain:

ninja: Entering directory `.'
[1/2] gcc -Ihello.p -I. -I.. -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -g -MD -MQ hello.p/hello.c.o -MF hello.p/hello.c.o.d -o hello.p/hello.c.o -c ../hello.c
[2/2] gcc  -o hello hello.p/hello.c.o -Wl,--as-needed -Wl,--no-undefined

Expected behavior

I expected to see -O0 to be passed as an option to GCC.

system parameters

• Is this a cross build or just a plain native build (for the same computer)?: native
• what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.): NixOS
• what Python version are you using e.g. 3.8.0
• what meson --version: 0.57.1
• what ninja --version if it’s a Ninja build: 1.10.2

[eli-schwartz]

Yes, it is the clang default too, which is why the clang mixin returns an empty list too.

The base compiler class emits -O0, it’s only for the compilers which meson knows default to it, that don’t bother to emit this argument in the generated CLI.

[Pamplemousse]

This is only a clang issue, not a GCC one?

Dunno, I haven’t verified it on gcc, but their documentation explicitely say that -O0 is the baseline.

the truth of the matter is that clang doesn’t actually say straight out that -O0 is the default…

Yeah, I looked at the documentation for a little, and the default does not seem to correspond to any of the -O*.