Document compiler warning_level project option

[ptomato]

Searching for it in the documentation turns up nothing. It cost me quite a lot of source-diving to find out whether 1 or 3 was the most strict warning level.

[mwleeds]

I think this can be closed? The documentation is here: https://mesonbuild.com/Builtin-options.html#

[ptomato]

Excellent, thanks!

[le-jzr]

So, what do those levels actually mean? 3 being "the most strict" doesn't really say much, when I don't know which warnings are enabled. That would have been fine in the past, but with current version, meson actually spews warnings about "please use this vague option instead of manually using -Wall -Wextra", and I find that risky when it's not even documented what it's meant to mean exactly.

[philippludwig]

I agree about that. I have read the GCC manpage and have a pretty exact idea which warnings I would like to enable.

Furthermore, there should be an easy copy&paste snippet on the documentation page. If I write warning_level(3), I get:

meson.build:2:0: ERROR: Unknown function "warning_level".

And I don’t find any indication on how this option is being used correctly.

Therefore, I would like to suggest that the warning WARNING: Consider using the builtin warning_level option instead of adding warning flags by hand. is removed.

I assume that this feature is intended as some compiler-agnostic warning setting, but when I don’t care about other compilers, just let me set my flags as I would like without printing something like this.

[eli-schwartz]

Worse is the fact that:

• warning_level 1 adds -Wall,
  -warning_level 2 adds warning_level 1 + -Wextra,
• warning_level 3 adds warning_level 2 + -Wpedantic

But some projects want -Wall and -Wpedantic, but refuse to add -Wextra because it's not a stable definition. It's therefore impossible to use the meson option. So the warning is useless, as it will warn you about things you cannot change.

[smac89]

Worse is the fact that:

* warning_level 1 adds `-Wall`,
  -warning_level 2 adds warning_level 1 + `-Wextra`,

* warning_level 3 adds warning_level 2 + `-Wpedantic`

But some projects want -Wall and -Wpedantic, but refuse to add -Wextra because it's not a stable definition. It's therefore impossible to use the meson option. So the warning is useless, as it will warn you about things you cannot change.

It would be nice if the above was documented to include the corresponding warning flags for different languages

[eli-schwartz]

I submitted #7973 to stop meson from reprimanding you if you manually add -Wpedantic, did not (currently) try to document the flags each level add though.

[shemminger]

What about -Werror?

[eli-schwartz]

meson.build:11: WARNING: Consider using the built-in werror option instead of using "-Werror".

Given there is a dedicated option just for Werror, I think it's perfectly reasonable that people should use that built-in option. There is no case where using it would also have the side effect of adding things you don't want to add, like there was with -Wpedantic.

[zippy2]

Given there is a dedicated option just for Werror, I think it's perfectly reasonable that people should use that built-in option.

I beg to differ. There are projects which want to turn on -Werror when building from a git repo (i.e. when .git dir exists) but not when building from a release tarball as the latter maybe run on plethora of systems unavailable to developers and thus may fail build needlessly.

If we want projects to use builtin we need to give them an opportunity to set it outside of project().

[eli-schwartz]

That will fail the build needlessly when users build from a git checkout.

[zippy2]

Which is acceptable, because that's usually the case for advanced users building their own package (and they probably know ho to report this back to the project in question). Majority of users use distro shipped binary packages -> no problem.

[eli-schwartz]

• It's nowhere near true to say that only advanced users build from git checkouts.
• Even advanced users cannot use their advanced knowledge to report the bug and then, having done their "duty", build the software anyway and ignore the warning. There's no option to disable -Werror hardcoded in the build files.
• Claiming the majority of users use distro shipped binary packages implies that distros actually ship all software as binary packages, but they don't. They ship lots of popular software, and some unpopular software, but there is always stuff that users need to build themselves in order to use it. This ties back into point 1.

[Consolatis]

• warning_level 1 adds -Wall,
• warning_level 2 adds warning_level 1 + -Wextra,
• warning_level 3 adds warning_level 2 + -Wpedantic

Is this documented somewhere?
https://mesonbuild.com/Builtin-options.html only states From 0 = none to everything = highest.

On a side note: It seems neither none nor everything are the correct definitions of what that setting actually does.

[xclaesse]

Maybe we should deprecate numerical values, and have more proper names. Like -Dwarning_level=all,pedantic. Probably would require some approximative mapping for compilers other than gcc/clang.