Feature request: Configurable warnings

[langston-barrett]

Lots of compilers have a lot of configurability around the warnings they emit. A classic example would be gcc or clang, which have a number of great features:

• Every warning has an individual toggle (the -W flags)
• There are groups of warnings that can be mass-enabled depending on your level of pedantry (-Wall should basically always be used, -Wpedantic for the extra careful)
• Warnings can be made into errors via a flag (-Werror), either individually or collectively.

It'd be great to get some of these features in Souffle!

[mmcgr]

There are some existing options when running souffle-compile that may help. souffle-compile -t adds -g -O0 -Wall -Wextra -Werror to the compilation flags. souffle-compile -w adds -Wall -Wextra to the compilation flags. CXXFLAGS="[your own custom settings]" souffle-compile will prepend your own flags.

These do require you to run souffle -g[name].cpp, then compile with souffle-compile [name].cpp instead of just souffle -c

[langston-barrett]

I was thinking about warnings from Souffle itself, just using C compilers as an example (though it's good to know about those options to souffle-compile as well). I think it would be useful to (selectively) make warnings such as these into errors (for example, in CI).

Warning: Variable Config only occurs once in ./signatures.dl:185:40
Warning: No rules/facts defined for relation debuginfo_is_loaded in file entry.dl at line 2
.decl debuginfo_is_loaded()

[langston-barrett]

Copying from #2319, the remaining steps for this feature are:

• Turning specific/all warnings into errors (and demoting specific warnings from errors back into warnings).
• Discoverability of warning flags (optimally via the CLI).
• Allow warnings to default to "off".
• Document flag behavior; currently "no" trumps "yes".
• Make a .suppress-warning pragma, like .suppress-warnings except that it takes the name of a specific warning to suppress, and optimally can be specified multiple times (for different relations).