Print which warning-flag controls/enabled an emitted warning
Both gcc
and clang
tell which warning flag a reported warning can be controlled with, e.g.
$ clang-3.5 -Wall -c hello.c
hello.c:3:7: warning: unused variable 'x' [-Wunused-variable]
int x;
^
1 warning generated.
$ gcc -Wall -c hello.c
hello.c: In function ‘main’:
hello.c:3:7: warning: unused variable ‘x’ [-Wunused-variable]
int x;
^
hello.c:4:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^
With GHC however, we need to lookup the documentation (or memorise all warning flags) to find out which -fno-warn-*
flag we need to use to silence a specific warning.
I propose we augment GHC's warnings in a similar style to how gcc
/clang
report flags in compile warnings.
As an obvious extension, (which maybe should be controlled by some -f
flag, e.g. -f(no-)show-warning-groups
), GHC could then also show by which warning-group a given warning is implied, e.g.
WCompatWarningsOn.hs:16:1: warning: [-Wsemigroup (in -Wcompat)]
Local definition of ‘<>’ clashes with a future Prelude name.
This will become an error in a future release.
WCompatWarningsOn.hs:22:3: warning: [-Wnoncanonical-monoid-instances (in -Wcompat)]
Noncanonical ‘(<>) = mappend’ definition detected
in the instance declaration for ‘Semi.Semigroup S’.
Move definition from ‘mappend’ to ‘(<>)’
For the warning-sets which form a superset chain (Weverything > Wextra > Wall > Wdefault) we'd only mention the smallest one (and omit the trivial -Weverything
set altogether) to keep the output concise.