add a flag for enabling/suppressing the warning emitted by having both DeriveAnyClass and GeneralizedNewtypeDeriving on.
- rGHC Glasgow Haskell Compiler
Lint Warnings Excuse: It looks ugly if done another way. The crazy long indent also contributes to line length. Severity Location Code Message Warning compiler/typecheck/TcDeriv.hs:1637 TXT3 Line Too Long
No Unit Test Coverage
- Build Status
Buildable 25488 Build 64739: [GHC] Linux/amd64: Continuous Integration Build 64738: [GHC] OSX/amd64: Continuous Integration Build 64737: [GHC] Windows/amd64: Continuous Integration Build 64736: arc lint + arc unit
Make sure to add an entry for this flag in docs/users_guide/using-warnings.rst (see Note [Documenting warning flags]).
Since -Wderiving-defaults is already in standardWarnings, putting it in here is redundant (note that we prepend standardWarnings to the front of this list), so this should be removed.
Currently, this users' guide entry is under the "Compiler" section, but I feel that it might be a better fit in the "Language" section above.
s/New -Wderiving-defaults that/New -Wderiving-defaults flag that/
This is slightly misleading, since enabling GND and DeriveAnyClass simultaneously isn't enough to trigger this warning—you also need to derive an instance of a type class for a newtype (specifically, one for a non-stock class, although we probably don't need to go into that level of detail in the release notes). It might help to give a specific example of some code that would trigger this warning.
s/but not a flag/but not behind a flag/
Surely this test case is going to emit a warning? Make sure to run make accept TEST=T15839a (somewhere in the testsuite directory) to accept the stderr that this produces.