GHC issueshttps://gitlab.haskell.org/ghc/ghc/-/issues2020-07-17T19:06:27Zhttps://gitlab.haskell.org/ghc/ghc/-/issues/17312Potentially unnecessary warning about missing deriving strategies2020-07-17T19:06:27ZtaylorfausakPotentially unnecessary warning about missing deriving strategies## Summary
I'm not sure if this is a bug or not. I ran into it when compiling code using GHC 8.8.1 and `-Weverything`. I was surprised to find that `-Wmissing-deriving-strategies` fires even when there is no ambiguity about which derivi...## Summary
I'm not sure if this is a bug or not. I ran into it when compiling code using GHC 8.8.1 and `-Weverything`. I was surprised to find that `-Wmissing-deriving-strategies` fires even when there is no ambiguity about which deriving strategy should be used. In other words, with no language extensions enabled, (I think) `stock` is the only valid deriving strategy. Therefore I would not expect this warning to fire. I would expect this warning to fire if I had `GeneralizedNewtypeDeriving`, `DeriveAnyClass`, `DerivingStrategies`, or `DerivingVia` enabled.
## Steps to reproduce
``` sh
$ ghc -Wmissing-deriving-strategies -e 'data T = C deriving Eq'
```
```
<interactive>:0:12: warning: [-Wmissing-deriving-strategies]
No deriving strategy specified. Did you want stock, newtype, or anyclass?
Use DerivingStrategies to specify a strategy.
```
## Expected behavior
I expected no warning because the `deriving` clause is not ambiguous.
## Environment
* GHC version used: 8.8.1
Optional:
* Operating System: Windows 10
* System Architecture: x86_648.8.2