Unavoidable "unused bindings" warnings in boot files

The -fwarn-unused-binds flag produces warnings for bindings that cannot, in fact, be deleted from hs-boot files. It would be nice not to see these warnings. Definitions in .hs-boot files must match the definitions in .hs files, but .hs-boot files don't necessarily use or export the same identifiers that the .hs file does.

Running ghc -c A.hs-boot -fwarn-unused-binds produces warnings for this hs-boot file, regardless of whether the identifiers are exported in the hs file.

{- A.hs-boot -}
{-# OPTIONS_GHC -XTypeFamilies #-} -- to demonstrate associated type warnings
module A(Foo, HasFoo) where

newtype Foo = Foo {unFoo :: Int}
class HasFoo a where
  data Foo' a
  getFoo :: a -> Foo

For identifiers defined on the RHS of an equal sign or 'where'---namely, data constructors, field names, class methods, and associated types---I suggest silencing unused binding warnings in the boot file. The rationale is that you should be allowed to copy an entire definition into the boot file, and regard a binding as unused only if it appears unused in the .hs file.

See also #3283.

Trac metadata

Trac field	Value
Version	6.10.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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