#3449: Unavoidable "unused bindings" warnings in boot files
-----------------------------+----------------------------------------------
Reporter: heatsink | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.10.4 | Severity: minor
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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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.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3449>
GHC <http://www.haskell.org/ghc/>
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