diff options
Diffstat (limited to 'compiler/typecheck/TcInstDcls.hs')
| -rw-r--r-- | compiler/typecheck/TcInstDcls.hs | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/compiler/typecheck/TcInstDcls.hs b/compiler/typecheck/TcInstDcls.hs index dbc818b140..8d8d23dd77 100644 --- a/compiler/typecheck/TcInstDcls.hs +++ b/compiler/typecheck/TcInstDcls.hs @@ -46,7 +46,8 @@ import Class import Var import VarEnv import VarSet -import PrelNames ( typeableClassName, genericClassNames ) +import PrelNames ( typeableClassName, genericClassNames + , knownNatClassName, knownSymbolClassName ) import Bag import BasicTypes import DynFlags @@ -518,9 +519,10 @@ doClsInstErrorChecks inst_info -- In hs-boot files there should be no bindings ; failIfTc (is_boot && not no_binds) badBootDeclErr - -- Handwritten instances of the poly-kinded Typeable - -- class are always forbidden - ; failIfTc (clas_nm == typeableClassName) typeable_err + -- Handwritten instances of any rejected + -- class is always forbidden + -- #12837 + ; failIfTc (clas_nm `elem` rejectedClassNames) clas_err -- Check for hand-written Generic instances (disallowed in Safe Haskell) ; when (clas_nm `elem` genericClassNames) $ @@ -538,11 +540,14 @@ doClsInstErrorChecks inst_info text "Replace the following instance:") 2 (pprInstanceHdr ispec) - -- Report an error or a warning for a Typeable instances. + -- Report an error or a warning for certain class instances. -- If we are working on an .hs-boot file, we just report a warning, -- and ignore the instance. We do this, to give users a chance to fix -- their code. - typeable_err = text "Class" <+> quotes (ppr clas_nm) + rejectedClassNames = [ typeableClassName + , knownNatClassName + , knownSymbolClassName ] + clas_err = text "Class" <+> quotes (ppr clas_nm) <+> text "does not support user-specified instances" {- |