From c4a2c5f6034b26425f617844b158457a592be379 Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Wed, 2 Jan 2013 16:24:14 +0000
Subject: [PATCH] Tidy the type in badInstSigErr (fixes Trac #7545)
---
compiler/typecheck/TcInstDcls.lhs | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs
index e9a49cec5e24..00d1d26495f9 100644
--- a/compiler/typecheck/TcInstDcls.lhs
+++ b/compiler/typecheck/TcInstDcls.lhs
@@ -874,16 +874,24 @@ mkMethIds sig_fn clas tyvars dfun_ev_vars inst_tys sel_id
do { sig_ty <- tcHsSigType (FunSigCtxt sel_name) hs_ty
; inst_sigs <- xoptM Opt_InstanceSigs
; if inst_sigs then
- checkTc (sig_ty `eqType` local_meth_ty)
- (badInstSigErr sel_name local_meth_ty)
+ unless (sig_ty `eqType` local_meth_ty)
+ (badInstSigErr sel_name local_meth_ty)
else
addErrTc (misplacedInstSig sel_name hs_ty)
; return sig_ty }
-badInstSigErr :: Name -> Type -> SDoc
+badInstSigErr :: Name -> Type -> TcM ()
badInstSigErr meth ty
- = hang (ptext (sLit "Method signature does not match class; it should be"))
- 2 (pprPrefixName meth <+> dcolon <+> ppr ty)
+ = do { env0 <- tcInitTidyEnv
+ ; let tidy_ty = tidyType env0 ty
+ -- Tidy the type using the ambient TidyEnv,
+ -- to avoid apparent name capture (Trac #7475)
+ -- class C a where { op :: a -> b }
+ -- instance C (a->b) where
+ -- op :: forall x. x
+ -- op = ...blah...
+ ; addErrTc (hang (ptext (sLit "Method signature does not match class; it should be"))
+ 2 (pprPrefixName meth <+> dcolon <+> ppr tidy_ty)) }
misplacedInstSig :: Name -> LHsType Name -> SDoc
misplacedInstSig name hs_ty
--
GitLab