From b55cf28534eaef254c16da050f5e63dc3ff6d7af Mon Sep 17 00:00:00 2001
From: Ryan Scott <ryan.gl.scott@gmail.com>
Date: Mon, 26 Oct 2020 07:18:00 -0400
Subject: [PATCH] tcConArgs: Only typecheck each record type once
---
compiler/GHC/Tc/TyCl.hs | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/compiler/GHC/Tc/TyCl.hs b/compiler/GHC/Tc/TyCl.hs
index eabbe2b4c07a..343a944a1719 100644
--- a/compiler/GHC/Tc/TyCl.hs
+++ b/compiler/GHC/Tc/TyCl.hs
@@ -3413,18 +3413,22 @@ tcConArgs (InfixCon bty1 bty2)
= do { bty1' <- tcConArg bty1
; bty2' <- tcConArg bty2
; return [bty1', bty2'] }
-tcConArgs (RecCon fields)
- = mapM tcConArg btys
+tcConArgs (RecCon (L _ fields))
+ = concatMapM tc_field fields
where
-- We need to ensure that each distinct field name gets its own type.
-- For example, if we have:
--
-- data T = MkT { a,b,c :: Int }
--
- -- Then we should return /three/ Int types, not just one!
- btys = [ hsLinear (cd_fld_type f)
- | L _ f <- unLoc fields
- , _fld_name <- cd_fld_names f ]
+ -- Then we should return /three/ Int types, not just one! At the same
+ -- time, we don't want to kind-check Int three separate times, as that
+ -- would be redundant. Therefore, we kind-check Int once and 'replicate'
+ -- it so that we return three occurrences of it.
+ tc_field :: LConDeclField GhcRn -> TcM [(Scaled TcType, HsSrcBang)]
+ tc_field (L _ f) = do
+ bty' <- tcConArg $ hsLinear $ cd_fld_type f
+ pure $ replicate (length (cd_fld_names f)) bty'
tcConArg :: HsScaled GhcRn (LHsType GhcRn) -> TcM (Scaled TcType, HsSrcBang)
tcConArg (HsScaled w bty)
--
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