[Git][ghc/ghc][wip/T23153] Show an error when we cannot default a concrete tyvar

[Krzysztof Gogolewski (@monoidal)]

Krzysztof Gogolewski pushed to branch wip/T23153 at Glasgow Haskell Compiler / GHC


Commits:
c318ddb7 by Krzysztof Gogolewski at 2023-03-22T19:58:06+01:00
Show an error when we cannot default a concrete tyvar

Fixes #23153

- - - - -


7 changed files:

- compiler/GHC/Tc/Errors/Ppr.hs
- compiler/GHC/Tc/Errors/Types.hs
- compiler/GHC/Tc/Utils/Zonk.hs
- compiler/GHC/Types/Error/Codes.hs
- + testsuite/tests/rep-poly/T23153.hs
- + testsuite/tests/rep-poly/T23153.stderr
- testsuite/tests/rep-poly/all.T


Changes:

=====================================
compiler/GHC/Tc/Errors/Ppr.hs
=====================================
@@ -1453,6 +1453,11 @@ instance Diagnostic TcRnMessage where
     TcRnTyThingUsedWrong sort thing name
       -> mkSimpleDecorated $
          pprTyThingUsedWrong sort thing name
+    TcRnCannotDefaultConcrete frr
+      -> mkSimpleDecorated $
+         ppr (frr_context frr) $$
+         text "cannot be assigned a fixed runtime representation," <+>
+         text "not even by defaulting."
 
   diagnosticReason = \case
     TcRnUnknownMessage m
@@ -1931,6 +1936,8 @@ instance Diagnostic TcRnMessage where
       -> ErrorWithoutFlag
     TcRnTyThingUsedWrong{}
       -> ErrorWithoutFlag
+    TcRnCannotDefaultConcrete{}
+      -> ErrorWithoutFlag
 
   diagnosticHints = \case
     TcRnUnknownMessage m
@@ -2427,6 +2434,8 @@ instance Diagnostic TcRnMessage where
       -> noHints
     TcRnTyThingUsedWrong{}
       -> noHints
+    TcRnCannotDefaultConcrete{}
+      -> [SuggestAddTypeSignatures UnnamedBinding]
 
   diagnosticCode = constructorCode
 


=====================================
compiler/GHC/Tc/Errors/Types.hs
=====================================
@@ -3257,6 +3257,16 @@ data TcRnMessage where
     -> !Name -- ^ Name of the thing used wrongly.
     -> TcRnMessage
 
+  {- TcRnCannotDefaultConcrete is an error occurring when a concrete
+    type variable cannot be defaulted.
+
+    Test cases:
+      T23153
+  -}
+  TcRnCannotDefaultConcrete
+    :: !FixedRuntimeRepOrigin
+    -> TcRnMessage
+
   deriving Generic
 
 -- | Things forbidden in @type data@ declarations.


=====================================
compiler/GHC/Tc/Utils/Zonk.hs
=====================================
@@ -56,6 +56,7 @@ import GHC.Tc.Utils.TcType
 import GHC.Tc.Utils.TcMType
 import GHC.Tc.Utils.Env   ( tcLookupGlobalOnly )
 import GHC.Tc.Types.Evidence
+import GHC.Tc.Errors.Types
 
 import GHC.Core.TyCo.Ppr     ( pprTyVar )
 import GHC.Core.TyCon
@@ -1810,6 +1811,9 @@ commitFlexi flexi tv zonked_kind
         | isMultiplicityTy zonked_kind
         -> do { traceTc "Defaulting flexi tyvar to Many:" (pprTyVar tv)
               ; return manyDataConTy }
+        | Just (ConcreteFRR origin) <- isConcreteTyVar_maybe tv
+        -> do { addErr $ TcRnCannotDefaultConcrete origin
+              ; return (anyTypeOfKind zonked_kind) }
         | otherwise
         -> do { traceTc "Defaulting flexi tyvar to Any:" (pprTyVar tv)
               ; return (anyTypeOfKind zonked_kind) }


=====================================
compiler/GHC/Types/Error/Codes.hs
=====================================
@@ -539,6 +539,7 @@ type family GhcDiagnosticCode c = n | n -> c where
   GhcDiagnosticCode "TcRnBadlyStaged"                               = 28914
   GhcDiagnosticCode "TcRnStageRestriction"                          = 18157
   GhcDiagnosticCode "TcRnTyThingUsedWrong"                          = 10969
+  GhcDiagnosticCode "TcRnCannotDefaultConcrete"                     = 52083
 
   -- IllegalNewtypeReason
   GhcDiagnosticCode "DoesNotHaveSingleField"                        = 23517


=====================================
testsuite/tests/rep-poly/T23153.hs
=====================================
@@ -0,0 +1,8 @@
+module T23153 where
+
+import GHC.Exts
+
+f :: forall r s (a :: TYPE (r s)). a -> ()
+f = f
+
+g h = f (h ())


=====================================
testsuite/tests/rep-poly/T23153.stderr
=====================================
@@ -0,0 +1,15 @@
+
+T23153.hs:8:1: error: [GHC-52083]
+    The argument ‘(h ())’ of ‘f’
+    cannot be assigned a fixed runtime representation, not even by defaulting.
+    Suggested fix: Add a type signature.
+
+T23153.hs:8:1: error: [GHC-52083]
+    The argument ‘(h ())’ of ‘f’
+    cannot be assigned a fixed runtime representation, not even by defaulting.
+    Suggested fix: Add a type signature.
+
+T23153.hs:8:1: error: [GHC-52083]
+    The argument ‘(h ())’ of ‘f’
+    cannot be assigned a fixed runtime representation, not even by defaulting.
+    Suggested fix: Add a type signature.


=====================================
testsuite/tests/rep-poly/all.T
=====================================
@@ -116,3 +116,4 @@ test('T21650_b', normal, compile_fail, ['-Wno-deprecated-flags'])            ##
 
 
 test('T23051', normal, compile_fail, [''])
+test('T23153', normal, compile_fail, [''])



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/c318ddb78ff7276c5721f26a530116ccd370be72

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/c318ddb78ff7276c5721f26a530116ccd370be72
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