Fix #19649 by using filterInScopeM in rnFamEqn

Previously, associated type family instances would incorrectly claim to
implicitly quantify over type variables bound by the instance head in the
`HsOuterImplicit`s that `rnFamEqn` returned. This is fixed by using
`filterInScopeM` to filter out any type variables that the instance head
binds.

Fixes #19649.

4 files changed, 268 insertions, 20 deletions

diff --git a/compiler/GHC/Rename/HsType.hs b/compiler/GHC/Rename/HsType.hs
index fbdcc15730..d11c4c9634 100644
--- a/compiler/GHC/Rename/HsType.hs
+++ b/compiler/GHC/Rename/HsType.hs
@@ -31,7 +31,7 @@ module GHC.Rename.HsType (
         bindHsOuterTyVarBndrs, bindHsForAllTelescope,
         bindLHsTyVarBndr, bindLHsTyVarBndrs, WarnUnusedForalls(..),
         rnImplicitTvOccs, bindSigTyVarsFV, bindHsQTyVars,
-        FreeKiTyVars,
+        FreeKiTyVars, filterInScopeM,
         extractHsTyRdrTyVars, extractHsTyRdrTyVarsKindVars,
         extractHsTysRdrTyVars, extractRdrKindSigVars,
         extractConDeclGADTDetailsTyVars, extractDataDefnKindVars,
diff --git a/compiler/GHC/Rename/Module.hs b/compiler/GHC/Rename/Module.hs
index d5a787f9ab..8de0c4a34f 100644
--- a/compiler/GHC/Rename/Module.hs
+++ b/compiler/GHC/Rename/Module.hs
@@ -719,7 +719,10 @@ rnFamEqn doc atfi extra_kvars
          -- data instance H :: k -> Type where ...
          --   -- all_imp_vars = [k]
          -- @
-       ; let all_imp_vars = pat_kity_vars ++ extra_kvars
+         --
+         -- For associated type family instances, exclude the type variables
+         -- bound by the instance head with filterInScopeM (#19649).
+       ; all_imp_vars <- filterInScopeM $ pat_kity_vars ++ extra_kvars
 
        ; bindHsOuterTyVarBndrs doc mb_cls all_imp_vars outer_bndrs $ \rn_outer_bndrs ->
     do { (pats', pat_fvs) <- rnLHsTypeArgs (FamPatCtx tycon) pats
@@ -755,8 +758,18 @@ rnFamEqn doc atfi extra_kvars
          -- parent instance declaration is mentioned on the RHS of the
          -- associated family instance but not bound on the LHS, then reject
          -- that type variable as being out of scope.
-         -- See Note [Renaming associated types]
-       ; let lhs_bound_vars = extendNameSetList pat_fvs all_nms
+         -- See Note [Renaming associated types].
+         -- Per that Note, the LHS type variables consist of:
+         --
+         -- * The variables mentioned in the instance's type patterns
+         --   (pat_fvs), and
+         --
+         -- * The variables mentioned in an outermost kind signature on the
+         --   RHS. This is a subset of `rhs_fvs`. To compute it, we look up
+         --   each RdrName in `extra_kvars` to find its corresponding Name in
+         --   the LocalRdrEnv.
+       ; extra_kvar_nms <- mapMaybeM (lookupLocalOccRn_maybe . unLoc) extra_kvars
+       ; let lhs_bound_vars = pat_fvs `extendNameSetList` extra_kvar_nms
              improperly_scoped cls_tkv =
                   cls_tkv `elemNameSet` rhs_fvs
                     -- Mentioned on the RHS...
@@ -1120,7 +1133,7 @@ example:
 Here, we /do/ want to warn that `CF` is unused in the module `C`, as it is
 defined but not used (#18470).
 
-GHC accomplishes this in rnFamInstEqn when determining the set of free
+GHC accomplishes this in rnFamEqn when determining the set of free
 variables to return at the end. If renaming a data family or open type family
 equation, we add the name of the type family constructor to the set of returned
 free variables to ensure that the name is marked as an occurrence. If renaming
diff --git a/testsuite/tests/parser/should_compile/DumpRenamedAst.hs b/testsuite/tests/parser/should_compile/DumpRenamedAst.hs
index a0cb8a36b6..ba136db8e3 100644
--- a/testsuite/tests/parser/should_compile/DumpRenamedAst.hs
+++ b/testsuite/tests/parser/should_compile/DumpRenamedAst.hs
@@ -24,4 +24,11 @@ data T f (a :: k) = MkT (f a)
 type family F1 (a :: k) (f :: k -> Type) :: Type where
   F1 @Peano a f = T @Peano f a
 
+class C a where
+  type F a b
+
+instance C [a] where
+  type F [a] b = Either a b -- Ensure that the HsOuterImplicit for the F
+                            -- instance only quantifies over `b` (#19649)
+
 main = putStrLn "hello"
diff --git a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
index ac53ca8274..f131c08880 100644
--- a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
@@ -13,29 +13,29 @@
         [(L
           (SrcSpanAnn (EpAnn
                        (Anchor
-                        { DumpRenamedAst.hs:27:1-23 }
+                        { DumpRenamedAst.hs:34:1-23 }
                         (UnchangedAnchor))
                        (AnnListItem
                         [])
                        (EpaComments
-                        [])) { DumpRenamedAst.hs:27:1-23 })
+                        [])) { DumpRenamedAst.hs:34:1-23 })
           (FunBind
            {NameSet:
             []}
            (L
-            (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:1-4 })
+            (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:1-4 })
             {Name: DumpRenamedAst.main})
            (MG
             (NoExtField)
             (L
-             (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:1-23 })
+             (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:1-23 })
              [(L
-               (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:1-23 })
+               (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:1-23 })
                (Match
                 (EpAnnNotUsed)
                 (FunRhs
                  (L
-                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:1-4 })
+                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:1-4 })
                   {Name: DumpRenamedAst.main})
                  (Prefix)
                  (NoSrcStrict))
@@ -43,33 +43,33 @@
                 (GRHSs
                  (NoExtField)
                  [(L
-                   { DumpRenamedAst.hs:27:6-23 }
+                   { DumpRenamedAst.hs:34:6-23 }
                    (GRHS
                     (EpAnnNotUsed)
                     []
                     (L
-                     (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:8-23 })
+                     (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:8-23 })
                      (HsApp
                       (EpAnn
                        (Anchor
-                        { DumpRenamedAst.hs:27:8-23 }
+                        { DumpRenamedAst.hs:34:8-23 }
                         (UnchangedAnchor))
                        (NoEpAnns)
                        (EpaComments
                         []))
                       (L
-                       (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:8-15 })
+                       (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:8-15 })
                        (HsVar
                         (NoExtField)
                         (L
-                         (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:8-15 })
+                         (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:8-15 })
                          {Name: System.IO.putStrLn})))
                       (L
-                       (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:17-23 })
+                       (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:34:17-23 })
                        (HsLit
                         (EpAnn
                          (Anchor
-                          { DumpRenamedAst.hs:27:17-23 }
+                          { DumpRenamedAst.hs:34:17-23 }
                           (UnchangedAnchor))
                          (NoEpAnns)
                          (EpaComments
@@ -993,7 +993,233 @@
          (Nothing))))]
      []
      []
-     [])]
+     [])
+   ,(TyClGroup
+     (NoExtField)
+     [(L
+       (SrcSpanAnn (EpAnn
+                    (Anchor
+                     { DumpRenamedAst.hs:(27,1)-(28,12) }
+                     (UnchangedAnchor))
+                    (AnnListItem
+                     [])
+                    (EpaComments
+                     [])) { DumpRenamedAst.hs:(27,1)-(28,12) })
+       (ClassDecl
+        {NameSet:
+         []}
+        (Nothing)
+        (L
+         (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:7 })
+         {Name: DumpRenamedAst.C})
+        (HsQTvs
+         []
+         [(L
+           (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:9 })
+           (UserTyVar
+            (EpAnn
+             (Anchor
+              { DumpRenamedAst.hs:27:9 }
+              (UnchangedAnchor))
+             []
+             (EpaComments
+              []))
+            (())
+            (L
+             (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:27:9 })
+             {Name: a})))])
+        (Prefix)
+        []
+        []
+        {Bag(LocatedA (HsBind Name)):
+         []}
+        [(L
+          (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:28:3-12 })
+          (FamilyDecl
+           (EpAnnNotUsed)
+           (OpenTypeFamily)
+           (NotTopLevel)
+           (L
+            (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:28:8 })
+            {Name: DumpRenamedAst.F})
+           (HsQTvs
+            []
+            [(L
+              (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:28:10 })
+              (UserTyVar
+               (EpAnn
+                (Anchor
+                 { DumpRenamedAst.hs:28:10 }
+                 (UnchangedAnchor))
+                []
+                (EpaComments
+                 []))
+               (())
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:28:10 })
+                {Name: a})))
+            ,(L
+              (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:28:12 })
+              (UserTyVar
+               (EpAnn
+                (Anchor
+                 { DumpRenamedAst.hs:28:12 }
+                 (UnchangedAnchor))
+                []
+                (EpaComments
+                 []))
+               (())
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:28:12 })
+                {Name: b})))])
+           (Prefix)
+           (L
+            { <no location info> }
+            (NoSig
+             (NoExtField)))
+           (Nothing)))]
+        []
+        []))]
+     []
+     []
+     [(L
+       (SrcSpanAnn (EpAnn
+                    (Anchor
+                     { DumpRenamedAst.hs:(30,1)-(31,27) }
+                     (UnchangedAnchor))
+                    (AnnListItem
+                     [])
+                    (EpaComments
+                     [])) { DumpRenamedAst.hs:(30,1)-(31,27) })
+       (ClsInstD
+        (NoExtField)
+        (ClsInstDecl
+         (NoExtField)
+         (L
+          (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:30:10-14 })
+          (HsSig
+           (NoExtField)
+           (HsOuterImplicit
+            [{Name: a}])
+           (L
+            (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:30:10-14 })
+            (HsAppTy
+             (NoExtField)
+             (L
+              (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:30:10 })
+              (HsTyVar
+               (EpAnnNotUsed)
+               (NotPromoted)
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:30:10 })
+                {Name: DumpRenamedAst.C})))
+             (L
+              (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:30:12-14 })
+              (HsListTy
+               (EpAnn
+                (Anchor
+                 { DumpRenamedAst.hs:30:12 }
+                 (UnchangedAnchor))
+                (AnnParen
+                 (AnnParensSquare)
+                 (AR { DumpRenamedAst.hs:30:12 })
+                 (AR { DumpRenamedAst.hs:30:14 }))
+                (EpaComments
+                 []))
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:30:13 })
+                (HsTyVar
+                 (EpAnnNotUsed)
+                 (NotPromoted)
+                 (L
+                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:30:13 })
+                  {Name: a})))))))))
+         {Bag(LocatedA (HsBind Name)):
+          []}
+         []
+         [(L
+           (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:3-27 })
+           (TyFamInstDecl
+            (EpAnn
+             (Anchor
+              { DumpRenamedAst.hs:31:3-27 }
+              (UnchangedAnchor))
+             [(AddEpAnn AnnType (AR { DumpRenamedAst.hs:31:3-6 }))]
+             (EpaComments
+              []))
+            (FamEqn
+             (EpAnnNotUsed)
+             (L
+              (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:8 })
+              {Name: DumpRenamedAst.F})
+             (HsOuterImplicit
+              [{Name: b}])
+             [(HsValArg
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:10-12 })
+                (HsListTy
+                 (EpAnn
+                  (Anchor
+                   { DumpRenamedAst.hs:31:10 }
+                   (UnchangedAnchor))
+                  (AnnParen
+                   (AnnParensSquare)
+                   (AR { DumpRenamedAst.hs:31:10 })
+                   (AR { DumpRenamedAst.hs:31:12 }))
+                  (EpaComments
+                   []))
+                 (L
+                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:11 })
+                  (HsTyVar
+                   (EpAnnNotUsed)
+                   (NotPromoted)
+                   (L
+                    (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:11 })
+                    {Name: a}))))))
+             ,(HsValArg
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:14 })
+                (HsTyVar
+                 (EpAnnNotUsed)
+                 (NotPromoted)
+                 (L
+                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:14 })
+                  {Name: b}))))]
+             (Prefix)
+             (L
+              (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:18-27 })
+              (HsAppTy
+               (NoExtField)
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:18-25 })
+                (HsAppTy
+                 (NoExtField)
+                 (L
+                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:18-23 })
+                  (HsTyVar
+                   (EpAnnNotUsed)
+                   (NotPromoted)
+                   (L
+                    (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:18-23 })
+                    {Name: Data.Either.Either})))
+                 (L
+                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:25 })
+                  (HsTyVar
+                   (EpAnnNotUsed)
+                   (NotPromoted)
+                   (L
+                    (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:25 })
+                    {Name: a})))))
+               (L
+                (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:27 })
+                (HsTyVar
+                 (EpAnnNotUsed)
+                 (NotPromoted)
+                 (L
+                  (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:31:27 })
+                  {Name: b}))))))))]
+         []
+         (Nothing))))])]
    []
    []
    []
@@ -1075,4 +1301,6 @@
               (SrcSpanAnn (EpAnnNotUsed) { DumpRenamedAst.hs:8:19-22 })
               {Name: GHC.Types.Type})))))])))))]
   (Nothing)
-  (Nothing)))
\ No newline at end of file
+  (Nothing)))
+
+