Suggest similar names when reporting types in terms (#19978)wip/suggest-term-names

This fixes an error message regression.

5 files changed, 83 insertions, 27 deletions

diff --git a/compiler/GHC/Tc/Gen/Head.hs b/compiler/GHC/Tc/Gen/Head.hs
index f71b424ffa..0e90a22862 100644
--- a/compiler/GHC/Tc/Gen/Head.hs
+++ b/compiler/GHC/Tc/Gen/Head.hs
@@ -44,6 +44,8 @@ import GHC.Tc.Instance.Family ( tcLookupDataFamInst )
 import GHC.Core.FamInstEnv    ( FamInstEnvs )
 import GHC.Core.UsageEnv      ( unitUE )
 import GHC.Rename.Utils       ( unknownSubordinateErr )
+import GHC.Rename.Unbound     ( unknownNameSuggestions, WhatLooking(..) )
+import GHC.Unit.Module        ( getModule )
 import GHC.Tc.Errors.Types
 import GHC.Tc.Solver          ( InferMode(..), simplifyInfer )
 import GHC.Tc.Utils.Env
@@ -702,46 +704,52 @@ tc_infer_assert assert_name
 tc_infer_id :: Name -> TcM (HsExpr GhcTc, TcSigmaType)
 tc_infer_id id_name
  = do { thing <- tcLookup id_name
-      ; global_env <- getGlobalRdrEnv
       ; case thing of
              ATcId { tct_id = id }
                -> do { check_local_id id
                      ; return_id id }
 
-             AGlobal (AnId id)
-               -> return_id id
+             AGlobal (AnId id) -> return_id id
                -- A global cannot possibly be ill-staged
                -- nor does it need the 'lifting' treatment
                -- Hence no checkTh stuff here
 
-             AGlobal (AConLike cl) -> case cl of
-                 RealDataCon con -> tcInferDataCon con
-                 PatSynCon ps    -> tcInferPatSyn id_name ps
-
-             AGlobal (ATyCon ty_con)
-               -> fail_tycon global_env ty_con
-
-             ATyVar name _
-                -> failWithTc $
-                     text "Illegal term-level use of the type variable"
-                       <+> quotes (ppr name)
-                       $$ nest 2 (text "bound at" <+> ppr (getSrcLoc name))
-
-             ATcTyCon ty_con
-               -> fail_tycon global_env ty_con
+             AGlobal (AConLike (RealDataCon con)) -> tcInferDataCon con
+             AGlobal (AConLike (PatSynCon ps)) -> tcInferPatSyn id_name ps
+             AGlobal (ATyCon tc) -> fail_tycon tc
+             ATcTyCon tc -> fail_tycon tc
+             ATyVar name _ -> fail_tyvar name
 
              _ -> failWithTc $
                   ppr thing <+> text "used where a value identifier was expected" }
   where
-    fail_tycon global_env ty_con =
-      let pprov = case lookupGRE_Name global_env (tyConName ty_con) of
+    fail_tycon tc = do
+      gre <- getGlobalRdrEnv
+      let msg = text "Illegal term-level use of the type constructor"
+                  <+> quotes (ppr (tyConName tc))
+          pprov = case lookupGRE_Name gre (tyConName tc) of
             Just gre -> nest 2 (pprNameProvenance gre)
             Nothing  -> empty
-      in failWithTc (term_level_tycons ty_con $$ pprov)
-
-    term_level_tycons ty_con
-      = text "Illegal term-level use of the type constructor"
-          <+> quotes (ppr (tyConName ty_con))
+      suggestions <- get_suggestions dataName
+      failWithTc (msg $$ pprov $$ suggestions)
+
+    fail_tyvar name = do
+      let msg = text "Illegal term-level use of the type variable"
+                  <+> quotes (ppr name)
+          pprov = nest 2 (text "bound at" <+> ppr (getSrcLoc name))
+      suggestions <- get_suggestions varName
+      failWithTc (msg $$ pprov $$ suggestions)
+
+    get_suggestions ns = do
+       let occ = mkOccNameFS ns (occNameFS (occName id_name))
+       dflags  <- getDynFlags
+       rdr_env <- getGlobalRdrEnv
+       lcl_env <- getLocalRdrEnv
+       imp_info <- getImports
+       curr_mod <- getModule
+       hpt <- getHpt
+       return $ unknownNameSuggestions WL_Anything dflags hpt curr_mod rdr_env
+         lcl_env imp_info (mkRdrUnqual occ)
 
     return_id id = return (HsVar noExtField (noLocA id), idType id)
 
diff --git a/testsuite/tests/module/mod132.stderr b/testsuite/tests/module/mod132.stderr
index 37c934c70f..31d9c8eeb6 100644
--- a/testsuite/tests/module/mod132.stderr
+++ b/testsuite/tests/module/mod132.stderr
@@ -1,7 +1,8 @@
 
 mod132.hs:6:7: error:
-     Illegal term-level use of the type constructor ‘Foo’
+    • Illegal term-level use of the type constructor ‘Foo’
         imported from ‘Mod132_B’ at mod132.hs:4:1-15
         (and originally defined in ‘Mod132_A’ at Mod132_A.hs:3:1-14)
-     In the expression: Foo
+      Perhaps you meant variable ‘foo’ (line 6)
+    • In the expression: Foo
       In an equation for ‘foo’: foo = Foo
diff --git a/testsuite/tests/typecheck/should_fail/T19978.hs b/testsuite/tests/typecheck/should_fail/T19978.hs
new file mode 100644
index 0000000000..fd96697db9
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T19978.hs
@@ -0,0 +1,25 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module T19978 where
+
+-----------------------------------------
+--       Type constructor in terms     --
+-----------------------------------------
+ex1 = Bool
+
+-- to be suggested instead of "Bool" in "ex1":
+data T1 = Bowl
+bool = Bowl
+
+ex2 = Let  -- should suggest Left (imported from Prelude)
+
+-----------------------------------------
+--        Type variable in terms       --
+-----------------------------------------
+
+ex3 :: forall mytv. mytv
+ex3 = mytv
+
+-- to be suggested instead of "mytv" in "ex3":
+data T3 = Mytv
+myvv = Mytv
diff --git a/testsuite/tests/typecheck/should_fail/T19978.stderr b/testsuite/tests/typecheck/should_fail/T19978.stderr
new file mode 100644
index 0000000000..7f41c37ad4
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T19978.stderr
@@ -0,0 +1,21 @@
+
+T19978.hs:8:7: error:
+    • Illegal term-level use of the type constructor ‘Bool’
+        imported from ‘Prelude’ at T19978.hs:3:8-13
+        (and originally defined in ‘GHC.Types’)
+      Perhaps you meant one of these:
+        ‘Bowl’ (line 11), variable ‘bool’ (line 12)
+    • In the expression: Bool
+      In an equation for ‘ex1’: ex1 = Bool
+
+T19978.hs:14:7: error:
+    • Data constructor not in scope: Let
+    • Perhaps you meant ‘Left’ (imported from Prelude)
+
+T19978.hs:21:7: error:
+    • Illegal term-level use of the type variable ‘mytv’
+        bound at T19978.hs:20:15
+      Perhaps you meant one of these:
+        data constructor ‘Mytv’ (line 24), ‘myvv’ (line 25)
+    • In the expression: mytv
+      In an equation for ‘ex3’: ex3 = mytv
diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index 54af02c6f5..b776f1d5dd 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -631,3 +631,4 @@ test('T19415', normal, compile_fail, [''])
 test('T19615', normal, compile_fail, [''])
 test('T17817', normal, compile_fail, [''])
 test('T17817_elab', normal, compile_fail, ['-fprint-typechecker-elaboration'])
+test('T19978', normal, compile_fail, [''])