[Git][ghc/ghc][wip/fabu/T24452-confusing-error] compiler: Fix emitting a confusing error for non visible class method
Fabricio Nascimento (@fabu)
gitlab at gitlab.haskell.org
Fri Jun 21 14:03:10 UTC 2024
Fabricio Nascimento pushed to branch wip/fabu/T24452-confusing-error at Glasgow Haskell Compiler / GHC
Commits:
5fe709ef by Fabricio de Sousa Nascimento at 2024-06-21T22:57:22+09:00
compiler: Fix emitting a confusing error for non visible class method
While solving for class methods on the GRE, if the method with the right
parent is not visible, but more than one other class methods with the
same name are, GHC would report ambiguous names, when in fact the correct
error message would be that the expected class method is not visible.
Fixes #24452
- - - - -
11 changed files:
- compiler/GHC/Rename/Env.hs
- + testsuite/tests/rename/T24452/T24452a.hs
- + testsuite/tests/rename/T24452/T24452b.hs
- + testsuite/tests/rename/T24452/T24452b.stderr
- + testsuite/tests/rename/T24452/T24452c.hs
- + testsuite/tests/rename/T24452/T24452c.stderr
- + testsuite/tests/rename/T24452/T24452d.hs
- + testsuite/tests/rename/T24452/T24452d.stderr
- + testsuite/tests/rename/T24452/T24452e.hs
- + testsuite/tests/rename/T24452/T24452e.stderr
- + testsuite/tests/rename/T24452/all.T
Changes:
=====================================
compiler/GHC/Rename/Env.hs
=====================================
@@ -708,8 +708,8 @@ lookupSubBndrOcc_helper must_have_parent warn_if_deprec parent rdr_name how_lkup
else checkFld g
DisambiguatedOccurrence g ->
checkFld g
- AmbiguousOccurrence gres ->
- mkNameClashErr gres
+ AmbiguousOccurrence _ ->
+ noMatchingParentErr original_gres
where
checkFld :: GlobalRdrElt -> RnM ChildLookupResult
checkFld g = do
@@ -721,21 +721,25 @@ lookupSubBndrOcc_helper must_have_parent warn_if_deprec parent rdr_name how_lkup
-- 1. There were none to begin with.
-- 2. None of the matching ones were the parent but
-- a. They were from an overloaded record field so we can report
- -- a better error
+ -- a better error.
-- b. The original lookup was actually ambiguous.
-- For example, the case where overloading is off and two
-- record fields are in scope from different record
- -- constructors, neither of which is the parent.
+ -- constructors, neither of which is the parent. Or two or more
+ -- class methods with the same name are in scope, in which case
+ -- we want to report we did not find the method for the expected
+ -- parent, instead of a clashing name error, which would be confusing
+ -- and point the user the wrong direction (#24452).
noMatchingParentErr :: [GlobalRdrElt] -> RnM ChildLookupResult
noMatchingParentErr original_gres = do
- traceRn "npe" (ppr original_gres)
+ traceRn "noMatchingParentErr" (ppr original_gres)
dup_fields_ok <- xoptM LangExt.DuplicateRecordFields
case original_gres of
[] -> return NameNotFound
[g] -> return $ IncorrectParent parent g
[p | ParentIs p <- [greParent g]]
gss@(g:gss'@(_:_)) ->
- if all isRecFldGRE gss && dup_fields_ok
+ if must_have_parent || dup_fields_ok && all isRecFldGRE gss
then return $
IncorrectParent parent g
[p | x <- gss, ParentIs p <- [greParent x]]
=====================================
testsuite/tests/rename/T24452/T24452a.hs
=====================================
@@ -0,0 +1,13 @@
+-- A program with empty (Alternative.empty, Map.empty, Set.empty) builds
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module BugReproduce where
+
+import Control.Applicative (Alternative (empty, (<|>)))
+import qualified Data.Map as Map
+import qualified Data.Set as Set
+
+newtype Foo a = MkFoo [a] deriving (Functor, Applicative)
+
+instance Alternative Foo where
+ empty = undefined
+ p <|> q = undefined
=====================================
testsuite/tests/rename/T24452/T24452b.hs
=====================================
@@ -0,0 +1,10 @@
+-- Alternative.empty is not visible
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module BugReproduce where
+
+import Control.Applicative (Alternative)
+
+newtype Foo a = MkFoo [a] deriving (Functor, Applicative)
+
+instance Alternative Foo where
+ empty = undefined
=====================================
testsuite/tests/rename/T24452/T24452b.stderr
=====================================
@@ -0,0 +1,2 @@
+T24452b.hs:10:3: error: [GHC-54721]
+ ‘empty’ is not a (visible) method of class ‘Alternative’
\ No newline at end of file
=====================================
testsuite/tests/rename/T24452/T24452c.hs
=====================================
@@ -0,0 +1,11 @@
+-- Having Map.empty present, does not change the fact that Alternative.empty is not visible
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module BugReproduce where
+
+import Control.Applicative (Alternative)
+import qualified Data.Map as Map
+
+newtype Foo a = MkFoo [a] deriving (Functor, Applicative)
+
+instance Alternative Foo where
+ empty = undefined
=====================================
testsuite/tests/rename/T24452/T24452c.stderr
=====================================
@@ -0,0 +1,2 @@
+T24452c.hs:11:3: error: [GHC-54721]
+ ‘empty’ is not a (visible) method of class ‘Alternative’
\ No newline at end of file
=====================================
testsuite/tests/rename/T24452/T24452d.hs
=====================================
@@ -0,0 +1,12 @@
+-- Multiple other empty (Map.empty, Data.empty), but the issue still Alternative.empty not visible.
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module BugReproduce where
+
+import Control.Applicative (Alternative)
+import qualified Data.Map as Map
+import qualified Data.Set as Set
+
+newtype Foo a = MkFoo [a] deriving (Functor, Applicative)
+
+instance Alternative Foo where
+ empty = undefined
=====================================
testsuite/tests/rename/T24452/T24452d.stderr
=====================================
@@ -0,0 +1,2 @@
+T24452d.hs:12:3: error: [GHC-54721]
+ ‘empty’ is not a (visible) method of class ‘Alternative’
\ No newline at end of file
=====================================
testsuite/tests/rename/T24452/T24452e.hs
=====================================
@@ -0,0 +1,24 @@
+-- Multiple unrelated errors related to empty.
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE OverloadedRecordDot #-}
+{-# LANGUAGE OverloadedRecordUpdate #-}
+
+module BugReproduce where
+
+import Control.Applicative (Alternative)
+import qualified Data.Map as Map
+import qualified Data.Set as Set
+
+data A = A {
+ empty :: ()
+}
+data B = B {
+ empty :: ()
+}
+
+foo = empty
+
+newtype Foo a = MkFoo [a] deriving (Functor, Applicative)
+
+instance Alternative Foo where
+ empty = undefined
\ No newline at end of file
=====================================
testsuite/tests/rename/T24452/T24452e.stderr
=====================================
@@ -0,0 +1,10 @@
+T24452e.hs:19:7: error: [GHC-87543]
+ Ambiguous occurrence ‘empty’.
+ It could refer to
+ either the field ‘empty’ of record ‘A’,
+ defined at T24452e.hs:13:5,
+ or the field ‘empty’ of record ‘B’,
+ defined at T24452e.hs:16:5.
+
+T24452e.hs:24:3: error: [GHC-54721]
+ ‘empty’ is not a (visible) method of class ‘Alternative’
\ No newline at end of file
=====================================
testsuite/tests/rename/T24452/all.T
=====================================
@@ -0,0 +1,5 @@
+test('T24452a', normal, compile, [''])
+test('T24452b', normal, compile_fail, [''])
+test('T24452c', normal, compile_fail, [''])
+test('T24452d', normal, compile_fail, [''])
+test('T24452e', normal, compile_fail, [''])
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5fe709efbb988fd6e2b87fef3e92f6d738143f1e
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5fe709efbb988fd6e2b87fef3e92f6d738143f1e
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