282df905
by Vladislav Zavialov at 2025-05-09T03:18:25-04:00
Take subordinate 'type' specifiers into account
This patch fixes multiple bugs (#22581, #25983, #25984, #25991)
in name resolution of subordinate import lists.
Bug #22581
----------
In subordinate import lists, the use of the `type` namespace specifier
used to be ignored. For example, this import statement was incorrectly
accepted:
import Prelude (Bool(type True))
Now it results in an error message:
<interactive>:2:17: error: [GHC-51433]
In the import of ‘Prelude’:
a data type called ‘Bool’ is exported,
but its subordinate item ‘True’ is not in the type namespace.
Bug #25983
----------
In subordinate import lists within a `hiding` clause, non-existent
items led to a poor warning message with -Wdodgy-imports. Consider:
import Prelude hiding (Bool(X))
The warning message for this import statement used to misreport the
cause of the problem:
<interactive>:3:24: warning: [GHC-56449] [-Wdodgy-imports]
In the import of ‘Prelude’:
an item called ‘Bool’ is exported, but it is a type.
Now the warning message is correct:
<interactive>:2:24: warning: [GHC-10237] [-Wdodgy-imports]
In the import of ‘Prelude’:
a data type called ‘Bool’ is exported, but it does not export
any constructors or record fields called ‘X’.
Bug #25984
----------
In subordinate import lists within a `hiding` clause, non-existent
items resulted in the entire import declaration being discarded.
For example, this program was incorrectly accepted:
import Prelude hiding (Bool(True,X))
t = True
Now it results in an error message:
<interactive>:2:5: error: [GHC-88464]
Data constructor not in scope: True
Bug #25991
----------
In subordinate import lists, it was not possible to refer to a class
method if there was an associated type of the same name:
module M_helper where
class C a b where
type a # b
(#) :: a -> b -> ()
module M where
import M_helper (C((#)))
This import declaration failed with:
M.hs:2:28: error: [GHC-10237]
In the import of ‘M_helper’:
an item called ‘C’ is exported, but it does not export any children
(constructors, class methods or field names) called ‘#’.
Now it is accepted.
Summary
-------
The changes required to fix these bugs are almost entirely confined to
GHC.Rename.Names. Other than that, there is a new error constructor
BadImportNonTypeSubordinates with error code [GHC-51433].
Test cases:
T22581a T22581b T22581c T22581d
T25983a T25983b T25983c T25983d T25983e T25983f T25983g
T25984a T25984b
T25991a T25991b1 T25991b2