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Fix: preserve type applications in record patterns #1680

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Fix: preserve type applications in record patterns #1680

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14 changes: 12 additions & 2 deletions src/Hint/Pattern.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -198,9 +198,19 @@ asPattern (L loc x) = concatMap decl (universeBi x)

-- First Bool is if 'Strict' is a language extension. Second Bool is
-- if this pattern in this context is going to be evaluated strictly.
-- Check if a type argument is just a wildcard (can be omitted)
-- Returns True only if the type arg is @_ or similar wildcard notation
isWildcardTypeArg :: HsConPatTyArg GhcPs -> Bool
isWildcardTypeArg tyarg =
let s = unsafePrettyPrint tyarg
-- Normalize: remove whitespace and check if it becomes just "_"
normalized = filter (not . (`elem` " \t\n")) s
in normalized == "_" || normalized == "@_"

patHint :: Bool -> Bool -> LPat GhcPs -> [Idea]
patHint _ _ o@(L _ (ConPat _ name (PrefixCon _ args)))
| length args >= 3 && all isPWildcard args =
patHint _ _ o@(L _ (ConPat _ name (PrefixCon tyargs args)))
| all isWildcardTypeArg tyargs -- Only suggest if all type args are wildcards (or none)
, length args >= 3 && all isPWildcard args =
let rec_fields = HsRecFields noExtField [] Nothing :: HsRecFields GhcPs (LPat GhcPs)
new = noLocA $ ConPat noAnn name (RecCon rec_fields) :: LPat GhcPs
in
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