Fix nullness narrowing in match inside comprehensions#19743
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Clean fix. The refactoring of EliminateNullnessFromInputType into a standalone function is faithful (logic is unchanged) and threading the narrowed inputTy through the List.mapFold accumulator in CheckSequenceExpressions.fs mirrors exactly how TcMatchClauses already works for normal match expressions.
Verified:
- The extracted function is logic-identical to the original inline code in
TcMatchClause condRfromTcMatchPatternisExpr option, matching the function'swhenExprOptparameter- The shadowed
inputTyin the fold correctly feeds the narrowed type into subsequent clauses'TcMatchPatterncalls TryWithin sequence expressions matches ong.exn_tyand doesn't need similar treatment- Tests cover all three comprehension flavors plus the no-for variant
- Release notes present
LGTM.
…#19644) Extract null-narrowing helper EliminateNullnessFromInputType from TcMatchClause and reuse it in TcSequenceExpression's SynExpr.Match handler so the input type is narrowed across clauses inside comprehensions, matching the behavior of plain match expressions. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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…ndency The ImmutableHashSet<int>.Builder type is not available in the net472 test compilation environment. Replace with string | null which tests the same nullness narrowing logic without requiring external assembly references. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Fix false-positive FS3261 when pattern matching narrows nullness inside seq/list/array comprehensions.
Fixes #19644