Fix nullness narrowing in match inside comprehensions#19743
Open
T-Gro wants to merge 2 commits into
Open
Conversation
…#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>
Contributor
❗ Release notes required
|
T-Gro
added
AI-Auto-Resolve-Conflicts
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
github-actions
Bot
added
the
AI-Tooling-Check-Bypassed
T-Gro
commented
May 18, 2026
Member
Author
T-Gro
left a comment
T-Gro
left a comment
There was a problem hiding this comment.
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.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Fix false-positive FS3261 when pattern matching narrows nullness inside seq/list/array comprehensions.
Fixes #19644