[6.3][CSSimplify] Parameter pack wrapping logic incorrectly considers tuple LValueTypes to not be tuples #85962 #86016
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…e `LValueType`s to not be tuples (swiftlang#85962) In swiftlang#65125 (and beyond) `matchTypes`, has logic to attempt to wrap an incoming parameter in a tuple under certain conditions that might help with type expansion. In the case the incoming type was backed by a `var`, it would be wrapped by an `LValueType` then be subsequently mis-diagnosed as not-a-tuple. More details in swiftlang#85924 , this this is also the cause of (and fix for) swiftlang#85837 as well...
slavapestov
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Dec 12, 2025
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@swift-ci Please test |
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Explanation: When passed
lvalue'd parameters, functions returning parameter packs would not flatten thelvalue'd parameters (for example passing in anything from avar), causing incorrect tuple nesting.Scope: Fixes an issue tha caused incorrect result typing for parameter pack results if a parameter is a
var. This behavior is unavoidable in ResultBuilders, causing them to be somewhat broken.Issues: Parameter packed functions pack less efficiently if the input is a
var#85924 and ResultBuilders do not produce efficient parameter pack types #85837Original PRs: [CSSimplify] Parameter pack wrapping logic incorrectly considers tuple
LValueTypes to not be tuples #85962Risk: Low/Medium - Some risk to existing code, iff it explicitly depends on the incorrect behavior. The behavior has likely been worked around already in most cases, though.
Testing: Tests for expected new/fixed behavior are in the PR, which also show #85837 to be resolved.
Reviewers: @xedin @slavapestov
(Cherry picking fe0191c)