[Sema] Avoid applying diagnostic hack to caller-side expression macros #82724
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Split out the state mutation into a new `updateFor` function that we call for diagnostic emission, allowing `DiagnosticTransaction::hasErrors` to query the behavior without mutating any state.
We can't assume that type-checking the expression macro in the parameter will also fail if it fails at the call site since e.g name lookup may differ. Make sure we only apply this logic to simple literals. rdar://154771596
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@swift-ci please test |
xedin
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Jul 2, 2025
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When type-checking a caller-side expression macro default argument in a context where name lookup is unable to resolve it (but is able to resolve it in the parameter), we were previously exiting with a non-zero exit code without emitting any diagnostic. This was due to the fact that
DiagnosticState::determineBehavioris stateful, meaning that queryingDiagnosticTransaction::hasErrorscould flip the "had error" bit for the DiagnosticEngine even if the transaction got later aborted.This PR splits off the stateful bit of
DiagnosticState::determineBehaviorinto a new function that we call during diagnostic emission. This then exposed the actual underlying issue here, which is that the diagnostic hack we have for caller-side default arguments, where we expect them to fail in the parameter if they fail at the call-site, is unsound for expression macros since name lookup may differ depending on context. Limit the hack such that it only applies to simple literals (magic literals +nil,[], and[:]).rdar://154771596