Return MissingPatternSyntax for empty pattern positions#3329
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Return MissingPatternSyntax for empty pattern positions#3329broken-circle wants to merge 1 commit into
MissingPatternSyntax for empty pattern positions#3329broken-circle wants to merge 1 commit into
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When `parseMatchingPattern()` reaches its expression-fallback path, it
calls `parseSequenceExpression()` and wraps the result in a
`RawExpressionPatternSyntax`. If the current token starts neither a
pattern nor an expression, this produces a missing expression wrapped
in an expression-pattern, which the diagnostic engine describes as a
missing expression rather than a missing pattern.
Instead, return `RawMissingPatternSyntax` directly before the fallback.
For example, `switch x { case }` now produces "expected pattern..."
rather than "expected expression...".
Closes swiftlang#3158.
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Closes #3158.
When parsing code such as these snippets:
parseMatchingPattern()reaches its expression-fallback path, callsparseSequenceExpression(), and wraps the result in aRawExpressionPatternSyntax. If the current token starts neither a pattern nor an expression, this produces a missing expression wrapped in an expression-pattern, which the diagnostic engine describes as a missing expression rather than a missing pattern.This PR adds an early return of
RawMissingPatternSyntaxbefore the expression fallback, which fires if the current token is neither an expression nor the start of a pattern. The fallback still fires for ambiguous forms. Now, the above examples produce "expected pattern..." diagnostics.Testing
Updated
ExpressionTests.testStandaloneAtCaseInSwitch(),StatementTests.testIf(),RecoveryTests.testRecovery180(), andSwitchTests.testSwitch4()to expect the correct diagnostics.Added
StatementTests.testIfCaseWithMissingPattern()andSwitchTests.testSwitch4b()to coverif case = xandcase :, respectively.All tests pass when run locally.