Fix Crashes when Capture-set Parameters Conflict with Terms #25029
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bracevac
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Perhaps we should also rule out nonsense like |
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When reporting a naming conflict for a PhantomSymbol, we attempt to use its companionClass for a better error message. However, companionClass can return NoSymbol when no companion exists, and accessing .owner on NoSymbol throws NoDenotation.owner assertion error. This fix checks if the companion exists before using it, falling back to the original conflicting symbol otherwise. Fixes scala#25025
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Pull request overview
This PR fixes compiler crashes (NoDenotation.owner and ClassCastException) that occurred when capture-set parameters ([c^]) conflict with term definitions of the same name in Scala's experimental capture checking feature. The fix adds proper error detection and reporting with clear, informative error messages.
Changes:
- Fixed
NoDenotation.ownercrash by using.orElse()whencompanionClassreturnsNoSymbol - Fixed
ClassCastExceptionby adding pattern matching to handle cases where widened type is not aTypeRef - Added proactive conflict detection in
addDummyTermCaptureParamto catch term parameter before capture parameter pattern - Enhanced error messages for capture-set conflicts with proper categorization and explanations
Reviewed changes
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Show a summary per file
| File | Description |
|---|---|
tests/neg-custom-args/captures/i25025.scala |
Test cases covering various capture-set parameter conflict scenarios |
tests/neg-custom-args/captures/i25025.check |
Expected error messages with proper error codes (E161) |
compiler/src/dotty/tools/dotc/typer/Namer.scala |
Fixed crash by safely handling NoSymbol from companionClass |
compiler/src/dotty/tools/dotc/typer/Typer.scala |
Fixed crash by pattern matching widened type before casting |
compiler/src/dotty/tools/dotc/core/NamerOps.scala |
Added conflict detection for term-before-capture parameter ordering |
compiler/src/dotty/tools/dotc/reporting/messages.scala |
Enhanced error message handling for capture-set conflicts |
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Fixes #25025
This PR fixes compiler crashes and adds proper error reporting when capture-set parameters (
[c^]) conflict with term definitions of the same name.Fixes
NoDenotation.ownercrash whencompanionClassreturnsNoSymbolClassCastExceptionintypedSingletonTypeTreewhen widened type isn't aTypeRefdef foo(c: AnyRef^)[c^]pattern (term param before capture param)Improvements
AlreadyDefinedmessage class to handle capture-set conflicts with proper error code (E161) and explanation