Bad diagnostic when inheriting from class in extension #64903
Description
The following errors are misleading and could use a rewording as clear language rules, depending on the kinds of extended and inherited types.
protocol P {} struct S {} class C1 {} class C2 {} extension C2: S {} // error: inheritance from non-protocol type 'S' extension C2: C1 {} // error: inheritance from non-protocol type 'C1' extension C2: C1 & P {} // error: inheritance from class-constrained protocol composition type 'C1 & P'Environment
- Swift version 5.9-dev (LLVM 6a04c4848990c70, Swift c1d5118)
NB: How to improve on these is left as an exercise to whoever takes the issue.
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A deviation from expected or documented behavior. Also: expected but undesirable behavior.The Swift compiler itselfBug: Diagnostics Quality of ImplementationFeature → declarations: `extension` declarationsGood for newcomersFeature → type declarations → class: Subclassing and inheritance of class membersArea → compiler: Semantic analysis