[SR-15096] Add diagnostic for usage of 'open' extension methods on pure Swift classes #57422
Description
| Previous ID | SR-15096 |
| Radar | None |
| Original Reporter | @typesanitizer |
| Type | Bug |
| Status | In Progress |
| Resolution |
Additional Detail from JIRA
| Votes | 0 |
| Component/s | Compiler |
| Labels | Bug |
| Assignee | mininny (JIRA) |
| Priority | Medium |
md5: f58fc20f557cce2f2ade639d7c1ce432
Issue Description:
The following code snippet:
public class C { }
extension C {
open func f() { }
}compiles without a diagnostic today. Superficially, it might seem like you can override f from a subclass of C. However, that's not the case; you can only overload it. Being able to override methods declared in extensions would require a mechanism like objc_msgSend, which is why such overloading only works when @objc is present, there is no Swift equivalent for pure Swift classes.
This means that the open is misleading to a reader; we should issue a diagnostic with a fix-it to replace this with public instead in such situations.