[SR-9793] Inappropriate diagnostics for access level of protocol witness declared in extension

[swift-ci]

Previous ID	SR-9793
Radar	None
Original Reporter	dingobye (JIRA User)
Type	Bug
Status	In Progress
Resolution

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, DiagnosticsQoI
Assignee	dingobye (JIRA)
Priority	Medium

md5: ba9e8e59c03a898fcdd3ceb5bd065720

Issue Description:

If the access level of a protocol witness does not satisfies a requirement, the compiler suggests marking it as the required level. This is not suitable when the witness is in an extension that forbids the required level.

For example, in the following case, the note suggests marking foo() as 'internal'. However, it would conflict with 'private' extension.

internal protocol Proto {
  func foo()
}
public struct S : Proto {
}
private extension S {
  func foo() {} // note: mark the instance method as 'internal' to satisfy the requirement
}