[SR-7251] Redeclaring a variable with a type in a generic extension doesn't error

[hamishknight]

Previous ID	SR-7251
Radar	None
Original Reporter	@hamishknight
Type	Bug
Status	Closed
Resolution	Done

Environment

Swift version 4.2-dev (LLVM cef3fe6d75, Clang bdc970d89c, Swift 5b60ace)
Target: x86_64-apple-darwin17.4.0

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	@hamishknight
Priority	Medium

md5: 455775109cfbec5e12494dbe7e1b6c61

Issue Description:

This correctly doesn't compile:

struct S {}
extension S {
  static var i: Int { return 0 }
  struct i {} // error: Invalid redeclaration of 'i'
}

But this does compile:

struct S1<T> {}
extension S1 {
  static var i: Int { return 0 }
  struct i {} // This is fine!
}

[hamishknight]

#15412

[belkadan]

Any fixes here are going to have to be limited to Swift 5 mode, since someone might be relying on them in Swift 4.

[hamishknight]

Fixed in the above linked pull request; the redeclaration will be warning in Swift 4 mode and an error in Swift 5 mode.