[SR-2354] inout parameter in subscript gives the wrong error message

[swift-ci]

Previous ID	SR-2354
Radar	None
Original Reporter	chriseidhof (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, DiagnosticsQoI, Parser, StarterBug
Assignee	@CodaFi
Priority	Medium

md5: 0bbd574dd373c16d9585687e14bb250e

Issue Description:

When I try to have an `inout` parameter in a subscript, the compiler won't let me compile:

struct X {
    subscript(x: inout Int) -> () {
      x += 1
    }
}

However, the error message could be improved. The current message is: "Parameters may not have the 'var' specifier". This should probably be something like "Subscript parameters may not have the 'inout' specifier".

[belkadan]

I don't see any error at all until the call site in Swift 3, but either way we should fix this.

[swift-ci]

Comment by Ryan Collins (JIRA)

@belkadan chriseidhof (JIRA User)

I'm having trouble getting the compiler to throw this error at all. Do you have an example project?

My test project to try to get the compiler to throw that error is here: https://github.com/rymcol/SR2354 (using DEVELOPMENT-SNAPSHOT-2016-08-23-a)

[belkadan]

I think that must have just recently changed. We still reject it at the call site, though, so we probably should be rejecting it at the declaration site.

struct X {
    subscript(x: inout Int) -> () {
      x += 1
    }
}

func test(_ x: X) {
  var y = 1
  print(x[&y])
  print(y)
}
test(X())

[CodaFi]

Resolved by #9147.