[SR-14265] Warn when trying to override the range values in a loop

[swift-ci]

Previous ID	SR-14265
Radar	rdar://problem/74652010
Original Reporter	arlomedia (JIRA User)
Type	Improvement

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement, DiagnosticsQoI
Assignee	None
Priority	Medium

md5: 24c62d084c635252a16671e4ed35b018

Issue Description:

I'm converting a project from Objective-C, and I have a few cases where I change the index of a for loop on the fly, like this:

for (int i=1; i<[items count]; i++) {
    if ([[items objectAtIndex:i] hasPrefix:@"-"]) {
        isGroup = TRUE;
        i = i + 3;
    }
}

After converting to Kotlin, I didn't see any compiler warnings or errors, so I expected this to work the same way:

for var i in 0..<items.count {
    if items[i].hasPrefix("-") {
        isGroup = true
        i = i + 3
    }
}

But the change to i is essentially ignored (reset on each iteration). I've since found some explanations of why this behaves the way it does, and I can rewrite the code to get the same behavior. But I would like to see the compiler flag this so I know it's a problem before it shows up as a bug in my app.

The same construct works in Java and Kotlin, so this change would also help developers coming from those languages.

[typesanitizer]

@swift-ci create