[SR-297] Overflow not trapped in generic function

[jepers]

Previous ID	SR-297
Radar	rdar://22936450
Original Reporter	@jepers
Type	Bug

Environment

OS X 10.11.2, Swift version 2.2-dev (LLVM 3ebdbb2c7e, Clang f66c5bb67b, Swift 69940d1)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 266267f2264d51f0997250ad08fd57d0

Issue Description:

$ cat > t.swift
func foo<T: UnsignedIntegerType>(_: T.Type) -> T { return -1 }
if foo(UInt8) == 255 { print("Overflow is not trapped 1.") }
func bar<T: UnsignedIntegerType>(_: T.Type) -> T {
    let uintVal: T = -1
    return uintVal
}
if bar(UInt8) == 255 { print("Overflow is not trapped 2.") }

$ swiftc t.swift && ./t
Overflow is not trapped 1.
Overflow is not trapped 2.

[karwa]

@DougGregor this looks like the same issue we discussed:

func getValue<T>() -> T where T:ExpressibleByIntegerLiteral { 
     return 1000 
}
getValue() as UInt8 // returns 232. No warnings.

This also affects the generated RawRep conformance for enums when the raw type is generic.

[DougGregor]

Ah, yes, it is. Something in the integer literal protocols is dodging the overflow checking.