[SR-1924] locally defined class after return crashes compiler

[mattneub]

Previous ID	SR-1924
Radar	None
Original Reporter	@mattneub
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode Version 8.0 beta (8S128d) and its version of Swift 3

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, CompilerCrash
Assignee	@slavapestov
Priority	Medium

md5: 1a0dc260ae3d2d9a42ce72bd4313424b

Issue Description:

This code crashes the compiler with a segfault:

    func test() {
        return;
        class A {
            
        }
    }

Neither the return; nor the locally defined class A is illegal. It's the combination of the two that's the problem: defining a class locally, at any depth, after a return seems to elicit the crash.

[slavapestov]

The AST is valid, however SILGen erroneously skips emitting the class because it thinks it's "code" that is unreachable.

[slavapestov]

Actually, since name lookup can't see the class in this case, it would be more correct to drop it altogether.

[slavapestov]

#6543