clang crashes when an enum forward declaration is used in cast

[llvmbot]

Bugzilla Link	8089
Resolution	FIXED
Resolved on	Sep 11, 2010 22:41
Version	trunk
OS	Windows NT
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor

Extended Description

test.cpp:
enum E;
int a = (E)3;

clang -cc1 -fsyntax-only test.cpp

stack dump.

[llvmbot]

So, I guess since you discovered this, this means that something actually uses this and expects it to work? Or does it come from genuinely invalid code?

The crash actually occurs when implicitly converting the incomplete enum type back to int in the initialization. We check if this is an integral promotion, and for this we attempt to get the enum's promoted type. But that type hasn't been computed for the incomplete enum, so null is returned, which we eventually access.

There's something very fishy about that code, aside from crashing.

Anyway, the question is, what result do we want for this?

[llvmbot]

I discovered this bug while investigating what is needed to support enum foward declaration in -fms-extensions mode. MSVC allows such code to compile.

I am preparing a patch to assign an underying type to an incomplete enum in msvc mode.

Without -fms-extensions we just want clang to emit a meaningful diagnostic instead of crashing.

[DougGregor]

Fixed in Clang r113711.