hokein added a comment.
In D99165#2644243 <https://reviews.llvm.org/D99165#2644243>, @sammccall wrote:
> The fix doesn't look obviously correct: the side effect of marking the
> destructor reference seems important if we actually generate code. It's not
> obvious to me why the type can only be incomplete if there are errors.
>
> This was introduced between clang 8 and clang 9, I would guess by
> f8ccf052935adaf405e581fd31e8bc634cc5bbc7.
> @erik.pilkington
> Looking at that patch, mostly this function was just a rename, but there's a
> new callsite for array-types that seems to be what we're hitting here.
> Maybe a slightly less-invasive version would be to guard that callsite with
> "and if the element type is complete"?
ok, after taking a closer look on the crash, you're right. fixing
checkDestructorReference or guarding at that particular callsite is not a root
fix.
I managed to reduce a smaller case `ForwardClass array[var_size] = {0};`, and
the crash occurs when clang is performing an initializer check on an
incomplete-type var decl, this should not be happened --
because an incomplete type of decl should be marked invalid in clang (e.g.
`ForwardClass array[var_size];`, `ForwardClass var;`), but for the crash case,
the type of variable-length array is not treated as an incomplete type (this is
the bug),
thus the var decl is considered valid, and clang performs the initializer check
on it.
So I think the right solution is to fix type of variable-length array -- if the
element type of the variable-length array is incomplete, then the type of array
is incomplete.
================
Comment at: clang/lib/AST/Type.cpp:2234
// (C++ [dcl.array]p1).
- // We don't handle variable arrays (they're not allowed in C++) or
- // dependent-sized arrays (dependent types are never treated as
incomplete).
----------------
This comment is pretty old, and was added in
2dfdb820ca550f75769f6850bc27f825f1dce4f7 in 2009. I don't think this is correct
anymore, variable-length array is allowed in C++, and from
http://eel.is/c++draft/basic.types.general#5,
> an array of unknown bound or of incomplete element type, is an
> incompletely-defined object type.36 Incompletely-defined object types and cv
> void are incomplete types
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