sammccall added a subscriber: rsmith.
sammccall added a comment.
Neither of the testcases look like the right behavior to me, and I think the
bug is elsewhere in clang.
The crux is we're forcing `decltype(N)` to be a (unique) dependent type, which
feels wrong.
This isn't specific to error-dependence, the same is true in
template <int K> void foo() {
constexpr int N = K;
decltype(K) // dependent?
}
ASTContext::getDecltypeType() has to determine whether
http://eel.is/c++draft/temp.type#4 applies.
There are three behaviors:
- standard up to C++14: traversing the expr looking for a template param to be
lexically included (this is my reading of the standard)
- what clang actually does: check instantiation dependence, which I think pulls
in too many cases
- standard after http://wg21.link/cwg2064: check type dependence
I think it's probably OK to adopt the C++17 behavior for all versions (if I'm
right that the current behavior is a bug).
@rsmith It's your DR, what do you think :-)
(Per offline discussion, this was reduced from a related bug that didn't
involve decltype, but I think we should treat that one as distinct)
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D86048/new/
https://reviews.llvm.org/D86048
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