aaron.ballman added inline comments.
================
Comment at: clang/include/clang/AST/DeclCXX.h:3801
+/// error.
+class UnresolvedUsingIfExistsDecl final : public NamedDecl {
+ UnresolvedUsingIfExistsDecl(DeclContext *DC, SourceLocation Loc,
----------------
erik.pilkington wrote:
> aaron.ballman wrote:
> > erik.pilkington wrote:
> > > aaron.ballman wrote:
> > > > Why is this inheriting from a `NamedDecl` rather than a `UsingDecl`?
> > > > Given that this is a type of using declaration, I guess I would have
> > > > expected it to appear as such in the AST hierarchy. For instance,
> > > > should people using AST matchers be able to match one of these as a
> > > > using declaration or are they so different semantically that they need
> > > > to be sibling AST nodes?
> > > This node isn't a kind of using declaration, it is a declaration that
> > > gets inserted into the scope via a usual UsingDecl & UsingShadowDecl
> > > mechanism that Sema knows to error out on if it is ever used. So
> > > presumably existing AST users would still recognize that this is a
> > > UsingDecl that adds a single declaration into the current context, but
> > > wouldn't really know anything about that declaration. I updated the doc
> > > comment above to make that more clear.
> > So given code like this:
> > ```
> > using empty_namespace::does_not_exist __attribute__((using_if_exists));
> > ```
> > would you expect this AST matcher to match or not?
> > ```
> > usingDecl()
> > ```
> > (I hope the answer is "yes" because otherwise the behavior is rather
> > inexplicable to me.)
> Yeah, the answer is "yes". The AST representation for a using_if_exists
> declaration that failed to lookup anything would look something like this:
>
> ```
> |-UsingDecl 0x7fa42b84a3a0 <t.cpp:20:1, col:9> col:9 ::X
> |-UsingShadowDecl 0x7fa42b84a3f8 <col:9> col:9 implicit
> UnresolvedUsingIfExists 0x7fa42b84a370 'X'
> ```
>
> So its still using the typical UsingDecl machinery, its just that the
> declaration thats being imported is different.
Awesome, thank you for clarifying!
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D90188/new/
https://reviews.llvm.org/D90188
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