labath added a comment.
I'm going to respond to the rest of your (very insightful) comment later. So
far, I'm just responding to this:
>> This isn't exactly layout related, but there is the question of covariant
>> methods. If a method is covariant, then its return type must be complete.
>
> We already import all the base classes of a derived class (at least in full
> import). But, we do not import all the derived classes during the import of
> the base. Is this what you do in LLDB to support covariant return types?
This situation is a bit tricky to explain as there are two independent class
hierarchies that need to be considered. Let me start with an example:
struct B1;
struct B2;
struct A1 { B1 *f(); };
struct A2 { B2 *f(); };
This is a perfectly valid C++ snippet. In fact it could be extended to also
implement `A1::f` and `A2::f` and call them and it would still not require the
definitions for structs `B1` and `B2`. And I believe the ast importer will
would not import their definitions even if they were available. It certainly
wouldn't force them to be defined (`getExternalSource()->CompleteType(B1)`).
This changes if the methods become virtual. In this case, this code becomes
valid only if `B2*` is convertible to `B1*` (i.e., `B2` is derived from `B1`).
To know that, both `B1` and `B2` have to be complete. Regular clang parser will
enforce that, and codegen will depend on it. However, the AST importer will not
automatically import these classes. Lldb's code to do that is here
https://github.com/llvm/llvm-project/blob/fdc6aea3fd822b639baaa5b666fdf7598d08c8de/lldb/source/Plugins/ExpressionParser/Clang/ClangASTImporter.cpp#L994.
I don't know whether something like this would be in scope for the default ast
importer, but it seemed useful to mention in the context of the present
discussion.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D86660/new/
https://reviews.llvm.org/D86660
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
