Fixes link failures when referencing a symbol involving a fingerprint
from a different package.
Previously we included the `Namespace`'s `import_id` as part of its
fingerprint, which caused local and imported namespaces to get different
fingerprints. We now store the `import_id` on the `NameScope` instead of
on the `Namespace` inst to avoid this problem.
Also, when we reach a package-level `NameScopeId`, consistently
fingerprint it as a (package name, library name) pair. Previously the
fingerprinting depended on whether it was imported or not, as an
imported `NameScopeId` had a parent scope (the current package). We need
to include the library name here so that private entities with the same
name in different libraries have different fingerprints.
This allows Clang to correctly generate the vtable for the exported
class.
There's still something wrong with new virtual functions in the Carbon
type (left a TODO) - I thought it might be related to not flagging
the CXXMethodDecl as virtual, but my initial experiments don't seem to
back that up, so I'll look into it further separately.
There's also a test regression due to an virtual (well, abstract
specifically, but I think it'd happen with a virtual one too) function
in an abstract class taking `self` by value being rejected since
the abstract class can't be instantiated. Not sure if this is a correct
change - the test's behavior could be preserved by using `ref self`
instnead of `self` in this function. Is that reasonable/expected? Should
we not require a type to be complete when passing by value if we can
compute the value representation without such completeness?
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Not every entry in a C++ vtable corresponds to a function that we want
to import. For the holes, leave a `SemIR::InstId::None` in the vtable.
Also mark vtables that extend a C++ vtable as being non-Carbon-native so
we don't try to lower them (and crash on the `None` entries).
In particular, we leave holes for destructors, since we don't have
destructor declarations on the Carbon side that need to override them.
* For Carbon `base class C`, export as a regular C++ class.
* For Carbon `class C`, export with the C++ `final` keyword attribute.
* For Carbon `abstract C`, mark the destructor as pure virtual in cases
where no member function is abstract, or emit an error if the destructor
is not virtual.
To support the final point, mark the destructor of an exported class as
virtual if it overrides a virtual destructor from the base class.
In passing, fix a crash exporting fields if the class has an invalid
base type.
Richard Smith
David Blaikie
josh11bandJosh L