Fix a bunch of cases where we use the same external name to mean
multiple different things in the same test. We've historically gotten
away with this, but under `--share-cpp-ast`, it becomes an error, at
least if the entity is either defined in, or used from, C++ code.
Assisted-by: Gemini via Antigravity (original change) and Claude Code
(suggested edits in review)
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Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
When a Carbon virtual function overrides a C++ virtual function, we need
to export it with the C++ signature in order for it to work as an
override. Instead of mapping the C++ signature into Carbon and then back
again, use the original C++ signature from the base class as the
signature exported to C++.
Also add documentation explaining how we use thunks in C++ interop,
including in this new virtual function handling logic.
For now, disable the use of array types as by-var paramters and by-init
return types when exporting Carbon functions to C++, as C++ does not
support raw arrays being passed or returned by value.
Assisted-by: Gemini via Antigravity
Richard SmithandChandler Carruth