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Implement support for copying C++ classes. (#6434)

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When performing impl lookup for `Core.Copy` for a C++ class type, look
for a copy constructor. If we find one, synthesize an impl witness that
calls the constructor.

This adds initial support for impl lookup to delegate to the C++ interop
logic for queries involving C++ types. For now, we don't implement the
rules from #6166 that compare a synthesized type structure for the C++
impl against the best Carbon type structure, but the framework for
building that support is established here.

Currently there is no caching of the lookup here, and we build unique
`ImplWitnessTable`s for each lookup, which leads to each impl lookup
producing a distinct facet value. This results in some errors in generic
contexts; this will be addressed in follow-up changes. This PR aims only
to support the non-generic case.

---------

Co-authored-by: Dana Jansens <danakj@orodu.net>
Co-authored-by: Carbon Infra Bot <carbon-external-infra@google.com>
This commit is contained in:
Richard Smith
2025-12-02 02:52:23 +00:00
committed by GitHub
co-authored by Dana Jansens Carbon Infra Bot
parent 19660ccde0
commit 372f632d9d
16 changed files with 923 additions and 127 deletions
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toolchain/check/cpp/overload_resolution.cpp
-1
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@@ -162,7 +162,6 @@ auto PerformCppOverloadResolution(Context& context, SemIR::LocId loc_id,
case clang::OverloadingResult::OR_Success: {
CARBON_CHECK(best_viable_fn->Function);
CARBON_CHECK(!best_viable_fn->RewriteKind);
sema.MarkFunctionReferenced(loc, best_viable_fn->Function);
SemIR::InstId result_id = ImportCppFunctionDecl(
context, loc_id, best_viable_fn->Function, arg_exprs.size());
if (auto fn_decl =