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Support signature mismatch between virtual fn and override fn. (#7198)

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For now, hide `override fn`s from name lookup, so that the base class
version is always used, as the derived-class version does not have its
own vptr entry and so would not do the right thing if a further-derived
class adds a new override. This is implemented via a new access kind of
`Hidden`.

When checking the overriding function, pass in the expected `Self` type
and check the `self` parameter against that; the signature that we
generate for the thunk in the derived class is the base class signature
with the `self` parameter's type changed to the derived class.

When we generate a thunk for a virtual function, the thunk is assigned a
`virtual_index`, and the virtual function itself is not. When the thunk
makes a direct call to the virtual function, recognize this situation by
checking for a `virtual_index`, and perform a non-virtual call if there
isn't one.

Assisted-by: Gemini via Antigravity
This commit is contained in:
Richard Smith
2026-05-13 17:40:45 +00:00
committed by GitHub
parent 0b47efa57a
commit c33fb9fc48
18 changed files with 427 additions and 110 deletions
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toolchain/check/class.cpp
+20 -7
View File
@@ -16,6 +16,7 @@
#include "toolchain/check/name_ref.h"
#include "toolchain/check/pattern.h"
#include "toolchain/check/pattern_match.h"
#include "toolchain/check/thunk.h"
#include "toolchain/check/type.h"
#include "toolchain/parse/node_ids.h"
#include "toolchain/sem_ir/builtin_function_kind.h"
@@ -207,13 +208,25 @@ static auto BuildVtable(Context& context, Parse::ClassDefinitionId node_id,
auto override_fn_id =
context.insts().GetAs<SemIR::FunctionDecl>(*i).function_id;
implemented_impls.Insert(override_fn_id);
auto& override_fn = context.functions().Get(override_fn_id);
CheckFunctionTypeMatches(context, override_fn, fn, specific_id,
/*check_syntax=*/false,
/*check_self=*/false);
derived_vtable_entry_id = build_specific_function(*i);
override_fn.virtual_index = vtable.size();
CARBON_CHECK(override_fn.virtual_index == fn.virtual_index);
// TODO: When the base class is a C++ class, we could have multiple
// potential functions to override. Check against each of them rather
// than trying to override them all.
auto override_or_thunk_id =
BuildThunk(context, fn_id, specific_id, class_info.self_type_id, *i,
/*defer_definition=*/true);
if (override_or_thunk_id != SemIR::ErrorInst::InstId) {
auto override_or_thunk_fn_id =
context.insts()
.GetAs<SemIR::FunctionDecl>(override_or_thunk_id)
.function_id;
auto& override_or_thunk_fn =
context.functions().Get(override_or_thunk_fn_id);
derived_vtable_entry_id =
build_specific_function(override_or_thunk_id);
override_or_thunk_fn.virtual_index = vtable.size();
CARBON_CHECK(override_or_thunk_fn.virtual_index == fn.virtual_index);
}
} else if (auto base_vtable_specific_function =
context.insts().TryGetAs<SemIR::SpecificFunction>(
derived_vtable_entry_id)) {