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adds checking support for CppUnsafeDeref witness (#6890)

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Iterators, smart pointers, optional, and expected types depend on
`operator*`. This commit adds `CppUnsafeDeref` as a core interface, with
an associated function, so that the compiler can dereference
user-defined C++ types.

Things not implemented in this commit:

* `operator*` overload resolution
* SemIR lowering

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>
This commit is contained in:
Christopher Di Bella
2026-03-12 18:02:34 +00:00
committed by GitHub
co-authored by Richard Smith
parent 1e9708e2cc
commit 4df2b6ea9d
8 changed files with 205 additions and 19 deletions
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toolchain/check/testdata/interop/cpp/deref.carbon
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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/full.carbon
//
// EXTRA-ARGS: --target=aarch64-unknown-linux --clang-arg=--std=c++20
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/deref.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/deref.carbon
// --- fail_todo_const_deref.carbon
library "[[@TEST_NAME]]";
import Cpp inline '''c++
class ConstDeref {
public:
auto operator*() const -> int&;
};
''';
fn TestDerefPass(var int_ptr: Cpp.ConstDeref) -> ref i32 {
// CHECK:STDERR: fail_todo_const_deref.carbon:[[@LINE+4]]:10: error: semantics TODO: `Unsupported definition of interface CppUnsafeDeref` [SemanticsTodo]
// CHECK:STDERR: return int_ptr.(Core.CppUnsafeDeref.Op)();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
return int_ptr.(Core.CppUnsafeDeref.Op)();
}
// --- fail_todo_mutable_deref.carbon
library "[[@TEST_NAME]]";
import Cpp inline '''c++
class MutableDeref {
public:
auto operator*() -> int&;
};
''';
fn TestDerefPass(var int_ptr: Cpp.MutableDeref) -> ref i32 {
// CHECK:STDERR: fail_todo_mutable_deref.carbon:[[@LINE+4]]:10: error: semantics TODO: `Unsupported definition of interface CppUnsafeDeref` [SemanticsTodo]
// CHECK:STDERR: return int_ptr.(Core.CppUnsafeDeref.Op)();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
return int_ptr.(Core.CppUnsafeDeref.Op)();
}
// --- fail_todo_multi_deref.carbon
library "[[@TEST_NAME]]";
import Cpp inline '''c++
class MultiDeref {
public:
auto operator*() & -> int&;
auto operator*() const& -> const int&;
auto operator*() && -> int&&;
auto operator*() const&& -> int const&&;
};
''';
fn TestDerefPass(var int_ptr: Cpp.MultiDeref) -> ref i32 {
// CHECK:STDERR: fail_todo_multi_deref.carbon:[[@LINE+4]]:10: error: semantics TODO: `operator* overload sets not implemented yet` [SemanticsTodo]
// CHECK:STDERR: return int_ptr.(Core.CppUnsafeDeref.Op)();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
return int_ptr.(Core.CppUnsafeDeref.Op)();
}
// --- fail_todo_maybe_deref.carbon
library "[[@TEST_NAME]]";
import Cpp inline '''c++
template<class T, class U>
concept SameImpl = __is_same(T, U);
template<class T, class U>
concept SameAs = SameImpl<T, U> && SameImpl<U, T>;
template<class T>
class MaybeDeref {
public:
auto operator*() const -> int&
requires SameAs<T, int>;
auto operator*() const -> const T&;
};
''';
fn TestDerefPass(var int_ptr: Cpp.MaybeDeref(i32)) -> ref i32 {
// CHECK:STDERR: fail_todo_maybe_deref.carbon:[[@LINE+4]]:10: error: semantics TODO: `operator* overload sets not implemented yet` [SemanticsTodo]
// CHECK:STDERR: return int_ptr.(Core.CppUnsafeDeref.Op)();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
return int_ptr.(Core.CppUnsafeDeref.Op)();
}
// --- fail_not_a_ptr.carbon
library "[[@TEST_NAME]]";
import Cpp inline '''c++
class NotAPtr {};
''';
fn TestDerefFail(not_ptr: Cpp.NotAPtr) {
// CHECK:STDERR: fail_not_a_ptr.carbon:[[@LINE+4]]:3: error: cannot access member of interface `Core.CppUnsafeDeref` in type `Cpp.NotAPtr` that does not implement that interface [MissingImplInMemberAccess]
// CHECK:STDERR: not_ptr.(Core.CppUnsafeDeref.Op)();
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
not_ptr.(Core.CppUnsafeDeref.Op)();
}