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carbon-lang/toolchain/check/testdata/interop/cpp/template/alias_template.carbon
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Chandler CarruthandChristopher Di Bella 8a59f2a76b Fix mangling collision for C++ class template specializations (#7269) 
Carbon-side thunks (for example the `Copy`/`Destroy` witness thunks
generated for imported C++ types) are mangled by Carbon, and their names
incorporate a fingerprint of the involved types. The instruction
fingerprinter identifies a class only by its name and parent scope,
which is sufficient for Carbon classes but not for imported C++ classes:
different specializations of one class template (and other cases such as
types in anonymous namespaces) share a Carbon name and parent scope. As
a result, the thunks for two distinct specializations could mangle to
the same name, producing a single LLVM function with two definitions and
failing `verifyModule` during lowering.

When fingerprinting a class imported from C++, also include the Clang
mangled name of its type.

Test: toolchain/lower/testdata/interop/cpp/thunks.carbon gains a split
with two specializations of one class template, each requiring a thunk;
their thunks now get distinct mangled names instead of colliding.

Assisted-by: Claude Code

---------

Co-authored-by: Christopher Di Bella <cjdb.ns@gmail.com>
2026-05-30 08:13:00 +00:00

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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/none.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/template/alias_template.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/template/alias_template.carbon
// --- alias_template.h
struct A {};
struct B {};
template<typename T, typename U> using First = T;
template<typename T, typename U> using Second = U;
// --- use_alias_template.carbon
library "[[@TEST_NAME]]";
import Cpp library "alias_template.h";
//@dump-sem-ir-begin
var a1: Cpp.First(Cpp.A, Cpp.B) = Cpp.A.A();
var b1: Cpp.First(Cpp.B, Cpp.A) = Cpp.B.B();
var b2: Cpp.Second(Cpp.A, Cpp.B) = Cpp.B.B();
var a2: Cpp.Second(Cpp.B, Cpp.A) = Cpp.A.A();
//@dump-sem-ir-end
// CHECK:STDOUT: --- use_alias_template.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %First.type: type = cpp_type_template_type First [concrete]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %First.template: %First.type = struct_value () [concrete]
// CHECK:STDOUT: %A: type = class_type @A [concrete]
// CHECK:STDOUT: %B: type = class_type @B [concrete]
// CHECK:STDOUT: %pattern_type.aa6: type = pattern_type %A [concrete]
// CHECK:STDOUT: %A.A.cpp_overload_set.type: type = cpp_overload_set_type @A.A.cpp_overload_set [concrete]
// CHECK:STDOUT: %A.A.cpp_overload_set.value: %A.A.cpp_overload_set.type = cpp_overload_set_value @A.A.cpp_overload_set [concrete]
// CHECK:STDOUT: %ptr.9f7: type = ptr_type %A [concrete]
// CHECK:STDOUT: %A__carbon_thunk.type: type = fn_type @A__carbon_thunk [concrete]
// CHECK:STDOUT: %A__carbon_thunk: %A__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %pattern_type.bbe: type = pattern_type %B [concrete]
// CHECK:STDOUT: %B.B.cpp_overload_set.type: type = cpp_overload_set_type @B.B.cpp_overload_set [concrete]
// CHECK:STDOUT: %B.B.cpp_overload_set.value: %B.B.cpp_overload_set.type = cpp_overload_set_value @B.B.cpp_overload_set [concrete]
// CHECK:STDOUT: %ptr.fab: type = ptr_type %B [concrete]
// CHECK:STDOUT: %B__carbon_thunk.type: type = fn_type @B__carbon_thunk [concrete]
// CHECK:STDOUT: %B__carbon_thunk: %B__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %Second.type: type = cpp_type_template_type Second [concrete]
// CHECK:STDOUT: %Second.template: %Second.type = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
// CHECK:STDOUT: .First = %First.template
// CHECK:STDOUT: .A = %A.decl
// CHECK:STDOUT: .B = %B.decl
// CHECK:STDOUT: .Second = %Second.template
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %First.template: %First.type = struct_value () [concrete = constants.%First.template]
// CHECK:STDOUT: %A.decl: type = class_decl @A [concrete = constants.%A] {} {}
// CHECK:STDOUT: %B.decl: type = class_decl @B [concrete = constants.%B] {} {}
// CHECK:STDOUT: %A.A.cpp_overload_set.value: %A.A.cpp_overload_set.type = cpp_overload_set_value @A.A.cpp_overload_set [concrete = constants.%A.A.cpp_overload_set.value]
// CHECK:STDOUT: %A__carbon_thunk.decl: %A__carbon_thunk.type = fn_decl @A__carbon_thunk [concrete = constants.%A__carbon_thunk] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %B.B.cpp_overload_set.value: %B.B.cpp_overload_set.type = cpp_overload_set_value @B.B.cpp_overload_set [concrete = constants.%B.B.cpp_overload_set.value]
// CHECK:STDOUT: %B__carbon_thunk.decl: %B__carbon_thunk.type = fn_decl @B__carbon_thunk [concrete = constants.%B__carbon_thunk] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %Second.template: %Second.type = struct_value () [concrete = constants.%Second.template]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %a1.patt: %pattern_type.aa6 = ref_binding_pattern a1 [concrete]
// CHECK:STDOUT: %a1.var_patt: %pattern_type.aa6 = var_pattern %a1.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %a1.var: ref %A = var %a1.var_patt [concrete]
// CHECK:STDOUT: %a1: ref %A = ref_binding a1, %a1.var [concrete = %a1.var]
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %b1.patt: %pattern_type.bbe = ref_binding_pattern b1 [concrete]
// CHECK:STDOUT: %b1.var_patt: %pattern_type.bbe = var_pattern %b1.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %b1.var: ref %B = var %b1.var_patt [concrete]
// CHECK:STDOUT: %b1: ref %B = ref_binding b1, %b1.var [concrete = %b1.var]
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %b2.patt: %pattern_type.bbe = ref_binding_pattern b2 [concrete]
// CHECK:STDOUT: %b2.var_patt: %pattern_type.bbe = var_pattern %b2.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %b2.var: ref %B = var %b2.var_patt [concrete]
// CHECK:STDOUT: %b2: ref %B = ref_binding b2, %b2.var [concrete = %b2.var]
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %a2.patt: %pattern_type.aa6 = ref_binding_pattern a2 [concrete]
// CHECK:STDOUT: %a2.var_patt: %pattern_type.aa6 = var_pattern %a2.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %a2.var: ref %A = var %a2.var_patt [concrete]
// CHECK:STDOUT: %a2: ref %A = ref_binding a2, %a2.var [concrete = %a2.var]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @__global_init() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %Cpp.ref.loc7: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %A.ref.loc7_38: type = name_ref A, imports.%A.decl [concrete = constants.%A]
// CHECK:STDOUT: %A.ref.loc7_40: %A.A.cpp_overload_set.type = name_ref A, imports.%A.A.cpp_overload_set.value [concrete = constants.%A.A.cpp_overload_set.value]
// CHECK:STDOUT: %.loc7_1: ref %A = splice_block file.%a1.var [concrete = file.%a1.var] {}
// CHECK:STDOUT: %addr.loc7: %ptr.9f7 = addr_of %.loc7_1
// CHECK:STDOUT: %A__carbon_thunk.call.loc7: init %empty_tuple.type = call imports.%A__carbon_thunk.decl(%addr.loc7)
// CHECK:STDOUT: %.loc7_43: init %A to %.loc7_1 = mark_in_place_init %A__carbon_thunk.call.loc7
// CHECK:STDOUT: assign file.%a1.var, %.loc7_43
// CHECK:STDOUT: %Cpp.ref.loc8: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %B.ref.loc8_38: type = name_ref B, imports.%B.decl [concrete = constants.%B]
// CHECK:STDOUT: %B.ref.loc8_40: %B.B.cpp_overload_set.type = name_ref B, imports.%B.B.cpp_overload_set.value [concrete = constants.%B.B.cpp_overload_set.value]
// CHECK:STDOUT: %.loc8_1: ref %B = splice_block file.%b1.var [concrete = file.%b1.var] {}
// CHECK:STDOUT: %addr.loc8: %ptr.fab = addr_of %.loc8_1
// CHECK:STDOUT: %B__carbon_thunk.call.loc8: init %empty_tuple.type = call imports.%B__carbon_thunk.decl(%addr.loc8)
// CHECK:STDOUT: %.loc8_43: init %B to %.loc8_1 = mark_in_place_init %B__carbon_thunk.call.loc8
// CHECK:STDOUT: assign file.%b1.var, %.loc8_43
// CHECK:STDOUT: %Cpp.ref.loc9: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %B.ref.loc9_39: type = name_ref B, imports.%B.decl [concrete = constants.%B]
// CHECK:STDOUT: %B.ref.loc9_41: %B.B.cpp_overload_set.type = name_ref B, imports.%B.B.cpp_overload_set.value [concrete = constants.%B.B.cpp_overload_set.value]
// CHECK:STDOUT: %.loc9_1: ref %B = splice_block file.%b2.var [concrete = file.%b2.var] {}
// CHECK:STDOUT: %addr.loc9: %ptr.fab = addr_of %.loc9_1
// CHECK:STDOUT: %B__carbon_thunk.call.loc9: init %empty_tuple.type = call imports.%B__carbon_thunk.decl(%addr.loc9)
// CHECK:STDOUT: %.loc9_44: init %B to %.loc9_1 = mark_in_place_init %B__carbon_thunk.call.loc9
// CHECK:STDOUT: assign file.%b2.var, %.loc9_44
// CHECK:STDOUT: %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %A.ref.loc10_39: type = name_ref A, imports.%A.decl [concrete = constants.%A]
// CHECK:STDOUT: %A.ref.loc10_41: %A.A.cpp_overload_set.type = name_ref A, imports.%A.A.cpp_overload_set.value [concrete = constants.%A.A.cpp_overload_set.value]
// CHECK:STDOUT: %.loc10_1: ref %A = splice_block file.%a2.var [concrete = file.%a2.var] {}
// CHECK:STDOUT: %addr.loc10: %ptr.9f7 = addr_of %.loc10_1
// CHECK:STDOUT: %A__carbon_thunk.call.loc10: init %empty_tuple.type = call imports.%A__carbon_thunk.decl(%addr.loc10)
// CHECK:STDOUT: %.loc10_44: init %A to %.loc10_1 = mark_in_place_init %A__carbon_thunk.call.loc10
// CHECK:STDOUT: assign file.%a2.var, %.loc10_44
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
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