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carbon-lang/toolchain/check/testdata/interop/cpp/function/decayed_param.carbon
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Dana Jansens e682a6660d Avoid adding extraneous local instructions while importing witness table entries (#6180) 
When deducing arguments for generic parameters of an `impl`, the
deduction calls `Convert` on the input arguments. Often, the input
argument is a facet, and needs to be converted to a type via
FacetAccessType in order to produce a different facet. These
instructions end up being added to the semir, but only their constant
values are needed for the resulting specific returned from Deduce.

In the best case, these extra instructions are just noise in the semir,
or they just cause instruction names to get differentiated with larger
suffixes.

In the worst case, these extra instructions contain references to
instructions from a generic context, and leak them out of that generic
context and into another. In particular, when importing a
LookupImplWitness instruction, the re-evaluation of it can do deduce
(when the lookup is against a generic `impl`). The instructions created
in Deduce are not part of the import, and end up referring to imported
instructions from the local context, which leads to confusion in the
toolchain, and can crash.

The `import_self_specific.carbon` test demonstrates this. It causes the
`I.F` function to be imported from the `I` interface when building the
witness table for the `impl`. Doing so imports the specific of `C` which
includes a LookupImplWitness for `Self.Accoc` in `I`. The `Self` is a
BindSymbolicName with generic binding index 0, in `I`. When Convert
creates instructions in the generic `impl forall D`, however, they end
up referencing and including this BindSymbolicName into its eval block.
But the generic binding 0 in the `impl` is a very different thing (a
value of type `E`). This confusion leads to crashes.
2025-10-09 16:07:30 +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/int.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/function/decayed_param.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/decayed_param.carbon
// --- params.h
void TakesArray(int arr[42]);
void TakesFunction(int f(int));
int Function(int);
// --- fail_todo_call_params.carbon
library "[[@TEST_NAME]]";
import Cpp library "params.h";
fn G(n: i32) -> i32;
fn F() {
//@dump-sem-ir-begin
var n: array(i32, 42);
// CHECK:STDERR: fail_todo_call_params.carbon:[[@LINE+4]]:3: error: semantics TODO: `Unsupported: parameter type: int *` [SemanticsTodo]
// CHECK:STDERR: Cpp.TakesArray(&n[0]);
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
Cpp.TakesArray(&n[0]);
// CHECK:STDERR: fail_todo_call_params.carbon:[[@LINE+4]]:18: error: member name `nullptr` not found in `Cpp` [MemberNameNotFoundInInstScope]
// CHECK:STDERR: Cpp.TakesArray(Cpp.nullptr);
// CHECK:STDERR: ^~~~~~~~~~~
// CHECK:STDERR:
Cpp.TakesArray(Cpp.nullptr);
// CHECK:STDERR: fail_todo_call_params.carbon:[[@LINE+4]]:21: error: call argument of type `<type of G>` is not supported [CppCallArgTypeNotSupported]
// CHECK:STDERR: Cpp.TakesFunction(G);
// CHECK:STDERR: ^
// CHECK:STDERR:
Cpp.TakesFunction(G);
// CHECK:STDERR: fail_todo_call_params.carbon:[[@LINE+4]]:21: error: call argument of type `<type of Cpp.Function>` is not supported [CppCallArgTypeNotSupported]
// CHECK:STDERR: Cpp.TakesFunction(Cpp.Function);
// CHECK:STDERR: ^~~~~~~~~~~~
// CHECK:STDERR:
Cpp.TakesFunction(Cpp.Function);
// CHECK:STDERR: fail_todo_call_params.carbon:[[@LINE+8]]:26: error: no matching function for call to 'TakesFunction' [CppInteropParseError]
// CHECK:STDERR: 43 | Cpp.TakesFunction(&n[0]);
// CHECK:STDERR: | ^
// CHECK:STDERR: fail_todo_call_params.carbon:[[@LINE-34]]:10: in file included here [InCppInclude]
// CHECK:STDERR: ./params.h:3:6: note: candidate function not viable: no known conversion from 'int * _Nonnull' to 'int (*)(int)' for 1st argument [CppInteropParseNote]
// CHECK:STDERR: 3 | void TakesFunction(int f(int));
// CHECK:STDERR: | ^ ~~~~~~~~~~
// CHECK:STDERR:
Cpp.TakesFunction(&n[0]);
// CHECK:STDERR: fail_todo_call_params.carbon:[[@LINE+4]]:21: error: member name `nullptr` not found in `Cpp` [MemberNameNotFoundInInstScope]
// CHECK:STDERR: Cpp.TakesFunction(Cpp.nullptr);
// CHECK:STDERR: ^~~~~~~~~~~
// CHECK:STDERR:
Cpp.TakesFunction(Cpp.nullptr);
//@dump-sem-ir-end
}
// CHECK:STDOUT: --- fail_todo_call_params.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %int_32: Core.IntLiteral = int_value 32 [concrete]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %i32: type = class_type @Int, @Int(%int_32) [concrete]
// CHECK:STDOUT: %G.type: type = fn_type @G [concrete]
// CHECK:STDOUT: %G: %G.type = struct_value () [concrete]
// CHECK:STDOUT: %int_42: Core.IntLiteral = int_value 42 [concrete]
// CHECK:STDOUT: %array_type: type = array_type %int_42, %i32 [concrete]
// CHECK:STDOUT: %ptr.830: type = ptr_type %array_type [concrete]
// CHECK:STDOUT: %pattern_type.b6e: type = pattern_type %array_type [concrete]
// CHECK:STDOUT: %TakesArray.cpp_overload_set.type: type = cpp_overload_set_type @TakesArray.cpp_overload_set [concrete]
// CHECK:STDOUT: %TakesArray.cpp_overload_set.value: %TakesArray.cpp_overload_set.type = cpp_overload_set_value @TakesArray.cpp_overload_set [concrete]
// CHECK:STDOUT: %int_0.5c6: Core.IntLiteral = int_value 0 [concrete]
// CHECK:STDOUT: %ImplicitAs.type.d14: type = facet_type <@ImplicitAs, @ImplicitAs(%i32)> [concrete]
// CHECK:STDOUT: %ImplicitAs.Convert.type.1b6: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%i32) [concrete]
// CHECK:STDOUT: %To: Core.IntLiteral = bind_symbolic_name To, 0 [symbolic]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.340: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%To) [symbolic]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.1c0: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.340 = struct_value () [symbolic]
// CHECK:STDOUT: %ImplicitAs.impl_witness.204: <witness> = impl_witness imports.%ImplicitAs.impl_witness_table.9e9, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.584: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.584 = struct_value () [concrete]
// CHECK:STDOUT: %ImplicitAs.facet: %ImplicitAs.type.d14 = facet_value Core.IntLiteral, (%ImplicitAs.impl_witness.204) [concrete]
// CHECK:STDOUT: %.1df: type = fn_type_with_self_type %ImplicitAs.Convert.type.1b6, %ImplicitAs.facet [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.bound: <bound method> = bound_method %int_0.5c6, %Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0 [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn: <specific function> = specific_function %Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0, @Core.IntLiteral.as.ImplicitAs.impl.Convert(%int_32) [concrete]
// CHECK:STDOUT: %bound_method: <bound method> = bound_method %int_0.5c6, %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn [concrete]
// CHECK:STDOUT: %int_0.6a9: %i32 = int_value 0 [concrete]
// CHECK:STDOUT: %ptr.235: type = ptr_type %i32 [concrete]
// CHECK:STDOUT: %TakesFunction.cpp_overload_set.type: type = cpp_overload_set_type @TakesFunction.cpp_overload_set [concrete]
// CHECK:STDOUT: %TakesFunction.cpp_overload_set.value: %TakesFunction.cpp_overload_set.type = cpp_overload_set_value @TakesFunction.cpp_overload_set [concrete]
// CHECK:STDOUT: %Function.cpp_overload_set.type: type = cpp_overload_set_type @Function.cpp_overload_set [concrete]
// CHECK:STDOUT: %Function.cpp_overload_set.value: %Function.cpp_overload_set.type = cpp_overload_set_value @Function.cpp_overload_set [concrete]
// CHECK:STDOUT: %type_where: type = facet_type <type where .Self impls <CanDestroy>> [concrete]
// CHECK:STDOUT: %facet_value: %type_where = facet_value %array_type, () [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.4f7: type = fn_type @DestroyT.binding.as_type.as.Destroy.impl.Op, @DestroyT.binding.as_type.as.Destroy.impl(%facet_value) [concrete]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.ce8: %DestroyT.binding.as_type.as.Destroy.impl.Op.type.4f7 = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
// CHECK:STDOUT: .TakesArray = %TakesArray.cpp_overload_set.value
// CHECK:STDOUT: .nullptr = <poisoned>
// CHECK:STDOUT: .TakesFunction = %TakesFunction.cpp_overload_set.value
// CHECK:STDOUT: .Function = %Function.cpp_overload_set.value
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %TakesArray.cpp_overload_set.value: %TakesArray.cpp_overload_set.type = cpp_overload_set_value @TakesArray.cpp_overload_set [concrete = constants.%TakesArray.cpp_overload_set.value]
// CHECK:STDOUT: %Core.import_ref.ee7: @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert.type (%Core.IntLiteral.as.ImplicitAs.impl.Convert.type.340) = import_ref Core//prelude/parts/int, loc{{\d+_\d+}}, loaded [symbolic = @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert (constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.1c0)]
// CHECK:STDOUT: %ImplicitAs.impl_witness_table.9e9 = impl_witness_table (%Core.import_ref.ee7), @Core.IntLiteral.as.ImplicitAs.impl [concrete]
// CHECK:STDOUT: %TakesFunction.cpp_overload_set.value: %TakesFunction.cpp_overload_set.type = cpp_overload_set_value @TakesFunction.cpp_overload_set [concrete = constants.%TakesFunction.cpp_overload_set.value]
// CHECK:STDOUT: %Function.cpp_overload_set.value: %Function.cpp_overload_set.type = cpp_overload_set_value @Function.cpp_overload_set [concrete = constants.%Function.cpp_overload_set.value]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @F() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %n.patt: %pattern_type.b6e = binding_pattern n [concrete]
// CHECK:STDOUT: %n.var_patt: %pattern_type.b6e = var_pattern %n.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %n.var: ref %array_type = var %n.var_patt
// CHECK:STDOUT: %.loc10: type = splice_block %array_type [concrete = constants.%array_type] {
// CHECK:STDOUT: %int_32.loc10: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
// CHECK:STDOUT: %i32.loc10: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
// CHECK:STDOUT: %int_42: Core.IntLiteral = int_value 42 [concrete = constants.%int_42]
// CHECK:STDOUT: %array_type: type = array_type %int_42, %i32.loc10 [concrete = constants.%array_type]
// CHECK:STDOUT: }
// CHECK:STDOUT: %n: ref %array_type = bind_name n, %n.var
// CHECK:STDOUT: %Cpp.ref.loc15: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %TakesArray.ref.loc15: %TakesArray.cpp_overload_set.type = name_ref TakesArray, imports.%TakesArray.cpp_overload_set.value [concrete = constants.%TakesArray.cpp_overload_set.value]
// CHECK:STDOUT: %n.ref.loc15: ref %array_type = name_ref n, %n
// CHECK:STDOUT: %int_0.loc15: Core.IntLiteral = int_value 0 [concrete = constants.%int_0.5c6]
// CHECK:STDOUT: %int_32.loc15: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
// CHECK:STDOUT: %i32.loc15: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
// CHECK:STDOUT: %impl.elem0.loc15: %.1df = impl_witness_access constants.%ImplicitAs.impl_witness.204, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0]
// CHECK:STDOUT: %bound_method.loc15_21.1: <bound method> = bound_method %int_0.loc15, %impl.elem0.loc15 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound]
// CHECK:STDOUT: %specific_fn.loc15: <specific function> = specific_function %impl.elem0.loc15, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
// CHECK:STDOUT: %bound_method.loc15_21.2: <bound method> = bound_method %int_0.loc15, %specific_fn.loc15 [concrete = constants.%bound_method]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc15: init %i32 = call %bound_method.loc15_21.2(%int_0.loc15) [concrete = constants.%int_0.6a9]
// CHECK:STDOUT: %.loc15_21.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc15 [concrete = constants.%int_0.6a9]
// CHECK:STDOUT: %.loc15_21.2: %i32 = converted %int_0.loc15, %.loc15_21.1 [concrete = constants.%int_0.6a9]
// CHECK:STDOUT: %.loc15_22: ref %i32 = array_index %n.ref.loc15, %.loc15_21.2
// CHECK:STDOUT: %addr.loc15: %ptr.235 = addr_of %.loc15_22
// CHECK:STDOUT: %Cpp.ref.loc21_3: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %TakesArray.ref.loc21: %TakesArray.cpp_overload_set.type = name_ref TakesArray, imports.%TakesArray.cpp_overload_set.value [concrete = constants.%TakesArray.cpp_overload_set.value]
// CHECK:STDOUT: %Cpp.ref.loc21_18: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %nullptr.ref.loc21: <error> = name_ref nullptr, <error> [concrete = <error>]
// CHECK:STDOUT: %Cpp.ref.loc27: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %TakesFunction.ref.loc27: %TakesFunction.cpp_overload_set.type = name_ref TakesFunction, imports.%TakesFunction.cpp_overload_set.value [concrete = constants.%TakesFunction.cpp_overload_set.value]
// CHECK:STDOUT: %G.ref: %G.type = name_ref G, file.%G.decl [concrete = constants.%G]
// CHECK:STDOUT: %Cpp.ref.loc33_3: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %TakesFunction.ref.loc33: %TakesFunction.cpp_overload_set.type = name_ref TakesFunction, imports.%TakesFunction.cpp_overload_set.value [concrete = constants.%TakesFunction.cpp_overload_set.value]
// CHECK:STDOUT: %Cpp.ref.loc33_21: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %Function.ref: %Function.cpp_overload_set.type = name_ref Function, imports.%Function.cpp_overload_set.value [concrete = constants.%Function.cpp_overload_set.value]
// CHECK:STDOUT: %Cpp.ref.loc43: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %TakesFunction.ref.loc43: %TakesFunction.cpp_overload_set.type = name_ref TakesFunction, imports.%TakesFunction.cpp_overload_set.value [concrete = constants.%TakesFunction.cpp_overload_set.value]
// CHECK:STDOUT: %n.ref.loc43: ref %array_type = name_ref n, %n
// CHECK:STDOUT: %int_0.loc43: Core.IntLiteral = int_value 0 [concrete = constants.%int_0.5c6]
// CHECK:STDOUT: %int_32.loc43: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
// CHECK:STDOUT: %i32.loc43: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
// CHECK:STDOUT: %impl.elem0.loc43: %.1df = impl_witness_access constants.%ImplicitAs.impl_witness.204, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0]
// CHECK:STDOUT: %bound_method.loc43_24.1: <bound method> = bound_method %int_0.loc43, %impl.elem0.loc43 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound]
// CHECK:STDOUT: %specific_fn.loc43: <specific function> = specific_function %impl.elem0.loc43, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
// CHECK:STDOUT: %bound_method.loc43_24.2: <bound method> = bound_method %int_0.loc43, %specific_fn.loc43 [concrete = constants.%bound_method]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc43: init %i32 = call %bound_method.loc43_24.2(%int_0.loc43) [concrete = constants.%int_0.6a9]
// CHECK:STDOUT: %.loc43_24.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc43 [concrete = constants.%int_0.6a9]
// CHECK:STDOUT: %.loc43_24.2: %i32 = converted %int_0.loc43, %.loc43_24.1 [concrete = constants.%int_0.6a9]
// CHECK:STDOUT: %.loc43_25: ref %i32 = array_index %n.ref.loc43, %.loc43_24.2
// CHECK:STDOUT: %addr.loc43: %ptr.235 = addr_of %.loc43_25
// CHECK:STDOUT: %Cpp.ref.loc49_3: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %TakesFunction.ref.loc49: %TakesFunction.cpp_overload_set.type = name_ref TakesFunction, imports.%TakesFunction.cpp_overload_set.value [concrete = constants.%TakesFunction.cpp_overload_set.value]
// CHECK:STDOUT: %Cpp.ref.loc49_21: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %nullptr.ref.loc49: <error> = name_ref nullptr, <error> [concrete = <error>]
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.bound: <bound method> = bound_method %n.var, constants.%DestroyT.binding.as_type.as.Destroy.impl.Op.ce8
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %bound_method.loc10: <bound method> = bound_method %n.var, %DestroyT.binding.as_type.as.Destroy.impl.Op.specific_fn
// CHECK:STDOUT: %addr.loc10: %ptr.830 = addr_of %n.var
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.call: init %empty_tuple.type = call %bound_method.loc10(%addr.loc10)
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
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