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Map Carbon value expressions to const-qualified C++ prvalues. (#6880)

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In C++ overload resolution, when mapping a Carbon value expression into
a C++ argument, produce a const-qualified argument where possible. This
has two effects:

* Overload resolution does not consider non-const-qualified member
functions to be viable for a prvalue self any more. This is desirable
since such functions are not actually callable with a prvalue self, and
permits overload resolution to pick a const-qualified overload instead.

* Overload resolution does not allow a Carbon value expression to be
passed to a C++ `T&&` parameter any more. This is desirable since it's
not correct to move from a value expression. Previously we allowed this
and moved from the value!
This commit is contained in:
Richard Smith
2026-03-11 03:42:19 +00:00
committed by GitHub
parent ba6257891e
commit 39fd358059
5 changed files with 164 additions and 166 deletions
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toolchain/check/testdata/interop/cpp/impls/implicit_as.carbon
Vendored
+9 -41
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@@ -92,10 +92,10 @@ import Cpp library "implicit_conversions.h";
fn NonConstConversionTest(s: Cpp.NonConstConversion) {
//@dump-sem-ir-begin
// CHECK:STDERR: fail_expr_category.carbon:[[@LINE+7]]:21: error: value expression passed to reference parameter [ValueForRefParam]
// CHECK:STDERR: fail_expr_category.carbon:[[@LINE+7]]:21: error: cannot implicitly convert expression of type `Cpp.NonConstConversion` to `Cpp.Dest` [ConversionFailure]
// CHECK:STDERR: let _: Cpp.Dest = s;
// CHECK:STDERR: ^
// CHECK:STDERR: fail_expr_category.carbon:[[@LINE+4]]:21: note: initializing function parameter [InCallToFunctionParam]
// CHECK:STDERR: fail_expr_category.carbon:[[@LINE+4]]:21: note: type `Cpp.NonConstConversion` does not implement interface `Core.ImplicitAs(Cpp.Dest)` [MissingImplInMemberAccessInContext]
// CHECK:STDERR: let _: Cpp.Dest = s;
// CHECK:STDERR: ^
// CHECK:STDERR:
@@ -568,18 +568,9 @@ fn InitFromStruct() {
// CHECK:STDOUT: --- fail_expr_category.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %NonConstConversion: type = class_type @NonConstConversion [concrete]
// CHECK:STDOUT: %pattern_type.b08: type = pattern_type %NonConstConversion [concrete]
// CHECK:STDOUT: %Dest: type = class_type @Dest [concrete]
// CHECK:STDOUT: %pattern_type.69a: type = pattern_type %Dest [concrete]
// CHECK:STDOUT: %NonConstConversion.cpp_operator.type: type = fn_type @NonConstConversion.cpp_operator [concrete]
// CHECK:STDOUT: %NonConstConversion.cpp_operator: %NonConstConversion.cpp_operator.type = struct_value () [concrete]
// CHECK:STDOUT: %ptr.551: type = ptr_type %Dest [concrete]
// CHECK:STDOUT: %Dest__carbon_thunk.type: type = fn_type @Dest__carbon_thunk [concrete]
// CHECK:STDOUT: %Dest__carbon_thunk: %Dest__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %Dest.cpp_destructor.type: type = fn_type @Dest.cpp_destructor [concrete]
// CHECK:STDOUT: %Dest.cpp_destructor: %Dest.cpp_destructor.type = struct_value () [concrete]
// CHECK:STDOUT: %Dest.5e7: type = class_type @Dest [concrete]
// CHECK:STDOUT: %pattern_type.69a: type = pattern_type %Dest.5e7 [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -589,21 +580,7 @@ fn InitFromStruct() {
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %NonConstConversion.decl: type = class_decl @NonConstConversion [concrete = constants.%NonConstConversion] {} {}
// CHECK:STDOUT: %Dest.decl: type = class_decl @Dest [concrete = constants.%Dest] {} {}
// CHECK:STDOUT: %NonConstConversion.cpp_operator.decl: %NonConstConversion.cpp_operator.type = fn_decl @NonConstConversion.cpp_operator [concrete = constants.%NonConstConversion.cpp_operator] {
// CHECK:STDOUT: %self.patt: %pattern_type.b08 = ref_binding_pattern self [concrete]
// CHECK:STDOUT: %self.param_patt: %pattern_type.b08 = ref_param_pattern %self.patt [concrete]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: %self.param: ref %NonConstConversion = ref_param call_param0
// CHECK:STDOUT: %self: ref %NonConstConversion = ref_binding self, %self.param
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %Dest__carbon_thunk.decl: %Dest__carbon_thunk.type = fn_decl @Dest__carbon_thunk [concrete = constants.%Dest__carbon_thunk] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %Dest.decl: type = class_decl @Dest [concrete = constants.%Dest.5e7] {} {}
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @NonConstConversionTest(%s.param: %NonConstConversion) {
@@ -612,21 +589,12 @@ fn InitFromStruct() {
// CHECK:STDOUT: %_.patt: %pattern_type.69a = value_binding_pattern _ [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %s.ref: %NonConstConversion = name_ref s, %s
// CHECK:STDOUT: %.loc15_13: type = splice_block %Dest.ref [concrete = constants.%Dest] {
// CHECK:STDOUT: %.loc15_13: type = splice_block %Dest.ref [concrete = constants.%Dest.5e7] {
// CHECK:STDOUT: %Cpp.ref.loc15: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %Dest.ref: type = name_ref Dest, imports.%Dest.decl [concrete = constants.%Dest]
// CHECK:STDOUT: %Dest.ref: type = name_ref Dest, imports.%Dest.decl [concrete = constants.%Dest.5e7]
// CHECK:STDOUT: }
// CHECK:STDOUT: %NonConstConversion.cpp_operator.bound: <bound method> = bound_method %s.ref, imports.%NonConstConversion.cpp_operator.decl
// CHECK:STDOUT: %.loc15_21.1: ref %Dest = temporary_storage
// CHECK:STDOUT: %addr: %ptr.551 = addr_of %.loc15_21.1
// CHECK:STDOUT: %Dest__carbon_thunk.call: init %empty_tuple.type = call imports.%Dest__carbon_thunk.decl(<error>, %addr)
// CHECK:STDOUT: %.loc15_21.2: init %Dest to %.loc15_21.1 = mark_in_place_init %Dest__carbon_thunk.call
// CHECK:STDOUT: %.loc15_21.3: init %Dest = converted %s.ref, %.loc15_21.2
// CHECK:STDOUT: %.loc15_21.4: ref %Dest = temporary %.loc15_21.1, %.loc15_21.3
// CHECK:STDOUT: %.loc15_21.5: %Dest = acquire_value %.loc15_21.4
// CHECK:STDOUT: %_: %Dest = value_binding _, %.loc15_21.5
// CHECK:STDOUT: %Dest.cpp_destructor.bound: <bound method> = bound_method %.loc15_21.4, constants.%Dest.cpp_destructor
// CHECK:STDOUT: %Dest.cpp_destructor.call: init %empty_tuple.type = call %Dest.cpp_destructor.bound(%.loc15_21.4)
// CHECK:STDOUT: %.loc15_21: %Dest.5e7 = converted %s.ref, <error> [concrete = <error>]
// CHECK:STDOUT: %_: %Dest.5e7 = value_binding _, <error> [concrete = <error>]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: