Allow interop with templated but non-template functions. (#5809)

For example, this would allow using `std::string::size`, which is
templated because it's a member of the class template
`std::basic_string`, but isn't itself a function template.

toolchain/check/import_cpp.cpp

@@ -1073,7 +1073,8 @@ static auto ImportFunctionDecl(Context& context, SemIR::LocId loc_id,
     MarkFailedDecl(context, clang_decl);
     return SemIR::ErrorInst::InstId;
   }
-  if (clang_decl->getTemplatedKind() != clang::FunctionDecl::TK_NonTemplate) {
+  if (clang_decl->getTemplatedKind() ==
+      clang::FunctionDecl::TK_FunctionTemplate) {
     context.TODO(loc_id, "Unsupported: Template function");
     MarkFailedDecl(context, clang_decl);
     return SemIR::ErrorInst::InstId;

toolchain/check/testdata/interop/cpp/function/in_template.carbon

@@ -0,0 +1,94 @@
+// 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/in_template.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/in_template.carbon
+
+// --- class_template.h
+
+template<typename T> struct X {
+  static void f(T t);
+};
+
+// TODO: We should be able to instantiate the class when needed.
+template struct X<int>;
+
+using Y = X<int>;
+
+// --- use_class_template.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "class_template.h";
+
+fn F() {
+  //@dump-sem-ir-begin
+  Cpp.Y.f(42);
+  //@dump-sem-ir-end
+}
+
+// CHECK:STDOUT: --- use_class_template.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
+// CHECK:STDOUT:   %X: type = class_type @X [concrete]
+// CHECK:STDOUT:   %int_32: Core.IntLiteral = int_value 32 [concrete]
+// CHECK:STDOUT:   %i32: type = class_type @Int, @Int(%int_32) [concrete]
+// CHECK:STDOUT:   %f.type: type = fn_type @f [concrete]
+// CHECK:STDOUT:   %f: %f.type = struct_value () [concrete]
+// CHECK:STDOUT:   %int_42.20e: Core.IntLiteral = int_value 42 [concrete]
+// CHECK:STDOUT:   %ImplicitAs.type.205: type = facet_type <@ImplicitAs, @ImplicitAs(%i32)> [concrete]
+// CHECK:STDOUT:   %Convert.type.1b6: type = fn_type @Convert.1, @ImplicitAs(%i32) [concrete]
+// CHECK:STDOUT:   %To: Core.IntLiteral = bind_symbolic_name To, 0 [symbolic]
+// CHECK:STDOUT:   %Convert.type.0f9: type = fn_type @Convert.2, @ImplicitAs.impl.4f9(%To) [symbolic]
+// CHECK:STDOUT:   %Convert.f06: %Convert.type.0f9 = struct_value () [symbolic]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness.c75: <witness> = impl_witness imports.%ImplicitAs.impl_witness_table.a2f, @ImplicitAs.impl.4f9(%int_32) [concrete]
+// CHECK:STDOUT:   %Convert.type.035: type = fn_type @Convert.2, @ImplicitAs.impl.4f9(%int_32) [concrete]
+// CHECK:STDOUT:   %Convert.956: %Convert.type.035 = struct_value () [concrete]
+// CHECK:STDOUT:   %ImplicitAs.facet: %ImplicitAs.type.205 = facet_value Core.IntLiteral, (%ImplicitAs.impl_witness.c75) [concrete]
+// CHECK:STDOUT:   %.9c3: type = fn_type_with_self_type %Convert.type.1b6, %ImplicitAs.facet [concrete]
+// CHECK:STDOUT:   %Convert.bound: <bound method> = bound_method %int_42.20e, %Convert.956 [concrete]
+// CHECK:STDOUT:   %Convert.specific_fn: <specific function> = specific_function %Convert.956, @Convert.2(%int_32) [concrete]
+// CHECK:STDOUT:   %bound_method: <bound method> = bound_method %int_42.20e, %Convert.specific_fn [concrete]
+// CHECK:STDOUT:   %int_42.c68: %i32 = int_value 42 [concrete]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
+// CHECK:STDOUT:     .Y = %X.decl
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %X.decl: type = class_decl @X [concrete = constants.%X] {} {}
+// CHECK:STDOUT:   %f.decl: %f.type = fn_decl @f [concrete = constants.%f] {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import_ref.a5b: @ImplicitAs.impl.4f9.%Convert.type (%Convert.type.0f9) = import_ref Core//prelude/parts/int, loc16_39, loaded [symbolic = @ImplicitAs.impl.4f9.%Convert (constants.%Convert.f06)]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness_table.a2f = impl_witness_table (%Core.import_ref.a5b), @ImplicitAs.impl.4f9 [concrete]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %Y.ref: type = name_ref Y, imports.%X.decl [concrete = constants.%X]
+// CHECK:STDOUT:   %f.ref: %f.type = name_ref f, imports.%f.decl [concrete = constants.%f]
+// CHECK:STDOUT:   %int_42: Core.IntLiteral = int_value 42 [concrete = constants.%int_42.20e]
+// CHECK:STDOUT:   %impl.elem0: %.9c3 = impl_witness_access constants.%ImplicitAs.impl_witness.c75, element0 [concrete = constants.%Convert.956]
+// CHECK:STDOUT:   %bound_method.loc8_11.1: <bound method> = bound_method %int_42, %impl.elem0 [concrete = constants.%Convert.bound]
+// CHECK:STDOUT:   %specific_fn: <specific function> = specific_function %impl.elem0, @Convert.2(constants.%int_32) [concrete = constants.%Convert.specific_fn]
+// CHECK:STDOUT:   %bound_method.loc8_11.2: <bound method> = bound_method %int_42, %specific_fn [concrete = constants.%bound_method]
+// CHECK:STDOUT:   %int.convert_checked: init %i32 = call %bound_method.loc8_11.2(%int_42) [concrete = constants.%int_42.c68]
+// CHECK:STDOUT:   %.loc8_11.1: %i32 = value_of_initializer %int.convert_checked [concrete = constants.%int_42.c68]
+// CHECK:STDOUT:   %.loc8_11.2: %i32 = converted %int_42, %.loc8_11.1 [concrete = constants.%int_42.c68]
+// CHECK:STDOUT:   %f.call: init %empty_tuple.type = call %f.ref(%.loc8_11.2)
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT: }
+// CHECK:STDOUT:

toolchain/lower/testdata/interop/cpp/function_in_template.carbon

@@ -0,0 +1,73 @@
+// 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/lower/testdata/interop/cpp/function_in_template.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function_in_template.carbon
+
+// --- class_template.h
+
+template<typename T> struct X {
+  static void f(T t) {}
+};
+
+// TODO: We should be able to instantiate the class and function when needed.
+template struct X<int>;
+
+using Y = X<int>;
+
+// --- use_class_template.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "class_template.h";
+
+fn F() {
+  //@dump-sem-ir-begin
+  Cpp.Y.f(42);
+  //@dump-sem-ir-end
+}
+
+// CHECK:STDOUT: ; ModuleID = 'use_class_template.carbon'
+// CHECK:STDOUT: source_filename = "use_class_template.carbon"
+// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZN1XIiE1fEi = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: define void @_CF.Main() !dbg !7 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   call void @_ZN1XIiE1fEi(i32 42), !dbg !10
+// CHECK:STDOUT:   ret void, !dbg !11
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: mustprogress noinline nounwind optnone
+// CHECK:STDOUT: define weak_odr dso_local void @_ZN1XIiE1fEi(i32 %t) #0 comdat align 2 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %t.addr = alloca i32, align 4
+// CHECK:STDOUT:   store i32 %t, ptr %t.addr, align 4
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { mustprogress noinline nounwind optnone "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
+// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
+// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !6 = !DIFile(filename: "use_class_template.carbon", directory: "")
+// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !6, line: 6, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
+// CHECK:STDOUT: !9 = !{}
+// CHECK:STDOUT: !10 = !DILocation(line: 8, column: 3, scope: !7)
+// CHECK:STDOUT: !11 = !DILocation(line: 6, column: 1, scope: !7)