Reverse Interop: Class declarations (#6955)

Generate class declarations for Carbon classes referenced from C++

Based on #6940, review from eb62070a01772ce28eaaa634fdaf80b724c57965
onwards

toolchain/check/cpp/generate_ast.cpp

@@ -25,8 +25,10 @@
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/raw_ostream.h"
+#include "toolchain/base/kind_switch.h"
 #include "toolchain/check/context.h"
 #include "toolchain/check/cpp/import.h"
+#include "toolchain/check/import_ref.h"
 #include "toolchain/check/name_lookup.h"
 #include "toolchain/diagnostics/diagnostic.h"
 #include "toolchain/diagnostics/emitter.h"
@@ -356,26 +358,40 @@ auto CarbonExternalASTSource::MapInstIdToClangDecl(
     clang::DeclContext& decl_context, LookupResult lookup)
     -> clang::NamedDecl* {
   auto target_inst_id = lookup.scope_result.target_inst_id();
-  if (auto target_inst =
-          context_->insts().TryGetAs<SemIR::Namespace>(target_inst_id)) {
-    auto& name_scope = context_->name_scopes().Get(target_inst->name_scope_id);
-    auto* identifier_info =
-        GetClangIdentifierInfo(*context_, name_scope.name_id());
-    // TODO: Don't immediately use the decl_context - build any intermediate
-    // namespaces iteratively.
-    // Eventually add a mapping and use that/populate it/keep it up to date.
-    // decl_context could be prepopulated in that mapping and not passed
-    // explicitly to MapInstIdToClangDecl.
-    auto* namespace_decl = clang::NamespaceDecl::Create(
-        *ast_context_, &decl_context, false, clang::SourceLocation(),
-        clang::SourceLocation(), identifier_info, nullptr, false);
-    auto result =
-        scope_map_.Insert(namespace_decl->getPrimaryContext(), target_inst_id);
-    CARBON_CHECK(result.is_inserted(), "Inserting over an existing entry.");
-    namespace_decl->setHasExternalVisibleStorage();
-    return namespace_decl;
+  auto target_constant =
+      context_->constant_values().GetConstantInstId(target_inst_id);
+  auto target_inst = context_->insts().Get(target_constant);
+  CARBON_KIND_SWITCH(target_inst) {
+    case CARBON_KIND(SemIR::Namespace namespace_info): {
+      auto& name_scope =
+          context_->name_scopes().Get(namespace_info.name_scope_id);
+      auto* identifier_info =
+          GetClangIdentifierInfo(*context_, name_scope.name_id());
+      // TODO: Don't immediately use the decl_context - build any intermediate
+      // namespaces iteratively.
+      // Eventually add a mapping and use that/populate it/keep it up to date.
+      // decl_context could be prepopulated in that mapping and not passed
+      // explicitly to MapInstIdToClangDecl.
+      auto* namespace_decl = clang::NamespaceDecl::Create(
+          *ast_context_, &decl_context, false, clang::SourceLocation(),
+          clang::SourceLocation(), identifier_info, nullptr, false);
+      auto result = scope_map_.Insert(namespace_decl->getPrimaryContext(),
+                                      target_inst_id);
+      CARBON_CHECK(result.is_inserted(), "Inserting over an existing entry.");
+      namespace_decl->setHasExternalVisibleStorage();
+      return namespace_decl;
+    }
+    case CARBON_KIND(SemIR::ClassType class_type): {
+      const auto& class_info = context_->classes().Get(class_type.class_id);
+      auto* identifier_info =
+          GetClangIdentifierInfo(*context_, class_info.name_id);
+      return clang::CXXRecordDecl::Create(
+          *ast_context_, clang::TagTypeKind::Class, &decl_context,
+          clang::SourceLocation(), clang::SourceLocation(), identifier_info);
+    }
+    default:
+      return nullptr;
   }
-  return nullptr;
 }
 
 auto CarbonExternalASTSource::FindExternalVisibleDeclsByName(

toolchain/check/testdata/interop/cpp/reverse/simple.carbon

@@ -14,6 +14,8 @@
 package Other;
 namespace Nested;
 namespace Nested.Again;
+
+class Class1;
 // --- namespace.carbon
 
 library "[[@TEST_NAME]]";
@@ -23,4 +25,14 @@ import Cpp inline '''
 namespace X = Carbon::Other;
 namespace Y = Carbon::Other::Nested;
 namespace Z = Carbon::Other::Nested::Again;
+Carbon::Other::Class1 *glbl;
+
+template<typename T> void f1() {
+  T* v;
+}
+
+void f2() {
+  f1<Carbon::Other::Class1>();
+}
+
 ''';

toolchain/lower/testdata/interop/cpp/reverse/mangle_type.carbon

@@ -0,0 +1,71 @@
+// 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/lower/testdata/interop/cpp/reverse/mangle_type.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/reverse/mangle_type.carbon
+
+// --- other.carbon
+package Other;
+
+class Class1;
+// --- namespace.carbon
+
+library "[[@TEST_NAME]]";
+
+import Other;
+import Cpp inline '''
+
+void f1(Carbon::Other::Class1*) {
+}
+
+''';
+
+// CHECK:STDOUT: ; ModuleID = 'other.carbon'
+// CHECK:STDOUT: source_filename = "other.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "other.carbon", directory: "")
+// CHECK:STDOUT: ; ModuleID = 'namespace.carbon'
+// CHECK:STDOUT: source_filename = "namespace.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: ; Function Attrs: mustprogress nounwind uwtable
+// CHECK:STDOUT: define dso_local void @_Z2f1PN6Carbon5Other6Class1E(ptr noundef %0) #0 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.addr = alloca ptr, align 8
+// CHECK:STDOUT:   store ptr %0, ptr %.addr, align 8, !tbaa !11
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { mustprogress nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "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: !llvm.errno.tbaa = !{!7}
+// 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 8, !"PIC Level", i32 2}
+// CHECK:STDOUT: !3 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !4 = !{i32 7, !"uwtable", i32 2}
+// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !6 = !DIFile(filename: "namespace.carbon", directory: "")
+// CHECK:STDOUT: !7 = !{!8, !8, i64 0}
+// CHECK:STDOUT: !8 = !{!"int", !9, i64 0}
+// CHECK:STDOUT: !9 = !{!"omnipotent char", !10, i64 0}
+// CHECK:STDOUT: !10 = !{!"Simple C++ TBAA"}
+// CHECK:STDOUT: !11 = !{!12, !12, i64 0}
+// CHECK:STDOUT: !12 = !{!"p1 _ZTSN6Carbon5Other6Class1E", !13, i64 0}
+// CHECK:STDOUT: !13 = !{!"any pointer", !9, i64 0}