From 352d1f8fb2c3d2013033133b42714a6be9683e20 Mon Sep 17 00:00:00 2001
From: Christian Blichmann <cblichmann@google.com>
Date: Mon, 14 Aug 2023 06:13:51 -0700
Subject: [PATCH] Clang tool: Emit aggregates with default initialized members

PiperOrigin-RevId: 556765694
Change-Id: I2547919cdc1fcb048c99de325a8b2c24800b0e06
---
 .../tools/clang_generator/emitter.cc          | 18 +++++--
 .../tools/clang_generator/emitter_test.cc     | 47 +++++++++++++++++++
 2 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/sandboxed_api/tools/clang_generator/emitter.cc b/sandboxed_api/tools/clang_generator/emitter.cc
index 99b962e..0066f95 100644
--- a/sandboxed_api/tools/clang_generator/emitter.cc
+++ b/sandboxed_api/tools/clang_generator/emitter.cc
@@ -247,12 +247,20 @@ std::string GetSpelling(const clang::Decl* decl) {
   }
 
   if (const auto* record_decl = llvm::dyn_cast<clang::CXXRecordDecl>(decl)) {
-    if (!record_decl->isCLike()) {
-      // For C++ classes/structs, only emit a forward declaration.
-      return absl::StrCat(PrintRecordTemplateArguments(record_decl),
-                          record_decl->isClass() ? "class " : "struct ",
-                          ToStringView(record_decl->getName()));
+    if (record_decl->hasDefinition() &&
+        // Aggregates capture all C-like structs, but also structs with
+        // non-static members that have default initializers.
+        record_decl->isAggregate() &&
+        // Make sure to skip types with user-defined methods (including
+        // constructors).
+        record_decl->methods().empty()) {
+      return PrintDecl(decl);
     }
+    // For unsupported types or types with no definition, only emit a forward
+    // declaration.
+    return absl::StrCat(PrintRecordTemplateArguments(record_decl),
+                        record_decl->isClass() ? "class " : "struct ",
+                        ToStringView(record_decl->getName()));
   }
   return PrintDecl(decl);
 }
diff --git a/sandboxed_api/tools/clang_generator/emitter_test.cc b/sandboxed_api/tools/clang_generator/emitter_test.cc
index 332e947..cdfb8ba 100644
--- a/sandboxed_api/tools/clang_generator/emitter_test.cc
+++ b/sandboxed_api/tools/clang_generator/emitter_test.cc
@@ -201,6 +201,53 @@ TEST_F(EmitterTest, ParentNotCollected) {
                           " int data; }"));
 }
 
+TEST_F(EmitterTest, StructForwardDecl) {
+  EmitterForTesting emitter;
+  ASSERT_THAT(
+      RunFrontendAction(
+          R"(struct A;
+             extern "C" void UsingForwardDeclaredStruct(A* s);)",
+          std::make_unique<GeneratorAction>(emitter, GeneratorOptions())),
+      IsOk());
+
+  EXPECT_THAT(UglifyAll(emitter.SpellingsForNS("")), ElementsAre("struct A"));
+}
+
+TEST_F(EmitterTest, AggregateStructWithDefaultedMembers) {
+  EmitterForTesting emitter;
+  ASSERT_THAT(
+      RunFrontendAction(
+          R"(struct A {
+               int a = 0;
+               int b = 42;
+             };
+             extern "C" void AggregateStruct(A* s);)",
+          std::make_unique<GeneratorAction>(emitter, GeneratorOptions())),
+      IsOk());
+
+  EXPECT_THAT(UglifyAll(emitter.SpellingsForNS("")),
+              ElementsAre("struct A {"
+                          " int a = 0;"
+                          " int b = 42; }"));
+}
+
+TEST_F(EmitterTest, AggregateStructWithMethods) {
+  EmitterForTesting emitter;
+  ASSERT_THAT(
+      RunFrontendAction(
+          R"(struct A {
+               int a = 0;
+               int b = 42;
+               int my_mem_fn();
+             };
+             extern "C" void AggregateStruct(A* s);)",
+          std::make_unique<GeneratorAction>(emitter, GeneratorOptions())),
+      IsOk());
+
+  // Expect a forward decl in this case
+  EXPECT_THAT(UglifyAll(emitter.SpellingsForNS("")), ElementsAre("struct A"));
+}
+
 TEST_F(EmitterTest, RemoveQualifiers) {
   EmitterForTesting emitter;
   ASSERT_THAT(