Codegen for safe union

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -753,6 +753,11 @@ void Converter::EmitRustStructOrUnion(clang::RecordDecl *decl) {
     }
   }
 
+  if (decl->isUnion()) {
+    EmitRustUnion(decl);
+    return;
+  }
+
   // Derived traits
   if (EmitsReprCForRecords()) {
     StrCat("#[repr(C)]");
@@ -770,8 +775,7 @@ void Converter::EmitRustStructOrUnion(clang::RecordDecl *decl) {
   auto access = clang::dyn_cast<clang::CXXRecordDecl>(decl)
                     ? AccessSpecifierAsString(decl->getAccess())
                     : keyword::kPub;
-  StrCat(access, decl->isUnion() ? keyword::kUnion : keyword::kStruct,
-         GetRecordName(decl));
+  StrCat(access, keyword::kStruct, GetRecordName(decl));
   {
     PushBrace brace(*this);
     for (auto *field : decl->fields()) {
@@ -817,6 +821,31 @@ void Converter::EmitRustStructOrUnion(clang::RecordDecl *decl) {
   AddByteReprTrait(decl);
 }
 
+void Converter::EmitRustUnion(clang::RecordDecl *decl) {
+  if (EmitsReprCForRecords()) {
+    StrCat("#[repr(C)]");
+  }
+  auto attrs = GetStructAttributes(decl);
+  Mapper::SetDerives(ctx_.getCanonicalTagType(decl),
+                     std::vector<std::string>(attrs.begin(), attrs.end()));
+  StrCat("#[derive(");
+  for (auto *attr : attrs) {
+    StrCat(attr, ',');
+  }
+  StrCat(")]");
+
+  StrCat(keyword::kPub, keyword::kUnion, GetRecordName(decl));
+  {
+    PushBrace brace(*this);
+    for (auto *field : decl->fields()) {
+      VisitFieldDecl(field);
+    }
+  }
+
+  AddDefaultTrait(decl);
+  AddByteReprTrait(decl);
+}
+
 bool Converter::VisitCXXRecordDecl(clang::CXXRecordDecl *decl) {
   if (clang::isa<clang::ClassTemplateSpecializationDecl>(decl)) {
     materializeTemplateSpecialization(decl);

cpp2rust/converter/converter.h

@@ -112,6 +112,8 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
   virtual void EmitRustStructOrUnion(clang::RecordDecl *decl);
 
+  virtual void EmitRustUnion(clang::RecordDecl *decl);
+
   virtual bool EmitsReprCForRecords() const { return true; }
 
   virtual bool VisitCXXMethodDecl(clang::CXXMethodDecl *decl);

cpp2rust/converter/models/converter_refcount.cpp

@@ -469,6 +469,42 @@ void ConverterRefCount::AddDefaultTrait(const clang::RecordDecl *decl) {
 }
 
 void ConverterRefCount::AddDefaultTraitForUnion(const clang::RecordDecl *decl) {
+  auto name = GetRecordName(decl);
+  StrCat(std::format("impl Default for {}", name));
+  PushBrace impl_brace(*this);
+  StrCat("fn default() -> Self");
+  PushBrace fn_brace(*this);
+  StrCat(std::format("{} {{ __store: libcc2rs::UnionStore::new({}) }}", name,
+                     ctx_.getASTRecordLayout(decl).getSize().getQuantity()));
+}
+
+void ConverterRefCount::EmitRustUnion(clang::RecordDecl *decl) {
+  auto name = GetRecordName(decl);
+
+  auto attrs = GetStructAttributes(decl);
+  Mapper::SetDerives(ctx_.getCanonicalTagType(decl),
+                     std::vector<std::string>(attrs.begin(), attrs.end()));
+  StrCat("#[derive(");
+  for (auto *attr : attrs) {
+    StrCat(attr, ',');
+  }
+  StrCat(")]");
+
+  StrCat(
+      std::format("pub struct {} {{ __store: libcc2rs::UnionStore, }}", name));
+
+  StrCat(std::format("impl {}", name));
+  {
+    PushBrace impl_brace(*this);
+    for (auto *field : decl->fields()) {
+      StrCat(std::format(
+          "pub fn {}(&self) -> Ptr<{}> {{ self.__store.pod(0) }}",
+          GetNamedDeclAsString(field), Mapper::Map(field->getType())));
+    }
+  }
+
+  AddDefaultTrait(decl);
+  AddByteReprTrait(decl);
 }
 
 void ConverterRefCount::AddDropTrait(const clang::CXXRecordDecl *decl) {
@@ -1789,6 +1825,11 @@ std::vector<const char *>
 ConverterRefCount::GetStructAttributes(const clang::RecordDecl *decl) {
   std::vector<const char *> attrs;
 
+  if (decl->isUnion()) {
+    attrs.emplace_back("Clone");
+    return attrs;
+  }
+
   if (RecordDerivesDefault(decl)) {
     attrs.emplace_back("Default");
   }

cpp2rust/converter/models/converter_refcount.h

@@ -28,6 +28,8 @@ class ConverterRefCount final : public Converter {
 
   bool VisitCXXRecordDecl(clang::CXXRecordDecl *decl) override;
 
+  void EmitRustUnion(clang::RecordDecl *decl) override;
+
   bool EmitsReprCForRecords() const override { return false; }
 
   void ConvertOrdAndPartialOrdTraits(const clang::CXXRecordDecl *decl,