Add ByteRepr for unions (#212)

Author: lucic71

cpp2rust/converter/converter_lib.cpp

@@ -213,7 +213,7 @@ bool TypeImplementsByteRepr(clang::QualType qt) {
       return false;
     }
     if (rd->isUnion()) {
-      return false;
+      return true;
     }
     for (const auto *field : rd->fields()) {
       if (!TypeImplementsByteRepr(field->getType())) {

cpp2rust/converter/models/converter_refcount.cpp

@@ -554,9 +554,20 @@ void ConverterRefCount::AddByteReprTrait(const clang::RecordDecl *decl) {
     return;
   }
 
-  StrCat(std::format("impl ByteRepr for {}", struct_name));
+  StrCat("impl ByteRepr for ", struct_name);
   PushBrace impl_brace(*this);
 
+  if (decl->isUnion()) {
+    StrCat(std::format("fn byte_size() -> usize {{ {} }}",
+                       ctx_.getTypeSize(ctx_.getCanonicalTagType(decl)) / 8));
+    StrCat("fn to_bytes(&self, buf: &mut [u8]) { "
+           "buf.copy_from_slice(&self.__bytes.borrow()); }");
+    StrCat(std::format("fn from_bytes(buf: &[u8]) -> Self {{ {} {{ __bytes: "
+                       "Rc::new(RefCell::new(Box::from(buf))) }} }}",
+                       struct_name));
+    return;
+  }
+
   const auto &layout = ctx_.getASTRecordLayout(decl);
 
   StrCat(std::format("fn byte_size() -> usize {{ {} }}",

tests/unit/out/refcount/tag_vs_identifier_collision.rs

@@ -97,7 +97,19 @@ impl Default for point {
         }
     }
 }
-impl ByteRepr for point {}
+impl ByteRepr for point {
+    fn byte_size() -> usize {
+        4
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        buf.copy_from_slice(&self.__bytes.borrow());
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        point {
+            __bytes: Rc::new(RefCell::new(Box::from(buf))),
+        }
+    }
+}
 pub struct slot_union {
     __bytes: Value<Box<[u8]>>,
 }
@@ -123,7 +135,19 @@ impl Default for slot_union {
         }
     }
 }
-impl ByteRepr for slot_union {}
+impl ByteRepr for slot_union {
+    fn byte_size() -> usize {
+        4
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        buf.copy_from_slice(&self.__bytes.borrow());
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        slot_union {
+            __bytes: Rc::new(RefCell::new(Box::from(buf))),
+        }
+    }
+}
 #[derive(Clone, Copy, PartialEq, Debug, Default)]
 enum slot {
     #[default]

tests/unit/out/refcount/union_basic.rs

@@ -31,7 +31,19 @@ impl Default for basic {
         }
     }
 }
-impl ByteRepr for basic {}
+impl ByteRepr for basic {
+    fn byte_size() -> usize {
+        4
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        buf.copy_from_slice(&self.__bytes.borrow());
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        basic {
+            __bytes: Rc::new(RefCell::new(Box::from(buf))),
+        }
+    }
+}
 pub fn main() {
     std::process::exit(main_0());
 }

tests/unit/out/refcount/union_pointer_pun_writethrough.rs

@@ -36,7 +36,19 @@ fn main_0() -> i32 {
             }
         }
     }
-    impl ByteRepr for anon_0 {};
+    impl ByteRepr for anon_0 {
+        fn byte_size() -> usize {
+            8
+        }
+        fn to_bytes(&self, buf: &mut [u8]) {
+            buf.copy_from_slice(&self.__bytes.borrow());
+        }
+        fn from_bytes(buf: &[u8]) -> Self {
+            anon_0 {
+                __bytes: Rc::new(RefCell::new(Box::from(buf))),
+            }
+        }
+    };
     let pp: Value<anon_0> = <Value<anon_0>>::default();
     (*pp.borrow_mut()).as_signed().write((x.as_pointer()));
     ((*pp.borrow()).as_unsigned().read()).write(42_u64);

tests/unit/out/refcount/union_tagged_struct_arms.rs

@@ -122,14 +122,42 @@ impl Default for anon_0 {
         }
     }
 }
-impl ByteRepr for anon_0 {}
+impl ByteRepr for anon_0 {
+    fn byte_size() -> usize {
+        40
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        buf.copy_from_slice(&self.__bytes.borrow());
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        anon_0 {
+            __bytes: Rc::new(RefCell::new(Box::from(buf))),
+        }
+    }
+}
 #[derive(Default)]
 pub struct Branch {
     pub choice: Value<Choice_enum>,
     pub index: Value<i32>,
     pub v: Value<anon_0>,
 }
-impl ByteRepr for Branch {}
+impl ByteRepr for Branch {
+    fn byte_size() -> usize {
+        48
+    }
+    fn to_bytes(&self, buf: &mut [u8]) {
+        (*self.choice.borrow()).to_bytes(&mut buf[0..4]);
+        (*self.index.borrow()).to_bytes(&mut buf[4..8]);
+        (*self.v.borrow()).to_bytes(&mut buf[8..48]);
+    }
+    fn from_bytes(buf: &[u8]) -> Self {
+        Self {
+            choice: Rc::new(RefCell::new(<Choice_enum>::from_bytes(&buf[0..4]))),
+            index: Rc::new(RefCell::new(<i32>::from_bytes(&buf[4..8]))),
+            v: Rc::new(RefCell::new(<anon_0>::from_bytes(&buf[8..48]))),
+        }
+    }
+}
 pub fn main() {
     std::process::exit(main_0());
 }