codegen: Don't assume unsized structs have address.

Per C semantics, they may not.

Author: emilio

src/codegen/mod.rs

@@ -1286,17 +1286,25 @@ impl CodeGenerator for CompInfo {
             }
         }
 
-        // C requires every struct to be addressable, so what C compilers do is
-        // making the struct 1-byte sized.
+        // C++ requires every struct to be addressable, so what C++ compilers do
+        // is making the struct 1-byte sized.
+        //
+        // This is apparently not the case for C, see:
+        // https://github.com/servo/rust-bindgen/issues/551
+        //
+        // Just get the layout, and assume C++ if not.
         //
         // NOTE: This check is conveniently here to avoid the dummy fields we
         // may add for unused template parameters.
         if self.is_unsized(ctx) {
-            let ty = BlobTyBuilder::new(Layout::new(1, 1)).build();
-            let field = StructFieldBuilder::named("_address")
-                .pub_()
-                .build_ty(ty);
-            fields.push(field);
+            let has_address = layout.map_or(true, |l| l.size != 0);
+            if has_address {
+                let ty = BlobTyBuilder::new(Layout::new(1, 1)).build();
+                let field = StructFieldBuilder::named("_address")
+                    .pub_()
+                    .build_ty(ty);
+                fields.push(field);
+            }
         }
 
         // Append any extra template arguments that nobody has used so far.

tests/expectations/tests/c-empty-layout.rs

@@ -0,0 +1,20 @@
+/* automatically generated by rust-bindgen */
+
+
+#![allow(non_snake_case)]
+
+
+#[repr(C)]
+#[derive(Debug, Default, Copy)]
+pub struct Foo {
+}
+#[test]
+fn bindgen_test_layout_Foo() {
+    assert_eq!(::std::mem::size_of::<Foo>() , 0usize , concat ! (
+               "Size of: " , stringify ! ( Foo ) ));
+    assert_eq! (::std::mem::align_of::<Foo>() , 1usize , concat ! (
+                "Alignment of " , stringify ! ( Foo ) ));
+}
+impl Clone for Foo {
+    fn clone(&self) -> Self { *self }
+}

tests/expectations/tests/cpp-empty-layout.rs

@@ -0,0 +1,21 @@
+/* automatically generated by rust-bindgen */
+
+
+#![allow(non_snake_case)]
+
+
+#[repr(C)]
+#[derive(Debug, Default, Copy)]
+pub struct Foo {
+    pub _address: u8,
+}
+#[test]
+fn bindgen_test_layout_Foo() {
+    assert_eq!(::std::mem::size_of::<Foo>() , 1usize , concat ! (
+               "Size of: " , stringify ! ( Foo ) ));
+    assert_eq! (::std::mem::align_of::<Foo>() , 1usize , concat ! (
+                "Alignment of " , stringify ! ( Foo ) ));
+}
+impl Clone for Foo {
+    fn clone(&self) -> Self { *self }
+}

tests/headers/c-empty-layout.h

@@ -0,0 +1 @@
+struct Foo {};

tests/headers/cpp-empty-layout.hpp

@@ -0,0 +1 @@
+struct Foo {};