don't emit #[repr(align(0))] for empty unions

src/ir/comp.rs

@@ -1078,8 +1078,14 @@ impl CompInfo {
             return None;
         }
 
+        // empty union case
+        if self.fields().is_empty() {
+            return None;
+        }
+
         let mut max_size = 0;
-        let mut max_align = 0;
+        // Don't allow align(0)
+        let mut max_align = 1;
         for field in self.fields() {
             let field_layout = field.layout(ctx);
 

tests/expectations/tests/empty-union.rs

@@ -0,0 +1,19 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub union a__bindgen_ty_1 {
+    pub _address: u8,
+}
+impl Default for a__bindgen_ty_1 {
+    fn default() -> Self {
+        unsafe { ::std::mem::zeroed() }
+    }
+}

tests/expectations/tests/issue-493_1_0.rs

@@ -1,6 +1,11 @@
 /* automatically generated by rust-bindgen */
 
-#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
 
 #[repr(C)]
 pub struct __BindgenUnionField<T>(::std::marker::PhantomData<T>);
@@ -91,17 +96,12 @@ impl Default for basic_string___short {
     }
 }
 #[repr(C)]
-#[derive(Copy, Clone)]
+#[derive(Debug, Default, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct basic_string___ulx {
     pub __lx: __BindgenUnionField<basic_string___long>,
     pub __lxx: __BindgenUnionField<basic_string___short>,
     pub bindgen_union_field: [u8; 0usize],
 }
-impl Default for basic_string___ulx {
-    fn default() -> Self {
-        unsafe { ::std::mem::zeroed() }
-    }
-}
 pub const basic_string___n_words: basic_string__bindgen_ty_2 =
     basic_string__bindgen_ty_2::__n_words;
 #[repr(i32)]
@@ -120,25 +120,15 @@ impl Default for basic_string___raw {
     }
 }
 #[repr(C)]
-#[derive(Copy, Clone)]
+#[derive(Debug, Default, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct basic_string___rep {
     pub __bindgen_anon_1: basic_string___rep__bindgen_ty_1,
 }
 #[repr(C)]
-#[derive(Copy, Clone)]
+#[derive(Debug, Default, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct basic_string___rep__bindgen_ty_1 {
     pub __l: __BindgenUnionField<basic_string___long>,
     pub __s: __BindgenUnionField<basic_string___short>,
     pub __r: __BindgenUnionField<basic_string___raw>,
     pub bindgen_union_field: [u8; 0usize],
 }
-impl Default for basic_string___rep__bindgen_ty_1 {
-    fn default() -> Self {
-        unsafe { ::std::mem::zeroed() }
-    }
-}
-impl Default for basic_string___rep {
-    fn default() -> Self {
-        unsafe { ::std::mem::zeroed() }
-    }
-}

tests/expectations/tests/transform-op.rs

@@ -63,7 +63,7 @@ impl<T> Default for StylePoint<T> {
     }
 }
 #[repr(C)]
-#[derive(Copy, Clone)]
+#[derive(Debug, Default, Copy, Clone)]
 pub struct StyleFoo<T> {
     pub __bindgen_anon_1: __BindgenUnionField<StyleFoo__bindgen_ty_1>,
     pub foo: __BindgenUnionField<StyleFoo_Foo_Body<T>>,
@@ -125,13 +125,8 @@ impl Default for StyleFoo__bindgen_ty_1 {
         unsafe { ::std::mem::zeroed() }
     }
 }
-impl<T> Default for StyleFoo<T> {
-    fn default() -> Self {
-        unsafe { ::std::mem::zeroed() }
-    }
-}
 #[repr(C)]
-#[derive(Copy, Clone)]
+#[derive(Debug, Copy, Clone)]
 pub struct StyleBar<T> {
     pub tag: StyleBar_Tag,
     pub __bindgen_anon_1: StyleBar__bindgen_ty_1<T>,
@@ -178,19 +173,14 @@ impl<T> Default for StyleBar_StyleBar3_Body<T> {
     }
 }
 #[repr(C)]
-#[derive(Copy, Clone)]
+#[derive(Debug, Default, Copy, Clone)]
 pub struct StyleBar__bindgen_ty_1<T> {
     pub bar1: __BindgenUnionField<StyleBar_StyleBar1_Body<T>>,
     pub bar2: __BindgenUnionField<StyleBar_StyleBar2_Body<T>>,
     pub bar3: __BindgenUnionField<StyleBar_StyleBar3_Body<T>>,
     pub bindgen_union_field: [u8; 0usize],
     pub _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
-impl<T> Default for StyleBar__bindgen_ty_1<T> {
-    fn default() -> Self {
-        unsafe { ::std::mem::zeroed() }
-    }
-}
 impl<T> Default for StyleBar<T> {
     fn default() -> Self {
         unsafe { ::std::mem::zeroed() }

tests/headers/empty-union.hpp

@@ -0,0 +1,5 @@
+// bindgen-flags: --opaque-type "*"
+
+template <int> class a {
+  union {};
+};