From 43c43ba80f84704c5dc976e1669edf8e898286b3 Mon Sep 17 00:00:00 2001
From: Nick Fitzgerald <fitzgen@gmail.com>
Date: Fri, 8 Dec 2017 15:42:59 -0800
Subject: [PATCH] Always add `repr(C)` to rustified enums

If we don't, then eddyb's recent layout optimizations will do unexpected things
to them.

We also need to handle empty `enum`s without variants. When `repr(C)` is on a
Rust `enum`, it cannot be empty, so we need to add a dummy.
---
 src/codegen/mod.rs                            | 43 +++++++++++--------
 tests/expectations/tests/anon_enum.rs         |  2 +
 tests/expectations/tests/anon_enum_trait.rs   |  2 +
 .../expectations/tests/anon_enum_whitelist.rs |  1 +
 tests/expectations/tests/anon_union.rs        |  1 +
 tests/expectations/tests/anon_union_1_0.rs    |  1 +
 tests/expectations/tests/bitfield_align_2.rs  |  1 +
 .../tests/class_with_inner_struct.rs          |  1 +
 .../tests/class_with_inner_struct_1_0.rs      |  1 +
 .../expectations/tests/const_enum_unnamed.rs  |  2 +
 tests/expectations/tests/constify-enum.rs     |  1 +
 tests/expectations/tests/empty-enum.rs        | 36 ++++++++++++++++
 tests/expectations/tests/enum.rs              |  2 +
 tests/expectations/tests/enum_alias.rs        |  1 +
 .../tests/enum_and_vtable_mangling.rs         |  1 +
 tests/expectations/tests/enum_dupe.rs         |  1 +
 .../expectations/tests/enum_explicit_type.rs  |  6 +++
 .../tests/enum_in_template_with_typedef.rs    |  1 +
 tests/expectations/tests/enum_negative.rs     |  1 +
 tests/expectations/tests/enum_packed.rs       |  3 ++
 tests/expectations/tests/forward-enum-decl.rs |  1 +
 .../expectations/tests/func_ptr_in_struct.rs  |  6 ++-
 tests/expectations/tests/issue-372.rs         |  1 +
 tests/expectations/tests/issue-410.rs         |  6 ++-
 tests/expectations/tests/issue-493.rs         |  2 +
 tests/expectations/tests/issue-493_1_0.rs     |  2 +
 ...ate-params-causing-layout-test-failures.rs |  1 +
 .../tests/issue-888-enum-var-decl-jump.rs     |  6 ++-
 .../expectations/tests/jsval_layout_opaque.rs |  4 ++
 .../tests/jsval_layout_opaque_1_0.rs          |  4 ++
 .../tests/layout_array_too_long.rs            |  1 +
 .../tests/layout_cmdline_token.rs             |  4 +-
 tests/expectations/tests/layout_eth_conf.rs   |  8 ++++
 .../expectations/tests/layout_eth_conf_1_0.rs |  8 ++++
 .../tests/layout_large_align_field.rs         |  1 +
 .../tests/libclang-3.8/constant-evaluate.rs   |  1 +
 .../tests/libclang-3.9/constant-evaluate.rs   |  1 +
 .../tests/libclang-4/constant-evaluate.rs     |  1 +
 tests/expectations/tests/nsStyleAutoArray.rs  |  1 +
 tests/expectations/tests/overflowed_enum.rs   |  2 +
 .../tests/prepend-enum-constified-variant.rs  |  1 +
 tests/expectations/tests/short-enums.rs       |  3 ++
 tests/expectations/tests/struct_typedef.rs    |  2 +
 tests/expectations/tests/struct_typedef_ns.rs |  2 +
 tests/expectations/tests/weird_bitfields.rs   |  1 +
 tests/headers/empty-enum.h                    | 15 +++++++
 46 files changed, 171 insertions(+), 22 deletions(-)
 create mode 100644 tests/expectations/tests/empty-enum.rs
 create mode 100644 tests/headers/empty-enum.h

diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index db8fc4ddba..b8893f9c41 100644
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -2148,7 +2148,10 @@ impl EnumVariation {
 
 /// A helper type to construct different enum variations.
 enum EnumBuilder<'a> {
-    Rust(quote::Tokens),
+    Rust {
+        tokens: quote::Tokens,
+        emitted_any_variants: bool,
+    },
     Bitfield {
         canonical_name: &'a str,
         tokens: quote::Tokens,
@@ -2188,7 +2191,10 @@ impl<'a> EnumBuilder<'a> {
                     pub enum #ident
                 };
                 tokens.append("{");
-                EnumBuilder::Rust(tokens)
+                EnumBuilder::Rust {
+                    tokens,
+                    emitted_any_variants: false,
+                }
             }
 
             EnumVariation::Consts => {
@@ -2229,12 +2235,15 @@ impl<'a> EnumBuilder<'a> {
         };
 
         match self {
-            EnumBuilder::Rust(tokens) => {
+            EnumBuilder::Rust { tokens, emitted_any_variants: _ } => {
                 let name = ctx.rust_ident(variant_name);
-                EnumBuilder::Rust(quote! {
-                    #tokens
-                    #name = #expr,
-                })
+                EnumBuilder::Rust {
+                    tokens: quote! {
+                        #tokens
+                        #name = #expr,
+                    },
+                    emitted_any_variants: true,
+                }
             }
 
             EnumBuilder::Bitfield { .. } => {
@@ -2295,9 +2304,12 @@ impl<'a> EnumBuilder<'a> {
         result: &mut CodegenResult<'b>,
     ) -> quote::Tokens {
         match self {
-            EnumBuilder::Rust(mut t) => {
-                t.append("}");
-                t
+            EnumBuilder::Rust { mut tokens, emitted_any_variants } => {
+                if !emitted_any_variants {
+                    tokens.append(quote! { __bindgen_cannot_repr_c_on_empty_enum = 0 });
+                }
+                tokens.append("}");
+                tokens
             }
             EnumBuilder::Bitfield {
                 canonical_name,
@@ -2432,15 +2444,12 @@ impl CodeGenerator for Enum {
 
         let mut attrs = vec![];
 
-        // FIXME: Rust forbids repr with empty enums. Remove this condition when
-        // this is allowed.
-        //
         // TODO(emilio): Delegate this to the builders?
         if variation.is_rust() {
-            if !self.variants().is_empty() {
-                attrs.push(attributes::repr(repr_name));
-            }
-        } else if variation.is_bitfield() {
+            attrs.push(attributes::repr(repr_name));
+        }
+
+        if variation.is_bitfield() || variation.is_rust() {
             attrs.push(attributes::repr("C"));
         }
 
diff --git a/tests/expectations/tests/anon_enum.rs b/tests/expectations/tests/anon_enum.rs
index 718905d9bb..c482530c87 100644
--- a/tests/expectations/tests/anon_enum.rs
+++ b/tests/expectations/tests/anon_enum.rs
@@ -12,6 +12,7 @@ pub struct Test {
 }
 pub const Test_T_NONE: Test__bindgen_ty_1 = Test__bindgen_ty_1::T_NONE;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Test__bindgen_ty_1 {
     T_NONE = 0,
@@ -40,6 +41,7 @@ fn bindgen_test_layout_Test() {
     );
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Baz {
     Foo = 0,
diff --git a/tests/expectations/tests/anon_enum_trait.rs b/tests/expectations/tests/anon_enum_trait.rs
index 9f5a6c56f1..21d2287944 100644
--- a/tests/expectations/tests/anon_enum_trait.rs
+++ b/tests/expectations/tests/anon_enum_trait.rs
@@ -19,6 +19,7 @@ pub const DataType_channels: DataType__bindgen_ty_1 = DataType__bindgen_ty_1::ge
 pub const DataType_fmt: DataType__bindgen_ty_1 = DataType__bindgen_ty_1::generic_type;
 pub const DataType_type_: DataType__bindgen_ty_1 = DataType__bindgen_ty_1::generic_type;
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum DataType__bindgen_ty_1 {
     generic_type = 0,
@@ -31,6 +32,7 @@ pub struct Foo {
 pub const Foo_Bar: Foo__bindgen_ty_1 = Foo__bindgen_ty_1::Bar;
 pub const Foo_Baz: Foo__bindgen_ty_1 = Foo__bindgen_ty_1::Bar;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo__bindgen_ty_1 {
     Bar = 0,
diff --git a/tests/expectations/tests/anon_enum_whitelist.rs b/tests/expectations/tests/anon_enum_whitelist.rs
index c639410f9a..45b858fdea 100644
--- a/tests/expectations/tests/anon_enum_whitelist.rs
+++ b/tests/expectations/tests/anon_enum_whitelist.rs
@@ -7,6 +7,7 @@
 pub const NODE_FLAG_FOO: _bindgen_ty_1 = _bindgen_ty_1::NODE_FLAG_FOO;
 pub const NODE_FLAG_BAR: _bindgen_ty_1 = _bindgen_ty_1::NODE_FLAG_BAR;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     NODE_FLAG_FOO = 0,
diff --git a/tests/expectations/tests/anon_union.rs b/tests/expectations/tests/anon_union.rs
index fdf01a7a5d..da990ae9aa 100644
--- a/tests/expectations/tests/anon_union.rs
+++ b/tests/expectations/tests/anon_union.rs
@@ -14,6 +14,7 @@ pub struct TErrorResult {
 pub const TErrorResult_UnionState_HasException: TErrorResult_UnionState =
     TErrorResult_UnionState::HasMessage;
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum TErrorResult_UnionState {
     HasMessage = 0,
diff --git a/tests/expectations/tests/anon_union_1_0.rs b/tests/expectations/tests/anon_union_1_0.rs
index 8d19c9fc3d..67a332c01c 100644
--- a/tests/expectations/tests/anon_union_1_0.rs
+++ b/tests/expectations/tests/anon_union_1_0.rs
@@ -58,6 +58,7 @@ pub struct TErrorResult {
 pub const TErrorResult_UnionState_HasException: TErrorResult_UnionState =
     TErrorResult_UnionState::HasMessage;
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum TErrorResult_UnionState {
     HasMessage = 0,
diff --git a/tests/expectations/tests/bitfield_align_2.rs b/tests/expectations/tests/bitfield_align_2.rs
index 6f4a0f693e..5174d1aabc 100644
--- a/tests/expectations/tests/bitfield_align_2.rs
+++ b/tests/expectations/tests/bitfield_align_2.rs
@@ -84,6 +84,7 @@ where
     }
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum MyEnum {
     ONE = 0,
diff --git a/tests/expectations/tests/class_with_inner_struct.rs b/tests/expectations/tests/class_with_inner_struct.rs
index ecdbdf9fd6..f656012584 100644
--- a/tests/expectations/tests/class_with_inner_struct.rs
+++ b/tests/expectations/tests/class_with_inner_struct.rs
@@ -214,6 +214,7 @@ fn bindgen_test_layout_B() {
     );
 }
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum StepSyntax {
     Keyword = 0,
diff --git a/tests/expectations/tests/class_with_inner_struct_1_0.rs b/tests/expectations/tests/class_with_inner_struct_1_0.rs
index 1236950ccd..e807236232 100644
--- a/tests/expectations/tests/class_with_inner_struct_1_0.rs
+++ b/tests/expectations/tests/class_with_inner_struct_1_0.rs
@@ -272,6 +272,7 @@ impl Clone for B {
     }
 }
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum StepSyntax {
     Keyword = 0,
diff --git a/tests/expectations/tests/const_enum_unnamed.rs b/tests/expectations/tests/const_enum_unnamed.rs
index 539c8916c6..833f835172 100644
--- a/tests/expectations/tests/const_enum_unnamed.rs
+++ b/tests/expectations/tests/const_enum_unnamed.rs
@@ -7,6 +7,7 @@
 pub const FOO_BAR: _bindgen_ty_1 = _bindgen_ty_1::FOO_BAR;
 pub const FOO_BAZ: _bindgen_ty_1 = _bindgen_ty_1::FOO_BAZ;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     FOO_BAR = 0,
@@ -19,6 +20,7 @@ pub struct Foo {
 }
 pub const Foo_FOO_BAR: Foo__bindgen_ty_1 = Foo__bindgen_ty_1::FOO_BAR;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo__bindgen_ty_1 {
     FOO_BAR = 10,
diff --git a/tests/expectations/tests/constify-enum.rs b/tests/expectations/tests/constify-enum.rs
index 78644ae4d5..79fc4dff31 100644
--- a/tests/expectations/tests/constify-enum.rs
+++ b/tests/expectations/tests/constify-enum.rs
@@ -9,6 +9,7 @@ pub const nsCSSPropertyID_eCSSProperty_COUNT_unexistingVariantValue: nsCSSProper
 pub const nsCSSPropertyID_eCSSProperty_COUNT: nsCSSPropertyID =
     nsCSSPropertyID::eCSSPropertyAlias_aa;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum nsCSSPropertyID {
     eCSSProperty_a = 0,
diff --git a/tests/expectations/tests/empty-enum.rs b/tests/expectations/tests/empty-enum.rs
new file mode 100644
index 0000000000..4ec7df8a63
--- /dev/null
+++ b/tests/expectations/tests/empty-enum.rs
@@ -0,0 +1,36 @@
+/* automatically generated by rust-bindgen */
+
+
+#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]
+
+
+pub type EmptyConstified = ::std::os::raw::c_uint;
+#[repr(u32)]
+#[repr(C)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum EmptyRustified {
+    __bindgen_cannot_repr_c_on_empty_enum = 0,
+}
+pub mod EmptyModule {
+    pub type Type = ::std::os::raw::c_uint;
+}
+#[repr(i8)]
+#[repr(C)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum EmptyClassRustified {
+    __bindgen_cannot_repr_c_on_empty_enum = 0,
+}
+pub type EmptyClassConstified = ::std::os::raw::c_char;
+pub mod EmptyClassModule {
+    pub type Type = ::std::os::raw::c_char;
+}
+#[repr(i8)]
+#[repr(C)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum ForwardClassRustified {
+    __bindgen_cannot_repr_c_on_empty_enum = 0,
+}
+pub type ForwardClassConstified = ::std::os::raw::c_char;
+pub mod ForwardClassModule {
+    pub type Type = ::std::os::raw::c_char;
+}
diff --git a/tests/expectations/tests/enum.rs b/tests/expectations/tests/enum.rs
index 70c308307f..b1920aaef0 100644
--- a/tests/expectations/tests/enum.rs
+++ b/tests/expectations/tests/enum.rs
@@ -5,12 +5,14 @@
 
 
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo {
     Bar = 0,
     Qux = 1,
 }
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Neg {
     MinusOne = -1,
diff --git a/tests/expectations/tests/enum_alias.rs b/tests/expectations/tests/enum_alias.rs
index f12c08d347..cde429f762 100644
--- a/tests/expectations/tests/enum_alias.rs
+++ b/tests/expectations/tests/enum_alias.rs
@@ -5,6 +5,7 @@
 
 
 #[repr(u8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Bar {
     VAL = 0,
diff --git a/tests/expectations/tests/enum_and_vtable_mangling.rs b/tests/expectations/tests/enum_and_vtable_mangling.rs
index e9e6f13cc6..42ee383214 100644
--- a/tests/expectations/tests/enum_and_vtable_mangling.rs
+++ b/tests/expectations/tests/enum_and_vtable_mangling.rs
@@ -7,6 +7,7 @@
 pub const match_: _bindgen_ty_1 = _bindgen_ty_1::match_;
 pub const whatever_else: _bindgen_ty_1 = _bindgen_ty_1::whatever_else;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     match_ = 0,
diff --git a/tests/expectations/tests/enum_dupe.rs b/tests/expectations/tests/enum_dupe.rs
index a91999ed2b..151b2cd027 100644
--- a/tests/expectations/tests/enum_dupe.rs
+++ b/tests/expectations/tests/enum_dupe.rs
@@ -6,6 +6,7 @@
 
 pub const Foo_Dupe: Foo = Foo::Bar;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo {
     Bar = 1,
diff --git a/tests/expectations/tests/enum_explicit_type.rs b/tests/expectations/tests/enum_explicit_type.rs
index 7ff0ef51e4..644a1cea41 100644
--- a/tests/expectations/tests/enum_explicit_type.rs
+++ b/tests/expectations/tests/enum_explicit_type.rs
@@ -5,34 +5,40 @@
 
 
 #[repr(u8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo {
     Bar = 0,
     Qux = 1,
 }
 #[repr(i8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Neg {
     MinusOne = -1,
     One = 1,
 }
 #[repr(u16)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Bigger {
     Much = 255,
     Larger = 256,
 }
 #[repr(i64)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum MuchLong {
     MuchLow = -4294967296,
 }
 #[repr(i64)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum MuchLongLong {
     I64_MIN = -9223372036854775808,
 }
 #[repr(u64)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum MuchULongLong {
     MuchHigh = 4294967296,
diff --git a/tests/expectations/tests/enum_in_template_with_typedef.rs b/tests/expectations/tests/enum_in_template_with_typedef.rs
index 06dea12630..588bb42b9e 100644
--- a/tests/expectations/tests/enum_in_template_with_typedef.rs
+++ b/tests/expectations/tests/enum_in_template_with_typedef.rs
@@ -13,6 +13,7 @@ pub type std_fbstring_core_category_type = u8;
 pub const std_fbstring_core_Category_Bar: std_fbstring_core_Category =
     std_fbstring_core_Category::Foo;
 #[repr(u8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum std_fbstring_core_Category {
     Foo = 0,
diff --git a/tests/expectations/tests/enum_negative.rs b/tests/expectations/tests/enum_negative.rs
index 100f27db2e..1fe2f6a4ba 100644
--- a/tests/expectations/tests/enum_negative.rs
+++ b/tests/expectations/tests/enum_negative.rs
@@ -5,6 +5,7 @@
 
 
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo {
     Bar = -2,
diff --git a/tests/expectations/tests/enum_packed.rs b/tests/expectations/tests/enum_packed.rs
index cc85b55326..d8e96b0ffb 100644
--- a/tests/expectations/tests/enum_packed.rs
+++ b/tests/expectations/tests/enum_packed.rs
@@ -5,18 +5,21 @@
 
 
 #[repr(u8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo {
     Bar = 0,
     Qux = 1,
 }
 #[repr(i8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Neg {
     MinusOne = -1,
     One = 1,
 }
 #[repr(u16)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Bigger {
     Much = 255,
diff --git a/tests/expectations/tests/forward-enum-decl.rs b/tests/expectations/tests/forward-enum-decl.rs
index 5502c4c4f8..c2dea97aeb 100644
--- a/tests/expectations/tests/forward-enum-decl.rs
+++ b/tests/expectations/tests/forward-enum-decl.rs
@@ -5,6 +5,7 @@
 
 
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum CSSPseudoClassType {
     empty = 0,
diff --git a/tests/expectations/tests/func_ptr_in_struct.rs b/tests/expectations/tests/func_ptr_in_struct.rs
index 290a148c0e..33d908e20e 100644
--- a/tests/expectations/tests/func_ptr_in_struct.rs
+++ b/tests/expectations/tests/func_ptr_in_struct.rs
@@ -4,8 +4,12 @@
 #![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]
 
 
+#[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-pub enum baz {}
+pub enum baz {
+    __bindgen_cannot_repr_c_on_empty_enum = 0,
+}
 #[repr(C)]
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct Foo {
diff --git a/tests/expectations/tests/issue-372.rs b/tests/expectations/tests/issue-372.rs
index b2949da362..f9040a9982 100644
--- a/tests/expectations/tests/issue-372.rs
+++ b/tests/expectations/tests/issue-372.rs
@@ -77,6 +77,7 @@ pub mod root {
         }
     }
     #[repr(u32)]
+    #[repr(C)]
     #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
     pub enum n {
         o = 0,
diff --git a/tests/expectations/tests/issue-410.rs b/tests/expectations/tests/issue-410.rs
index 928701ef18..f23462bf6c 100644
--- a/tests/expectations/tests/issue-410.rs
+++ b/tests/expectations/tests/issue-410.rs
@@ -40,6 +40,10 @@ pub mod root {
             }
         }
     }
+    #[repr(u32)]
+    #[repr(C)]
     #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-    pub enum JSWhyMagic {}
+    pub enum JSWhyMagic {
+        __bindgen_cannot_repr_c_on_empty_enum = 0,
+    }
 }
diff --git a/tests/expectations/tests/issue-493.rs b/tests/expectations/tests/issue-493.rs
index 8975938d40..d338e30cf3 100644
--- a/tests/expectations/tests/issue-493.rs
+++ b/tests/expectations/tests/issue-493.rs
@@ -70,6 +70,7 @@ impl Default for basic_string___long {
 pub const basic_string___min_cap: basic_string__bindgen_ty_1 =
     basic_string__bindgen_ty_1::__min_cap;
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum basic_string__bindgen_ty_1 {
     __min_cap = 0,
@@ -109,6 +110,7 @@ impl Default for basic_string___ulx {
 pub const basic_string___n_words: basic_string__bindgen_ty_2 =
     basic_string__bindgen_ty_2::__n_words;
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum basic_string__bindgen_ty_2 {
     __n_words = 0,
diff --git a/tests/expectations/tests/issue-493_1_0.rs b/tests/expectations/tests/issue-493_1_0.rs
index da6dac7700..4dfc26d8d6 100644
--- a/tests/expectations/tests/issue-493_1_0.rs
+++ b/tests/expectations/tests/issue-493_1_0.rs
@@ -70,6 +70,7 @@ impl Default for basic_string___long {
 pub const basic_string___min_cap: basic_string__bindgen_ty_1 =
     basic_string__bindgen_ty_1::__min_cap;
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum basic_string__bindgen_ty_1 {
     __min_cap = 0,
@@ -107,6 +108,7 @@ impl Default for basic_string___ulx {
 pub const basic_string___n_words: basic_string__bindgen_ty_2 =
     basic_string__bindgen_ty_2::__n_words;
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum basic_string__bindgen_ty_2 {
     __n_words = 0,
diff --git a/tests/expectations/tests/issue-569-non-type-template-params-causing-layout-test-failures.rs b/tests/expectations/tests/issue-569-non-type-template-params-causing-layout-test-failures.rs
index b2ddf7138c..3029a67032 100644
--- a/tests/expectations/tests/issue-569-non-type-template-params-causing-layout-test-failures.rs
+++ b/tests/expectations/tests/issue-569-non-type-template-params-causing-layout-test-failures.rs
@@ -7,6 +7,7 @@
 pub const ENUM_VARIANT_1: _bindgen_ty_1 = _bindgen_ty_1::ENUM_VARIANT_1;
 pub const ENUM_VARIANT_2: _bindgen_ty_1 = _bindgen_ty_1::ENUM_VARIANT_2;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     ENUM_VARIANT_1 = 0,
diff --git a/tests/expectations/tests/issue-888-enum-var-decl-jump.rs b/tests/expectations/tests/issue-888-enum-var-decl-jump.rs
index 61cbfc3a48..c0ac112d18 100644
--- a/tests/expectations/tests/issue-888-enum-var-decl-jump.rs
+++ b/tests/expectations/tests/issue-888-enum-var-decl-jump.rs
@@ -34,6 +34,10 @@ pub mod root {
             );
         }
     }
+    #[repr(u32)]
+    #[repr(C)]
     #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-    pub enum a {}
+    pub enum a {
+        __bindgen_cannot_repr_c_on_empty_enum = 0,
+    }
 }
diff --git a/tests/expectations/tests/jsval_layout_opaque.rs b/tests/expectations/tests/jsval_layout_opaque.rs
index 80526b3e79..2b2d0d77f9 100644
--- a/tests/expectations/tests/jsval_layout_opaque.rs
+++ b/tests/expectations/tests/jsval_layout_opaque.rs
@@ -87,6 +87,7 @@ pub const JSVAL_TAG_SHIFT: ::std::os::raw::c_uint = 47;
 pub const JSVAL_PAYLOAD_MASK: ::std::os::raw::c_ulonglong = 140737488355327;
 pub const JSVAL_TAG_MASK: ::std::os::raw::c_longlong = -140737488355328;
 #[repr(u8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSValueType {
     JSVAL_TYPE_DOUBLE = 0,
@@ -102,6 +103,7 @@ pub enum JSValueType {
     JSVAL_TYPE_MISSING = 33,
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSValueTag {
     JSVAL_TAG_MAX_DOUBLE = 131056,
@@ -115,6 +117,7 @@ pub enum JSValueTag {
     JSVAL_TAG_OBJECT = 131064,
 }
 #[repr(u64)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSValueShiftedTag {
     JSVAL_SHIFTED_TAG_MAX_DOUBLE = 18444492278190833663,
@@ -128,6 +131,7 @@ pub enum JSValueShiftedTag {
     JSVAL_SHIFTED_TAG_OBJECT = 18445618173802708992,
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSWhyMagic {
     JS_ELEMENTS_HOLE = 0,
diff --git a/tests/expectations/tests/jsval_layout_opaque_1_0.rs b/tests/expectations/tests/jsval_layout_opaque_1_0.rs
index cac9b0b8e2..ab11a23165 100644
--- a/tests/expectations/tests/jsval_layout_opaque_1_0.rs
+++ b/tests/expectations/tests/jsval_layout_opaque_1_0.rs
@@ -130,6 +130,7 @@ pub const JSVAL_TAG_SHIFT: ::std::os::raw::c_uint = 47;
 pub const JSVAL_PAYLOAD_MASK: ::std::os::raw::c_ulonglong = 140737488355327;
 pub const JSVAL_TAG_MASK: ::std::os::raw::c_longlong = -140737488355328;
 #[repr(u8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSValueType {
     JSVAL_TYPE_DOUBLE = 0,
@@ -145,6 +146,7 @@ pub enum JSValueType {
     JSVAL_TYPE_MISSING = 33,
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSValueTag {
     JSVAL_TAG_MAX_DOUBLE = 131056,
@@ -158,6 +160,7 @@ pub enum JSValueTag {
     JSVAL_TAG_OBJECT = 131064,
 }
 #[repr(u64)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSValueShiftedTag {
     JSVAL_SHIFTED_TAG_MAX_DOUBLE = 18444492278190833663,
@@ -171,6 +174,7 @@ pub enum JSValueShiftedTag {
     JSVAL_SHIFTED_TAG_OBJECT = 18445618173802708992,
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum JSWhyMagic {
     JS_ELEMENTS_HOLE = 0,
diff --git a/tests/expectations/tests/layout_array_too_long.rs b/tests/expectations/tests/layout_array_too_long.rs
index b767757376..59884451b8 100644
--- a/tests/expectations/tests/layout_array_too_long.rs
+++ b/tests/expectations/tests/layout_array_too_long.rs
@@ -11,6 +11,7 @@ pub const IP_FIRST_FRAG_IDX: _bindgen_ty_1 = _bindgen_ty_1::IP_FIRST_FRAG_IDX;
 pub const IP_MIN_FRAG_NUM: _bindgen_ty_1 = _bindgen_ty_1::IP_MIN_FRAG_NUM;
 pub const IP_MAX_FRAG_NUM: _bindgen_ty_1 = _bindgen_ty_1::IP_MAX_FRAG_NUM;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     IP_LAST_FRAG_IDX = 0,
diff --git a/tests/expectations/tests/layout_cmdline_token.rs b/tests/expectations/tests/layout_cmdline_token.rs
index 9115741670..2cde7c42cf 100644
--- a/tests/expectations/tests/layout_cmdline_token.rs
+++ b/tests/expectations/tests/layout_cmdline_token.rs
@@ -83,8 +83,7 @@ pub struct cmdline_token_ops {
     >,
     /// return the num of possible choices for this token
     pub complete_get_nb: ::std::option::Option<
-        unsafe extern "C" fn(arg1: *mut cmdline_parse_token_hdr_t)
-            -> ::std::os::raw::c_int,
+        unsafe extern "C" fn(arg1: *mut cmdline_parse_token_hdr_t) -> ::std::os::raw::c_int,
     >,
     /// return the elt x for this token (token, idx, dstbuf, size)
     pub complete_get_elt: ::std::option::Option<
@@ -167,6 +166,7 @@ impl Default for cmdline_token_ops {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum cmdline_numtype {
     UINT8 = 0,
diff --git a/tests/expectations/tests/layout_eth_conf.rs b/tests/expectations/tests/layout_eth_conf.rs
index 9721fb7b32..599f9788fe 100644
--- a/tests/expectations/tests/layout_eth_conf.rs
+++ b/tests/expectations/tests/layout_eth_conf.rs
@@ -116,6 +116,7 @@ pub const RTE_ETH_FLOW_GENEVE: ::std::os::raw::c_uint = 20;
 pub const RTE_ETH_FLOW_NVGRE: ::std::os::raw::c_uint = 21;
 pub const RTE_ETH_FLOW_MAX: ::std::os::raw::c_uint = 22;
 #[repr(u32)]
+#[repr(C)]
 /// A set of values to identify what method is to be used to route
 /// packets to multiple queues.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -343,6 +344,7 @@ impl rte_eth_rxmode {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 /// A set of values to identify what method is to be used to transmit
 /// packets using multi-TCs.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -532,6 +534,7 @@ impl Default for rte_eth_rss_conf {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 /// This enum indicates the possible number of traffic classes
 /// in DCB configratioins
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -540,6 +543,7 @@ pub enum rte_eth_nb_tcs {
     ETH_8_TCS = 8,
 }
 #[repr(u32)]
+#[repr(C)]
 /// This enum indicates the possible number of queue pools
 /// in VMDQ configurations.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -1054,6 +1058,7 @@ impl Default for rte_eth_vmdq_rx_conf {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 /// Flow Director setting modes: none, signature or perfect.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum rte_fdir_mode {
@@ -1064,6 +1069,7 @@ pub enum rte_fdir_mode {
     RTE_FDIR_MODE_PERFECT_TUNNEL = 4,
 }
 #[repr(u32)]
+#[repr(C)]
 /// Memory space that can be configured to store Flow Director filters
 /// in the board memory.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -1073,6 +1079,7 @@ pub enum rte_fdir_pballoc_type {
     RTE_FDIR_PBALLOC_256K = 2,
 }
 #[repr(u32)]
+#[repr(C)]
 /// Select report mode of FDIR hash information in RX descriptors.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum rte_fdir_status_mode {
@@ -1366,6 +1373,7 @@ fn bindgen_test_layout_rte_eth_fdir_masks() {
     );
 }
 #[repr(u32)]
+#[repr(C)]
 /// Payload type
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum rte_eth_payload_type {
diff --git a/tests/expectations/tests/layout_eth_conf_1_0.rs b/tests/expectations/tests/layout_eth_conf_1_0.rs
index ad37574d9c..532fcae8e1 100644
--- a/tests/expectations/tests/layout_eth_conf_1_0.rs
+++ b/tests/expectations/tests/layout_eth_conf_1_0.rs
@@ -159,6 +159,7 @@ pub const RTE_ETH_FLOW_GENEVE: ::std::os::raw::c_uint = 20;
 pub const RTE_ETH_FLOW_NVGRE: ::std::os::raw::c_uint = 21;
 pub const RTE_ETH_FLOW_MAX: ::std::os::raw::c_uint = 22;
 #[repr(u32)]
+#[repr(C)]
 /// A set of values to identify what method is to be used to route
 /// packets to multiple queues.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -391,6 +392,7 @@ impl rte_eth_rxmode {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 /// A set of values to identify what method is to be used to transmit
 /// packets using multi-TCs.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -590,6 +592,7 @@ impl Default for rte_eth_rss_conf {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 /// This enum indicates the possible number of traffic classes
 /// in DCB configratioins
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -598,6 +601,7 @@ pub enum rte_eth_nb_tcs {
     ETH_8_TCS = 8,
 }
 #[repr(u32)]
+#[repr(C)]
 /// This enum indicates the possible number of queue pools
 /// in VMDQ configurations.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -1152,6 +1156,7 @@ impl Default for rte_eth_vmdq_rx_conf {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 /// Flow Director setting modes: none, signature or perfect.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum rte_fdir_mode {
@@ -1162,6 +1167,7 @@ pub enum rte_fdir_mode {
     RTE_FDIR_MODE_PERFECT_TUNNEL = 4,
 }
 #[repr(u32)]
+#[repr(C)]
 /// Memory space that can be configured to store Flow Director filters
 /// in the board memory.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -1171,6 +1177,7 @@ pub enum rte_fdir_pballoc_type {
     RTE_FDIR_PBALLOC_256K = 2,
 }
 #[repr(u32)]
+#[repr(C)]
 /// Select report mode of FDIR hash information in RX descriptors.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum rte_fdir_status_mode {
@@ -1479,6 +1486,7 @@ impl Clone for rte_eth_fdir_masks {
     }
 }
 #[repr(u32)]
+#[repr(C)]
 /// Payload type
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum rte_eth_payload_type {
diff --git a/tests/expectations/tests/layout_large_align_field.rs b/tests/expectations/tests/layout_large_align_field.rs
index 21f8454677..501e1bcec7 100644
--- a/tests/expectations/tests/layout_large_align_field.rs
+++ b/tests/expectations/tests/layout_large_align_field.rs
@@ -48,6 +48,7 @@ pub const IP_FIRST_FRAG_IDX: _bindgen_ty_1 = _bindgen_ty_1::IP_FIRST_FRAG_IDX;
 pub const IP_MIN_FRAG_NUM: _bindgen_ty_1 = _bindgen_ty_1::IP_MIN_FRAG_NUM;
 pub const IP_MAX_FRAG_NUM: _bindgen_ty_1 = _bindgen_ty_1::IP_MAX_FRAG_NUM;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     IP_LAST_FRAG_IDX = 0,
diff --git a/tests/expectations/tests/libclang-3.8/constant-evaluate.rs b/tests/expectations/tests/libclang-3.8/constant-evaluate.rs
index 8faddfe969..1b6aca15b5 100644
--- a/tests/expectations/tests/libclang-3.8/constant-evaluate.rs
+++ b/tests/expectations/tests/libclang-3.8/constant-evaluate.rs
@@ -7,6 +7,7 @@
 pub const foo: _bindgen_ty_1 = _bindgen_ty_1::foo;
 pub const bar: _bindgen_ty_1 = _bindgen_ty_1::bar;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 { foo = 4, bar = 8, }
 pub type EasyToOverflow = ::std::os::raw::c_ulonglong;
diff --git a/tests/expectations/tests/libclang-3.9/constant-evaluate.rs b/tests/expectations/tests/libclang-3.9/constant-evaluate.rs
index 096bc1822f..76cbf24edf 100644
--- a/tests/expectations/tests/libclang-3.9/constant-evaluate.rs
+++ b/tests/expectations/tests/libclang-3.9/constant-evaluate.rs
@@ -7,6 +7,7 @@
 pub const foo: _bindgen_ty_1 = _bindgen_ty_1::foo;
 pub const bar: _bindgen_ty_1 = _bindgen_ty_1::bar;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     foo = 4,
diff --git a/tests/expectations/tests/libclang-4/constant-evaluate.rs b/tests/expectations/tests/libclang-4/constant-evaluate.rs
index 096bc1822f..76cbf24edf 100644
--- a/tests/expectations/tests/libclang-4/constant-evaluate.rs
+++ b/tests/expectations/tests/libclang-4/constant-evaluate.rs
@@ -7,6 +7,7 @@
 pub const foo: _bindgen_ty_1 = _bindgen_ty_1::foo;
 pub const bar: _bindgen_ty_1 = _bindgen_ty_1::bar;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_1 {
     foo = 4,
diff --git a/tests/expectations/tests/nsStyleAutoArray.rs b/tests/expectations/tests/nsStyleAutoArray.rs
index 0c9f1ec618..199222ecb7 100644
--- a/tests/expectations/tests/nsStyleAutoArray.rs
+++ b/tests/expectations/tests/nsStyleAutoArray.rs
@@ -23,6 +23,7 @@ pub struct nsStyleAutoArray<T> {
     pub _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
 }
 #[repr(i32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum nsStyleAutoArray_WithSingleInitialElement {
     WITH_SINGLE_INITIAL_ELEMENT = 0,
diff --git a/tests/expectations/tests/overflowed_enum.rs b/tests/expectations/tests/overflowed_enum.rs
index 0e8700dc56..9104867d52 100644
--- a/tests/expectations/tests/overflowed_enum.rs
+++ b/tests/expectations/tests/overflowed_enum.rs
@@ -5,6 +5,7 @@
 
 
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Foo {
     BAP_ARM = 9698489,
@@ -12,6 +13,7 @@ pub enum Foo {
     BAP_X86_64 = 3128633167,
 }
 #[repr(u16)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Bar {
     One = 1,
diff --git a/tests/expectations/tests/prepend-enum-constified-variant.rs b/tests/expectations/tests/prepend-enum-constified-variant.rs
index df9ecf3cda..afe2c0b1f8 100644
--- a/tests/expectations/tests/prepend-enum-constified-variant.rs
+++ b/tests/expectations/tests/prepend-enum-constified-variant.rs
@@ -6,6 +6,7 @@
 
 pub const AV_CODEC_ID_TTF: AVCodecID = AVCodecID::AV_CODEC_ID_FIRST_UNKNOWN;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum AVCodecID {
     AV_CODEC_ID_FIRST_UNKNOWN = 98304,
diff --git a/tests/expectations/tests/short-enums.rs b/tests/expectations/tests/short-enums.rs
index c3b26da93a..882b368c63 100644
--- a/tests/expectations/tests/short-enums.rs
+++ b/tests/expectations/tests/short-enums.rs
@@ -5,16 +5,19 @@
 
 
 #[repr(u8)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum one_byte_t {
     SOME_VALUE = 1,
 }
 #[repr(u16)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum two_byte_t {
     SOME_OTHER_VALUE = 256,
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum four_byte_t {
     SOME_BIGGER_VALUE = 16777216,
diff --git a/tests/expectations/tests/struct_typedef.rs b/tests/expectations/tests/struct_typedef.rs
index d153aa0887..0e6151441e 100644
--- a/tests/expectations/tests/struct_typedef.rs
+++ b/tests/expectations/tests/struct_typedef.rs
@@ -68,12 +68,14 @@ impl Default for _bindgen_ty_1 {
 pub type struct_ptr_t = *mut _bindgen_ty_1;
 pub type struct_ptr_ptr_t = *mut *mut _bindgen_ty_1;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum typedef_named_enum {
     ENUM_HAS_NAME = 1,
 }
 pub const ENUM_IS_ANON: _bindgen_ty_2 = _bindgen_ty_2::ENUM_IS_ANON;
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum _bindgen_ty_2 {
     ENUM_IS_ANON = 0,
diff --git a/tests/expectations/tests/struct_typedef_ns.rs b/tests/expectations/tests/struct_typedef_ns.rs
index 42dfbb529a..cbbdaa7b91 100644
--- a/tests/expectations/tests/struct_typedef_ns.rs
+++ b/tests/expectations/tests/struct_typedef_ns.rs
@@ -40,6 +40,7 @@ pub mod root {
             );
         }
         #[repr(u32)]
+        #[repr(C)]
         #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
         pub enum typedef_enum {
             BAR = 1,
@@ -80,6 +81,7 @@ pub mod root {
         pub const _bindgen_mod_id_12_BAR: root::_bindgen_mod_id_12::_bindgen_ty_2 =
             _bindgen_ty_2::BAR;
         #[repr(u32)]
+        #[repr(C)]
         #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
         pub enum _bindgen_ty_2 {
             BAR = 1,
diff --git a/tests/expectations/tests/weird_bitfields.rs b/tests/expectations/tests/weird_bitfields.rs
index 6a4d0589e6..22cd8ea5ac 100644
--- a/tests/expectations/tests/weird_bitfields.rs
+++ b/tests/expectations/tests/weird_bitfields.rs
@@ -84,6 +84,7 @@ where
     }
 }
 #[repr(u32)]
+#[repr(C)]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum nsStyleSVGOpacitySource {
     eStyleSVGOpacitySource_Normal = 0,
diff --git a/tests/headers/empty-enum.h b/tests/headers/empty-enum.h
new file mode 100644
index 0000000000..8b7502e671
--- /dev/null
+++ b/tests/headers/empty-enum.h
@@ -0,0 +1,15 @@
+// bindgen-flags: --rustified-enum '.*Rustified.*' --constified-enum-module '.*Module.*' -- -x c++ --std=c++14
+
+// Constified is default, so no flag for that.
+
+enum EmptyConstified {};
+enum EmptyRustified {};
+enum EmptyModule {};
+
+enum class EmptyClassRustified : char {};
+enum class EmptyClassConstified : char {};
+enum class EmptyClassModule : char {};
+
+enum class ForwardClassRustified : char;
+enum class ForwardClassConstified : char;
+enum class ForwardClassModule : char;