Test repr(C) rustified enums

Add basic testing of repr-c enums assuming input is C++11.

Signed-off-by: Per Larsen <perlarsen@google.com>

Author: Per Larsen

bindgen-tests/tests/expectations/tests/enum-doc-rusty-repr-c.rs

@@ -0,0 +1,19 @@
+// bindgen-flags: --rustified-repr-c-enum ".*" -- -std=c++11 -fshort-enums
+
+typedef enum {
+    SOME_VALUE = 0x1,
+} one_byte_t;
+
+static_assert(sizeof(one_byte_t) == 1, "Short enums should work");
+
+typedef enum {
+    SOME_OTHER_VALUE = 0x100,
+} two_byte_t;
+
+static_assert(sizeof(two_byte_t) == 2, "");
+
+typedef enum {
+    SOME_BIGGER_VALUE = 0x1000000,
+} four_byte_t;
+
+static_assert(sizeof(four_byte_t) == 4, "");

bindgen-tests/tests/expectations/tests/short-enums-repr-c.rs

@@ -4060,6 +4060,49 @@ impl CodeGenerator for Enum {
 
         let item = builder.build(ctx, &enum_rust_ty);
         result.push(item);
+
+        if ctx.options().layout_tests &&
+            matches!(variation, EnumVariation::Rust { repr_c: true, .. })
+        {
+            if let Some(layout) = layout {
+                let compile_time = ctx.options().rust_features().offset_of;
+                let fn_name = if compile_time {
+                    None
+                } else {
+                    let fn_name = format!("bindgen_test_layout_{ident}");
+                    Some(ctx.rust_ident_raw(fn_name))
+                };
+                let prefix = ctx.trait_prefix();
+                let size_of_expr = quote! {
+                    ::#prefix::mem::size_of::<#ident>()
+                };
+                let align_of_expr = quote! {
+                    ::#prefix::mem::align_of::<#ident>()
+                };
+                let size = layout.size;
+                let align = layout.align;
+                let size_of_err = format!("Size of {ident}");
+                let align_of_err = format!("Alignment of {ident}");
+
+                if compile_time {
+                    result.push(quote! {
+                        #[allow(clippy::unnecessary_operation, clippy::identity_op)]
+                        const _: () = {
+                            [#size_of_err][#size_of_expr - #size];
+                            [#align_of_err][#align_of_expr - #align];
+                        };
+                    });
+                } else {
+                    result.push(quote! {
+                        #[test]
+                        fn #fn_name() {
+                            assert_eq!(#size_of_expr, #size, #size_of_err);
+                            assert_eq!(#align_of_expr, #align, #align_of_err);
+                        }
+                    });
+                }
+            }
+        }
     }
 }