Support blocklisting __BindgenBitfieldUnit

bindgen-tests/tests/headers/anon_enum_blocklist.h

@@ -0,0 +1,11 @@
+// bindgen-flags: --blocklist-type "_bindgen_ty_1"
+
+enum {
+  FLAG_X,
+  FLAG_Y,
+};
+
+enum {
+  FLAG_Z,
+  FLAG_W,
+};

bindgen-tests/tests/headers/blocklist_bitfield_unit.h

@@ -0,0 +1,7 @@
+// bindgen-flags: --blocklist-type "__BindgenBitfieldUnit" --raw-line '#[path = "./struct_with_bitfields.rs"] mod bitfields;' --raw-line 'use bitfields::*;'
+struct C {
+  unsigned char x;
+  unsigned b1 : 1;
+  unsigned b2 : 1;
+  unsigned baz;
+};

bindgen/codegen/helpers.rs

@@ -1,5 +1,7 @@
 //! Helpers for code generation that don't need macro expansion.
 
+use proc_macro2::{Ident, Span};
+
 use crate::ir::context::BindgenContext;
 use crate::ir::layout::Layout;
 
@@ -109,10 +111,13 @@ pub(crate) fn integer_type(
     Layout::known_type_for_size(ctx, layout.size)
 }
 
+pub(crate) const BITFIELD_UNIT: &str = "__BindgenBitfieldUnit";
+
 /// Generates a bitfield allocation unit type for a type with the given `Layout`.
 pub(crate) fn bitfield_unit(ctx: &BindgenContext, layout: Layout) -> syn::Type {
     let size = layout.size;
-    let ty = syn::parse_quote! { __BindgenBitfieldUnit<[u8; #size]> };
+    let bitfield_unit_name = Ident::new(BITFIELD_UNIT, Span::call_site());
+    let ty = syn::parse_quote! { #bitfield_unit_name<[u8; #size]> };
 
     if ctx.options().enable_cxx_namespaces {
         return syn::parse_quote! { root::#ty };

bindgen/codegen/mod.rs

@@ -1658,13 +1658,13 @@
 
 /// Compute a fields or structs visibility based on multiple conditions.
 /// 1. If the element was declared public, and we respect such CXX accesses specs
 /// (context option) => By default Public, but this can be overruled by an `annotation`.
 ///
 /// 2. If the element was declared private, and we respect such CXX accesses specs
 /// (context option) => By default Private, but this can be overruled by an `annotation`.
 ///
 /// 3. If we do not respect visibility modifiers, the result depends on the `annotation`,
 /// if any, or the passed `default_kind`.
 ///
 fn compute_visibility(
     ctx: &BindgenContext,
@@ -5017,6 +5017,7 @@
 }
 
 pub(crate) mod utils {
+    use super::helpers::BITFIELD_UNIT;
     use super::serialize::CSerialize;
     use super::{error, CodegenError, CodegenResult, ToRustTyOrOpaque};
     use crate::ir::context::BindgenContext;
@@ -5153,6 +5154,12 @@
         ctx: &BindgenContext,
         result: &mut Vec<proc_macro2::TokenStream>,
     ) {
+        if ctx.options().blocklisted_items.matches(BITFIELD_UNIT) ||
+            ctx.options().blocklisted_types.matches(BITFIELD_UNIT)
+        {
+            return;
+        }
+
         let bitfield_unit_src = include_str!("./bitfield_unit.rs");
         let bitfield_unit_src = if ctx.options().rust_features().min_const_fn {
             Cow::Borrowed(bitfield_unit_src)

book/src/using-bitfields.md

@@ -8,6 +8,11 @@ As Rust does not support bitfields, Bindgen generates a struct for each with the
 * For each contiguous block of bitfields, Bindgen emits an opaque physical field that contains one or more logical bitfields
 * A static constructor  ```new_bitfield_{1, 2, ...}``` with a parameter for each bitfield contained within the opaque physical field.
 
+To keep bindgen from generating the bitfield unit struct, it can be blocklisted like any
+other type, i.e. `--blocklist-type "__BindgenBitfieldUnit"`. This may be useful if
+you want to define a custom implementation, or your generated bindings import a
+pre-existing definition for the bitfield unit type.
+
 ## Bitfield examples
 
 For this discussion, we will use the following C type definitions and functions.