Add ParseCallbacks method to override enum type representation

bindgen-tests/tests/headers/enum-default-bitfield.h

@@ -1,3 +1,4 @@
 // bindgen-flags: --default-enum-style=bitfield --constified-enum-module=Neg
+// bindgen-parse-callbacks: enum-type-changer
 
 #include "enum.h"

bindgen-tests/tests/headers/enum-default-consts.h

@@ -1,3 +1,4 @@
 // bindgen-flags: --default-enum-style=consts --constified-enum-module=Neg
+// bindgen-parse-callbacks: enum-type-changer
 
 #include "enum.h"

bindgen-tests/tests/headers/enum-default-module.h

@@ -1,3 +1,4 @@
 // bindgen-flags: --default-enum-style=moduleconsts --constified-enum-module=Neg
+// bindgen-parse-callbacks: enum-type-changer
 
 #include "enum.h"

bindgen-tests/tests/headers/enum-default-rust.h

@@ -1,3 +1,4 @@
 // bindgen-flags: --default-enum-style=rust --constified-enum-module=Neg
+// bindgen-parse-callbacks: enum-type-changer
 
 #include "enum.h"

bindgen-tests/tests/headers/enum-no-debug-rust.h

@@ -1,3 +1,4 @@
 // bindgen-flags: --no-derive-debug --default-enum-style=rust --constified-enum-module=Neg
+// bindgen-parse-callbacks: enum-type-changer
 
 #include "enum.h"

bindgen-tests/tests/headers/enum.h

@@ -28,4 +28,19 @@ enum NoDebug {
 enum Debug {
     Debug1,
     Debug2,
-};
+};
+
+enum should_be_u8 {
+    FirstU8,
+    SecondU8,
+};
+
+enum should_be_u16 {
+    FirstU16,
+    SecondU16,
+};
+
+enum should_be_i32 {
+    FirstI32,
+    SecondI32,
+};

bindgen-tests/tests/parse_callbacks/mod.rs

@@ -94,6 +94,20 @@ impl ParseCallbacks for StructFieldRename {
     }
 }
 
+#[derive(Debug)]
+struct EnumTypeChanger;
+
+impl ParseCallbacks for EnumTypeChanger {
+    fn enum_type_override(&self, enum_name: &str) -> Option<IntKind> {
+        match enum_name {
+            "should_be_u8" => Some(IntKind::U8),
+            "should_be_u16" => Some(IntKind::U16),
+            "should_be_i32" => Some(IntKind::I32),
+            _ => None,
+        }
+    }
+}
+
 #[derive(Debug)]
 struct BlocklistedTypeImplementsTrait;
 
@@ -191,6 +205,7 @@ pub fn lookup(cb: &str) -> Box<dyn ParseCallbacks> {
         "wrap-as-variadic-fn" => Box::new(WrapAsVariadicFn),
         "type-visibility" => Box::new(TypeVisibility),
         "operator-rename" => Box::new(OperatorRename),
+        "enum-type-changer" => Box::new(EnumTypeChanger),
         call_back => {
             if let Some(prefix) =
                 call_back.strip_prefix("remove-function-prefix-")

bindgen/callbacks.rs

@@ -73,6 +73,12 @@ pub trait ParseCallbacks: fmt::Debug {
     /// the expansion of the macro as a sequence of tokens.
     fn func_macro(&self, _name: &str, _value: &[&[u8]]) {}
 
+    /// The integer kind an enum should have, given the name of the enum type,
+    /// or `None` if you want the default to be chosen.
+    fn enum_type_override(&self, _enum_name: &str) -> Option<IntKind> {
+        None
+    }
+
     /// This function should return whether, given an enum variant
     /// name, and value, this enum variant will forcibly be a constant.
     fn enum_variant_behavior(

bindgen/codegen/mod.rs

@@ -3759,7 +3759,7 @@ impl CodeGenerator for Enum {
         let variation = self.computed_enum_variation(ctx, item);
 
         let repr_translated;
-        let repr = match self.repr().map(|repr| ctx.resolve_type(repr)) {
+        let mut repr = match self.repr().map(|repr| ctx.resolve_type(repr)) {
             Some(repr)
                 if !ctx.options().translate_enum_integer_types &&
                     !variation.is_rust() =>
@@ -3906,6 +3906,18 @@ impl CodeGenerator for Enum {
             });
         }
 
+        let repr_from_callback;
+        if !ctx.options().parse_callbacks.is_empty() {
+            if let Some(callback_type) = ctx
+                .options()
+                .last_callback(|cb| cb.enum_type_override(&name))
+            {
+                repr_from_callback =
+                    Type::new(None, None, TypeKind::Int(callback_type), false);
+                repr = &repr_from_callback;
+            }
+        }
+
         let repr = repr.to_rust_ty_or_opaque(ctx, item);
         let has_typedef = ctx.is_enum_typedef_combo(item.id());