Provide option to get real virtual fn receiver.

bindgen-tests/tests/headers/specific_receiver.hpp

@@ -0,0 +1,7 @@
+// bindgen-flags: --use-specific-virtual-function-receiver --generate-inline-functions -- -x c++ -std=c++14
+
+class Fish {
+public:
+    virtual void swim() {
+    }
+};

bindgen/ir/function.rs

@@ -533,7 +533,10 @@ impl FunctionSig {
             let is_const = is_method && cursor.method_is_const();
             let is_virtual = is_method && cursor.method_is_virtual();
             let is_static = is_method && cursor.method_is_static();
-            if !is_static && !is_virtual {
+            if !is_static &&
+                (!is_virtual ||
+                    ctx.options().use_specific_virtual_function_receiver)
+            {
                 let parent = cursor.semantic_parent();
                 let class = Item::parse(parent, None, ctx)
                     .expect("Expected to parse the class");

bindgen/options/cli.rs

@@ -441,6 +441,9 @@ struct BindgenCommand {
     /// Always output explicit padding fields.
     #[arg(long)]
     explicit_padding: bool,
+    /// Always be specific about the 'receiver' of a virtual function.
+    #[arg(long)]
+    use_specific_virtual_function_receiver: bool,
     /// Use distinct char16_t
     #[arg(long)]
     use_distinct_char16_t: bool,
@@ -632,6 +635,7 @@ where
         translate_enum_integer_types,
         c_naming,
         explicit_padding,
+        use_specific_virtual_function_receiver,
         use_distinct_char16_t,
         vtable_generation,
         sort_semantically,
@@ -930,6 +934,7 @@ where
             translate_enum_integer_types,
             c_naming,
             explicit_padding,
+            use_specific_virtual_function_receiver,
             use_distinct_char16_t,
             vtable_generation,
             sort_semantically,

bindgen/options/mod.rs

@@ -153,6 +153,21 @@ macro_rules! options {
 }
 
 options! {
+    /// Whether to specify the type of a virtual function receiver
+    use_specific_virtual_function_receiver: bool {
+        methods: {
+            /// Normally, virtual functions have void* as their 'this' type.
+            /// If this flag is enabled, override that behavior to indicate a
+            /// pointer of the specific type.
+            /// Disabled by default.
+            pub fn use_specific_virtual_function_receiver(mut self, doit: bool) -> Builder {
+                self.options.use_specific_virtual_function_receiver = doit;
+                self
+            }
+        },
+        as_args: "--use-specific-virtual-function-receiver",
+    },
+
     /// Whether we should distinguish between C++'s 'char16_t' and 'u16'.
     /// The C++ type `char16_t` is its own special type; it's not a typedef
     /// of some other integer (this differs from C).