Implement cli option for custom derive

closes rust-lang#2170

bindgen-cli/options.rs

@@ -225,6 +225,24 @@ where
                     "Create PartialEq implementation, if it can not be derived \
                      automatically.",
                 ),
+            Arg::new("with-derive-custom")
+                .long("with-derive-custom")
+                .help(
+                    "Derive custom traits on any type. \
+                     Don't use with --with-derive-custom-struct.",
+                )
+                .value_name("trait")
+                .multiple_occurrences(true)
+                .number_of_values(1),
+            Arg::new("with-derive-custom-struct")
+                .long("with-derive-custom-struct")
+                .help(
+                    "Derive custom traits on any struct.\
+                     Don't use with --with-derive-custom.",
+                )
+                .value_name("trait")
+                .multiple_occurrences(true)
+                .number_of_values(1),
             Arg::new("with-derive-default")
                 .long("with-derive-default")
                 .help("Derive Default on any type."),
@@ -744,6 +762,36 @@ where
         builder = builder.impl_partialeq(true);
     }
 
+    if let Some(traits) = matches.values_of("with-derive-custom") {
+        #[derive(Debug)]
+        struct CustomTraitCallback {
+            derives: Vec<String>
+        }
+        impl bindgen::callbacks::ParseCallbacks for CustomTraitCallback {
+            fn add_derives(&self, _name: &str) -> Vec<String> {
+                self.derives.to_owned()
+            }
+        }
+
+        let derives: Vec<String> = traits.into_iter().map(|t| t.to_string()).collect();
+        builder = builder.parse_callbacks(Box::new(CustomTraitCallback { derives }));
+    }
+
+    if let Some(traits) = matches.values_of("with-derive-custom-struct") {
+        #[derive(Debug)]
+        struct CustomTraitCallback {
+            derives: Vec<String>
+        }
+        impl bindgen::callbacks::ParseCallbacks for CustomTraitCallback {
+            fn add_derives_struct(&self, _name: &str) -> Vec<String> {
+                self.derives.to_owned()
+            }
+        }
+
+        let derives: Vec<String> = traits.into_iter().map(|t| t.to_string()).collect();
+        builder = builder.parse_callbacks(Box::new(CustomTraitCallback { derives }));
+    }
+
     if matches.is_present("with-derive-default") {
         builder = builder.derive_default(true);
     }

bindgen/callbacks.rs

@@ -1,5 +1,6 @@
 //! A public API for more fine-grained customization of bindgen behavior.
 
+
 pub use crate::ir::analysis::DeriveTrait;
 pub use crate::ir::derive::CanDerive as ImplementsTrait;
 pub use crate::ir::enum_ty::{EnumVariantCustomBehavior, EnumVariantValue};
@@ -108,4 +109,12 @@ pub trait ParseCallbacks: fmt::Debug {
     fn add_derives(&self, _name: &str) -> Vec<String> {
         vec![]
     }
+
+    /// Provide a list of custom derive attributes.
+    ///
+    /// If no additional attributes are wanted, this function should return an
+    /// empty `Vec`.
+    fn add_derives_struct(&self, _name: &str) -> Vec<String> {
+        vec![]
+    }
 }

bindgen/codegen/mod.rs

@@ -2113,10 +2113,14 @@ impl CodeGenerator for CompInfo {
         // The custom derives callback may return a list of derive attributes;
         // add them to the end of the list.
         let custom_derives;
+        let custom_ident_derives;
         if let Some(cb) = &ctx.options().parse_callbacks {
             custom_derives = cb.add_derives(&canonical_name);
             // In most cases this will be a no-op, since custom_derives will be empty.
             derives.extend(custom_derives.iter().map(|s| s.as_str()));
+
+            custom_ident_derives = cb.add_derives_struct(&canonical_name);
+            derives.extend(custom_ident_derives.iter().map(|s| s.as_str()));
         };
 
         if !derives.is_empty() {