Escape method fragments that happen to be rust keywords (#2359)

Author: pvdrz

bindgen-tests/tests/expectations/tests/objc_escape.rs

@@ -0,0 +1,6 @@
+// bindgen-flags: -- -x objective-c
+// bindgen-osx-only
+
+@interface A
+-(void)f:(int)arg1 as:(int)arg2;
+@end

bindgen-tests/tests/headers/objc_escape.h

@@ -261,7 +261,17 @@ impl ObjCMethod {
                 if name.is_empty() {
                     None
                 } else {
-                    Some(Ident::new(name, Span::call_site()))
+                    // Try to parse the current name as an identifier. This might fail if the
+                    // name is a keyword so we try to prepend "r#" to it and parse again. If
+                    // this also fails, we panic with the first error.
+                    Some(
+                        syn::parse_str::<Ident>(name)
+                            .or_else(|err| {
+                                syn::parse_str::<Ident>(&format!("r#{}", name))
+                                    .map_err(|_| err)
+                            })
+                            .expect("Invalid identifier"),
+                    )
                 }
             })
             .collect();