feat(types): mark unused types with marker trait

For some reason, some google APIs define types they never use. We now
mark them, just because we can, to show our superiority ;) ;) ;) :D .

src/mako/lib.rs.mako

@@ -51,7 +51,7 @@ use std::io;
 use std::fs;
 use std::old_io::timer::sleep;
 
-pub use cmn::{MultiPartReader, MethodInfo, Result, CallBuilder, Hub, ReadSeek, Part, ResponseResult, RequestValue, NestedType, Delegate, DefaultDelegate};
+pub use cmn::{MultiPartReader, MethodInfo, Result, CallBuilder, Hub, ReadSeek, Part, ResponseResult, RequestValue, NestedType, Delegate, DefaultDelegate, UnusedType};
 
 
 // ##############

src/mako/lib/util.py

@@ -412,6 +412,9 @@ def schema_markers(s, c, transitive=True):
     if len(c.sta_map.get(s.id, dict())) == 0:
         res.add(PART_MARKER_TRAIT)
 
+    if len(res) == 1 and PART_MARKER_TRAIT in res and len(s.used_by) == 0:
+        res.add('UnusedType')
+
     return sorted(res)
 
 ## -- End Rust TypeSystem -- @}

src/rust/cmn.rs

@@ -29,6 +29,10 @@ pub trait ResponseResult: MarkerTrait {}
 /// Identifies types which are used in API requests.
 pub trait RequestValue: MarkerTrait {}
 
+/// Identifies types which are not actually used by the API
+/// This might be a bug within the google API schema.
+pub trait UnusedType: MarkerTrait {}
+
 /// Identifies types which are only used as part of other types, which 
 /// usually are carrying the `Resource` trait.
 pub trait Part: MarkerTrait {}