From a38b24136b44618af5e2fff77d822c6d0ad25efc Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 9 Apr 2017 13:35:20 -0700
Subject: [PATCH 1/2] Rename deserialize_struct_field to deserialize_identifier

Because it applies to both struct fields and discriminants of an enum.
---
 serde/src/de/impls.rs   |  4 ++--
 serde/src/de/mod.rs     |  4 ++--
 serde/src/de/value.rs   | 22 +++++++++++-----------
 serde/src/macros.rs     |  8 ++++----
 serde/src/private/de.rs | 14 +++++++-------
 serde_derive/src/de.rs  |  2 +-
 serde_test/src/de.rs    |  4 ++--
 7 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/serde/src/de/impls.rs b/serde/src/de/impls.rs
index 59793812..ffe3291c 100644
--- a/serde/src/de/impls.rs
+++ b/serde/src/de/impls.rs
@@ -1232,7 +1232,7 @@ impl<'de> Deserialize<'de> for Duration {
                     }
                 }
 
-                deserializer.deserialize_struct_field(FieldVisitor)
+                deserializer.deserialize_identifier(FieldVisitor)
             }
         }
 
@@ -1358,7 +1358,7 @@ impl<'de, Idx: Deserialize<'de>> Deserialize<'de> for std::ops::Range<Idx> {
                     }
                 }
 
-                deserializer.deserialize_struct_field(FieldVisitor)
+                deserializer.deserialize_identifier(FieldVisitor)
             }
         }
 
diff --git a/serde/src/de/mod.rs b/serde/src/de/mod.rs
index 453a531b..754fa12e 100644
--- a/serde/src/de/mod.rs
+++ b/serde/src/de/mod.rs
@@ -911,8 +911,8 @@ pub trait Deserializer<'de>: Sized {
         where V: Visitor<'de>;
 
     /// Hint that the `Deserialize` type is expecting the name of a struct
-    /// field.
-    fn deserialize_struct_field<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    /// field or the discriminant of an enum variant.
+    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Self::Error>
         where V: Visitor<'de>;
 
     /// Hint that the `Deserialize` type is expecting an enum value with a
diff --git a/serde/src/de/value.rs b/serde/src/de/value.rs
index 3b157b0c..1323450d 100644
--- a/serde/src/de/value.rs
+++ b/serde/src/de/value.rs
@@ -108,7 +108,7 @@ impl<'de, E> de::Deserializer<'de> for UnitDeserializer<E>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
         seq_fixed_size bytes map unit_struct newtype_struct tuple_struct struct
-        struct_field tuple enum ignored_any byte_buf
+        identifier tuple enum ignored_any byte_buf
     }
 
     fn deserialize<V>(self, visitor: V) -> Result<V::Value, Self::Error>
@@ -155,7 +155,7 @@ macro_rules! primitive_deserializer {
             forward_to_deserialize! {
                 bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit
                 option seq seq_fixed_size bytes map unit_struct newtype_struct
-                tuple_struct struct struct_field tuple enum ignored_any byte_buf
+                tuple_struct struct identifier tuple enum ignored_any byte_buf
             }
 
             fn deserialize<V>(self, visitor: V) -> Result<V::Value, Self::Error>
@@ -208,7 +208,7 @@ impl<'de, E> de::Deserializer<'de> for U32Deserializer<E>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple ignored_any byte_buf
+        struct identifier tuple ignored_any byte_buf
     }
 
     fn deserialize<V>(self, visitor: V) -> Result<V::Value, Self::Error>
@@ -286,7 +286,7 @@ impl<'de, 'a, E> de::Deserializer<'de> for StrDeserializer<'a, E>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple ignored_any byte_buf
+        struct identifier tuple ignored_any byte_buf
     }
 }
 
@@ -351,7 +351,7 @@ impl<'de, E> de::Deserializer<'de> for StringDeserializer<E>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple ignored_any byte_buf
+        struct identifier tuple ignored_any byte_buf
     }
 }
 
@@ -420,7 +420,7 @@ impl<'de, 'a, E> de::Deserializer<'de> for CowStrDeserializer<'a, E>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple ignored_any byte_buf
+        struct identifier tuple ignored_any byte_buf
     }
 }
 
@@ -495,7 +495,7 @@ impl<'de, I, T, E> de::Deserializer<'de> for SeqDeserializer<I, E>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple enum ignored_any byte_buf
+        struct identifier tuple enum ignored_any byte_buf
     }
 }
 
@@ -603,7 +603,7 @@ impl<'de, V_> de::Deserializer<'de> for SeqVisitorDeserializer<V_>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple enum ignored_any byte_buf
+        struct identifier tuple enum ignored_any byte_buf
     }
 }
 
@@ -707,7 +707,7 @@ impl<'de, I, E> de::Deserializer<'de> for MapDeserializer<'de, I, E>
 
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
-        bytes map unit_struct newtype_struct tuple_struct struct struct_field
+        bytes map unit_struct newtype_struct tuple_struct struct identifier
         tuple enum ignored_any byte_buf
     }
 }
@@ -804,7 +804,7 @@ impl<'de, A, B, E> de::Deserializer<'de> for PairDeserializer<A, B, E>
 
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
-        bytes map unit_struct newtype_struct tuple_struct struct struct_field
+        bytes map unit_struct newtype_struct tuple_struct struct identifier
         tuple enum ignored_any byte_buf
     }
 
@@ -945,7 +945,7 @@ impl<'de, V_> de::Deserializer<'de> for MapVisitorDeserializer<V_>
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple enum ignored_any byte_buf
+        struct identifier tuple enum ignored_any byte_buf
     }
 }
 
diff --git a/serde/src/macros.rs b/serde/src/macros.rs
index 5873e1a7..80ababfa 100644
--- a/serde/src/macros.rs
+++ b/serde/src/macros.rs
@@ -89,8 +89,8 @@ macro_rules! forward_to_deserialize_helper {
     (struct) => {
         forward_to_deserialize_method!{deserialize_struct(&'static str, &'static [&'static str])}
     };
-    (struct_field) => {
-        forward_to_deserialize_method!{deserialize_struct_field()}
+    (identifier) => {
+        forward_to_deserialize_method!{deserialize_identifier()}
     };
     (tuple) => {
         forward_to_deserialize_method!{deserialize_tuple(usize)}
@@ -143,7 +143,7 @@ macro_rules! forward_to_deserialize_helper {
 /// #     forward_to_deserialize! {
 /// #         u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
 /// #         seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
-/// #         tuple_struct struct struct_field tuple enum ignored_any
+/// #         tuple_struct struct identifier tuple enum ignored_any
 /// #     }
 /// # }
 /// #
@@ -176,7 +176,7 @@ macro_rules! forward_to_deserialize_helper {
 ///     forward_to_deserialize! {
 ///         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
 ///         seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
-///         tuple_struct struct struct_field tuple enum ignored_any
+///         tuple_struct struct identifier tuple enum ignored_any
 ///     }
 /// }
 /// #
diff --git a/serde/src/private/de.rs b/serde/src/private/de.rs
index f4e95dc6..2d019b42 100644
--- a/serde/src/private/de.rs
+++ b/serde/src/private/de.rs
@@ -52,7 +52,7 @@ pub fn missing_field<'de, V, E>(field: &'static str) -> Result<V, E>
         forward_to_deserialize! {
             bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
             seq_fixed_size bytes byte_buf map unit_struct newtype_struct
-            tuple_struct struct struct_field tuple enum ignored_any
+            tuple_struct struct identifier tuple enum ignored_any
         }
     }
 
@@ -855,7 +855,7 @@ mod content {
         forward_to_deserialize! {
             bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
             seq_fixed_size bytes byte_buf map unit_struct tuple_struct struct
-            struct_field tuple ignored_any
+            identifier tuple ignored_any
         }
     }
 
@@ -996,7 +996,7 @@ mod content {
         forward_to_deserialize! {
             bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
             seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
-            tuple_struct struct struct_field tuple enum ignored_any
+            tuple_struct struct identifier tuple enum ignored_any
         }
     }
 
@@ -1085,7 +1085,7 @@ mod content {
         forward_to_deserialize! {
             bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
             seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
-            tuple_struct struct struct_field tuple enum ignored_any
+            tuple_struct struct identifier tuple enum ignored_any
         }
     }
 
@@ -1202,7 +1202,7 @@ mod content {
         forward_to_deserialize! {
             bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
             seq_fixed_size bytes byte_buf map unit_struct tuple_struct struct
-            struct_field tuple ignored_any
+            identifier tuple ignored_any
         }
     }
 
@@ -1341,7 +1341,7 @@ mod content {
         forward_to_deserialize! {
             bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
             seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
-            tuple_struct struct struct_field tuple enum ignored_any
+            tuple_struct struct identifier tuple enum ignored_any
         }
     }
 
@@ -1430,7 +1430,7 @@ mod content {
         forward_to_deserialize! {
             bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
             seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
-            tuple_struct struct struct_field tuple enum ignored_any
+            tuple_struct struct identifier tuple enum ignored_any
         }
     }
 
diff --git a/serde_derive/src/de.rs b/serde_derive/src/de.rs
index 4c4ffe14..2335cce1 100644
--- a/serde_derive/src/de.rs
+++ b/serde_derive/src/de.rs
@@ -1190,7 +1190,7 @@ fn deserialize_field_visitor(fields: Vec<(String, Ident)>,
                     }
                 }
 
-                _serde::Deserializer::deserialize_struct_field(__deserializer, __FieldVisitor)
+                _serde::Deserializer::deserialize_identifier(__deserializer, __FieldVisitor)
             }
         }
     }
diff --git a/serde_test/src/de.rs b/serde_test/src/de.rs
index fcbb762b..243c8eb6 100644
--- a/serde_test/src/de.rs
+++ b/serde_test/src/de.rs
@@ -78,7 +78,7 @@ impl<'de, 'a> de::Deserializer<'de> for &'a mut Deserializer<'de> {
 
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit
-        seq bytes byte_buf map struct_field ignored_any
+        seq bytes byte_buf map identifier ignored_any
     }
 
     fn deserialize<V>(self, visitor: V) -> Result<V::Value, Error>
@@ -645,6 +645,6 @@ impl<'de> de::Deserializer<'de> for BytesDeserializer {
     forward_to_deserialize! {
         bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
         seq seq_fixed_size bytes map unit_struct newtype_struct tuple_struct
-        struct struct_field tuple enum ignored_any byte_buf
+        struct identifier tuple enum ignored_any byte_buf
     }
 }

From 52e93150e6b26b0fba0b27f3e175e9470ab0e4df Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 9 Apr 2017 13:50:38 -0700
Subject: [PATCH 2/2] Standardize on u32 as the type of a variant index

---
 serde/src/private/macros.rs |  8 ++++----
 serde/src/private/ser.rs    | 32 ++++++++++++++++----------------
 serde/src/ser/mod.rs        |  8 ++++----
 serde_derive/src/ser.rs     | 16 +++++++++++-----
 serde_test/src/ser.rs       |  8 ++++----
 5 files changed, 39 insertions(+), 33 deletions(-)

diff --git a/serde/src/private/macros.rs b/serde/src/private/macros.rs
index 4d40c510..f0e0703a 100644
--- a/serde/src/private/macros.rs
+++ b/serde/src/private/macros.rs
@@ -66,13 +66,13 @@ macro_rules! __serialize_unimplemented_helper {
         __serialize_unimplemented_method!(serialize_unit_struct(&str) -> Ok);
     };
     (unit_variant) => {
-        __serialize_unimplemented_method!(serialize_unit_variant(&str, usize, &str) -> Ok);
+        __serialize_unimplemented_method!(serialize_unit_variant(&str, u32, &str) -> Ok);
     };
     (newtype_struct) => {
         __serialize_unimplemented_method!(serialize_newtype_struct<T>(&str, &T) -> Ok);
     };
     (newtype_variant) => {
-        __serialize_unimplemented_method!(serialize_newtype_variant<T>(&str, usize, &str, &T) -> Ok);
+        __serialize_unimplemented_method!(serialize_newtype_variant<T>(&str, u32, &str, &T) -> Ok);
     };
     (seq) => {
         type SerializeSeq = $crate::ser::Impossible<Self::Ok, Self::Error>;
@@ -91,7 +91,7 @@ macro_rules! __serialize_unimplemented_helper {
     };
     (tuple_variant) => {
         type SerializeTupleVariant = $crate::ser::Impossible<Self::Ok, Self::Error>;
-        __serialize_unimplemented_method!(serialize_tuple_variant(&str, usize, &str, usize) -> SerializeTupleVariant);
+        __serialize_unimplemented_method!(serialize_tuple_variant(&str, u32, &str, usize) -> SerializeTupleVariant);
     };
     (map) => {
         type SerializeMap = $crate::ser::Impossible<Self::Ok, Self::Error>;
@@ -103,7 +103,7 @@ macro_rules! __serialize_unimplemented_helper {
     };
     (struct_variant) => {
         type SerializeStructVariant = $crate::ser::Impossible<Self::Ok, Self::Error>;
-        __serialize_unimplemented_method!(serialize_struct_variant(&str, usize, &str, usize) -> SerializeStructVariant);
+        __serialize_unimplemented_method!(serialize_struct_variant(&str, u32, &str, usize) -> SerializeStructVariant);
     };
 }
 
diff --git a/serde/src/private/ser.rs b/serde/src/private/ser.rs
index c8d09d0b..157d7656 100644
--- a/serde/src/private/ser.rs
+++ b/serde/src/private/ser.rs
@@ -184,7 +184,7 @@ impl<S> Serializer for TaggedSerializer<S>
 
     fn serialize_unit_variant(self,
                               _: &'static str,
-                              _: usize,
+                              _: u32,
                               inner_variant: &'static str)
                               -> Result<Self::Ok, Self::Error> {
         let mut map = try!(self.delegate.serialize_map(Some(2)));
@@ -204,7 +204,7 @@ impl<S> Serializer for TaggedSerializer<S>
 
     fn serialize_newtype_variant<T: ?Sized>(self,
                                             _: &'static str,
-                                            _: usize,
+                                            _: u32,
                                             inner_variant: &'static str,
                                             inner_value: &T)
                                             -> Result<Self::Ok, Self::Error>
@@ -238,7 +238,7 @@ impl<S> Serializer for TaggedSerializer<S>
     #[cfg(not(any(feature = "std", feature = "collections")))]
     fn serialize_tuple_variant(self,
                                _: &'static str,
-                               _: usize,
+                               _: u32,
                                _: &'static str,
                                _: usize)
                                -> Result<Self::SerializeTupleVariant, Self::Error> {
@@ -250,7 +250,7 @@ impl<S> Serializer for TaggedSerializer<S>
     #[cfg(any(feature = "std", feature = "collections"))]
     fn serialize_tuple_variant(self,
                                _: &'static str,
-                               _: usize,
+                               _: u32,
                                inner_variant: &'static str,
                                len: usize)
                                -> Result<Self::SerializeTupleVariant, Self::Error> {
@@ -278,7 +278,7 @@ impl<S> Serializer for TaggedSerializer<S>
     #[cfg(not(any(feature = "std", feature = "collections")))]
     fn serialize_struct_variant(self,
                                 _: &'static str,
-                                _: usize,
+                                _: u32,
                                 _: &'static str,
                                 _: usize)
                                 -> Result<Self::SerializeStructVariant, Self::Error> {
@@ -290,7 +290,7 @@ impl<S> Serializer for TaggedSerializer<S>
     #[cfg(any(feature = "std", feature = "collections"))]
     fn serialize_struct_variant(self,
                                 _: &'static str,
-                                _: usize,
+                                _: u32,
                                 inner_variant: &'static str,
                                 len: usize)
                                 -> Result<Self::SerializeStructVariant, Self::Error> {
@@ -444,18 +444,18 @@ mod content {
 
         Unit,
         UnitStruct(&'static str),
-        UnitVariant(&'static str, usize, &'static str),
+        UnitVariant(&'static str, u32, &'static str),
         NewtypeStruct(&'static str, Box<Content>),
-        NewtypeVariant(&'static str, usize, &'static str, Box<Content>),
+        NewtypeVariant(&'static str, u32, &'static str, Box<Content>),
 
         Seq(Vec<Content>),
         SeqFixedSize(Vec<Content>),
         Tuple(Vec<Content>),
         TupleStruct(&'static str, Vec<Content>),
-        TupleVariant(&'static str, usize, &'static str, Vec<Content>),
+        TupleVariant(&'static str, u32, &'static str, Vec<Content>),
         Map(Vec<(Content, Content)>),
         Struct(&'static str, Vec<(&'static str, Content)>),
-        StructVariant(&'static str, usize, &'static str, Vec<(&'static str, Content)>),
+        StructVariant(&'static str, u32, &'static str, Vec<(&'static str, Content)>),
     }
 
     impl Serialize for Content {
@@ -645,7 +645,7 @@ mod content {
 
         fn serialize_unit_variant(self,
                                 name: &'static str,
-                                variant_index: usize,
+                                variant_index: u32,
                                 variant: &'static str)
                                 -> Result<Content, E> {
             Ok(Content::UnitVariant(name, variant_index, variant))
@@ -660,7 +660,7 @@ mod content {
 
         fn serialize_newtype_variant<T: ?Sized + Serialize>(self,
                                                             name: &'static str,
-                                                            variant_index: usize,
+                                                            variant_index: u32,
                                                             variant: &'static str,
                                                             value: &T)
                                                             -> Result<Content, E> {
@@ -706,7 +706,7 @@ mod content {
 
         fn serialize_tuple_variant(self,
                                 name: &'static str,
-                                variant_index: usize,
+                                variant_index: u32,
                                 variant: &'static str,
                                 len: usize)
                                 -> Result<Self::SerializeTupleVariant, E> {
@@ -737,7 +737,7 @@ mod content {
 
         fn serialize_struct_variant(self,
                                     name: &'static str,
-                                    variant_index: usize,
+                                    variant_index: u32,
                                     variant: &'static str,
                                     len: usize)
                                     -> Result<Self::SerializeStructVariant, E> {
@@ -825,7 +825,7 @@ mod content {
 
     struct SerializeTupleVariant<E> {
         name: &'static str,
-        variant_index: usize,
+        variant_index: u32,
         variant: &'static str,
         fields: Vec<Content>,
         error: PhantomData<E>,
@@ -916,7 +916,7 @@ mod content {
 
     struct SerializeStructVariant<E> {
         name: &'static str,
-        variant_index: usize,
+        variant_index: u32,
         variant: &'static str,
         fields: Vec<(&'static str, Content)>,
         error: PhantomData<E>,
diff --git a/serde/src/ser/mod.rs b/serde/src/ser/mod.rs
index 332bdfab..1a20646a 100644
--- a/serde/src/ser/mod.rs
+++ b/serde/src/ser/mod.rs
@@ -449,7 +449,7 @@ pub trait Serializer: Sized {
     /// ```
     fn serialize_unit_variant(self,
                               name: &'static str,
-                              variant_index: usize,
+                              variant_index: u32,
                               variant: &'static str)
                               -> Result<Self::Ok, Self::Error>;
 
@@ -504,7 +504,7 @@ pub trait Serializer: Sized {
     /// ```
     fn serialize_newtype_variant<T: ?Sized + Serialize>(self,
                                                         name: &'static str,
-                                                        variant_index: usize,
+                                                        variant_index: u32,
                                                         variant: &'static str,
                                                         value: &T)
                                                         -> Result<Self::Ok, Self::Error>;
@@ -686,7 +686,7 @@ pub trait Serializer: Sized {
     /// ```
     fn serialize_tuple_variant(self,
                                name: &'static str,
-                               variant_index: usize,
+                               variant_index: u32,
                                variant: &'static str,
                                len: usize)
                                -> Result<Self::SerializeTupleVariant, Self::Error>;
@@ -806,7 +806,7 @@ pub trait Serializer: Sized {
     /// ```
     fn serialize_struct_variant(self,
                                 name: &'static str,
-                                variant_index: usize,
+                                variant_index: u32,
                                 variant: &'static str,
                                 len: usize)
                                 -> Result<Self::SerializeStructVariant, Self::Error>;
diff --git a/serde_derive/src/ser.rs b/serde_derive/src/ser.rs
index 51826928..d7d05dc4 100644
--- a/serde_derive/src/ser.rs
+++ b/serde_derive/src/ser.rs
@@ -6,6 +6,8 @@ use fragment::{Fragment, Stmts, Match};
 use internals::ast::{Body, Field, Item, Style, Variant};
 use internals::{self, attr};
 
+use std::u32;
+
 pub fn expand_derive_serialize(item: &syn::DeriveInput) -> Result<Tokens, String> {
     let ctxt = internals::Ctxt::new();
     let item = Item::from_ast(&ctxt, item);
@@ -149,6 +151,8 @@ fn serialize_struct(ident: &syn::Ident,
                     fields: &[Field],
                     item_attrs: &attr::Item)
                     -> Fragment {
+    assert!(fields.len() as u64 <= u32::MAX as u64);
+
     let serialize_fields =
         serialize_struct_visitor(ident,
                                  fields,
@@ -187,13 +191,15 @@ fn serialize_item_enum(ident: &syn::Ident,
                        variants: &[Variant],
                        item_attrs: &attr::Item)
                        -> Fragment {
+    assert!(variants.len() as u64 <= u32::MAX as u64);
+
     let arms: Vec<_> = variants.iter()
         .enumerate()
         .map(|(variant_index, variant)| {
             serialize_variant(ident,
                               generics,
                               variant,
-                              variant_index,
+                              variant_index as u32,
                               item_attrs)
         })
         .collect();
@@ -208,7 +214,7 @@ fn serialize_item_enum(ident: &syn::Ident,
 fn serialize_variant(ident: &syn::Ident,
                      generics: &syn::Generics,
                      variant: &Variant,
-                     variant_index: usize,
+                     variant_index: u32,
                      item_attrs: &attr::Item)
                      -> Tokens {
     let variant_ident = variant.ident.clone();
@@ -292,7 +298,7 @@ fn serialize_variant(ident: &syn::Ident,
 fn serialize_externally_tagged_variant(ident: &syn::Ident,
                                        generics: &syn::Generics,
                                        variant: &Variant,
-                                       variant_index: usize,
+                                       variant_index: u32,
                                        item_attrs: &attr::Item)
                                        -> Fragment {
     let type_name = item_attrs.name().serialize_name();
@@ -538,7 +544,7 @@ fn serialize_untagged_variant(ident: &syn::Ident,
 enum TupleVariant {
     ExternallyTagged {
         type_name: String,
-        variant_index: usize,
+        variant_index: u32,
         variant_name: String,
     },
     Untagged,
@@ -589,7 +595,7 @@ fn serialize_tuple_variant(context: TupleVariant,
 
 enum StructVariant<'a> {
     ExternallyTagged {
-        variant_index: usize,
+        variant_index: u32,
         variant_name: String,
     },
     InternallyTagged { tag: &'a str, variant_name: String },
diff --git a/serde_test/src/ser.rs b/serde_test/src/ser.rs
index 2a82970f..f6c401ee 100644
--- a/serde_test/src/ser.rs
+++ b/serde_test/src/ser.rs
@@ -146,7 +146,7 @@ impl<'s, 'a> ser::Serializer for &'s mut Serializer<'a> {
 
     fn serialize_unit_variant(self,
                               name: &'static str,
-                              _variant_index: usize,
+                              _variant_index: u32,
                               variant: &'static str)
                               -> Result<(), Error> {
         if self.tokens.first() == Some(&Token::Enum(name)) {
@@ -168,7 +168,7 @@ impl<'s, 'a> ser::Serializer for &'s mut Serializer<'a> {
 
     fn serialize_newtype_variant<T: ?Sized>(self,
                                             name: &'static str,
-                                            _variant_index: usize,
+                                            _variant_index: u32,
                                             variant: &'static str,
                                             value: &T)
                                             -> Result<(), Error>
@@ -217,7 +217,7 @@ impl<'s, 'a> ser::Serializer for &'s mut Serializer<'a> {
 
     fn serialize_tuple_variant(self,
                                name: &'static str,
-                               _variant_index: usize,
+                               _variant_index: u32,
                                variant: &'static str,
                                len: usize)
                                -> Result<Self, Error> {
@@ -237,7 +237,7 @@ impl<'s, 'a> ser::Serializer for &'s mut Serializer<'a> {
 
     fn serialize_struct_variant(self,
                                 name: &'static str,
-                                _variant_index: usize,
+                                _variant_index: u32,
                                 variant: &'static str,
                                 len: usize)
                                 -> Result<Self, Error> {