From 63561609a6517f0a446d304a6d0191adeda54cfa Mon Sep 17 00:00:00 2001
From: Erick Tryzelaar <erick.tryzelaar@gmail.com>
Date: Sun, 9 Aug 2015 21:42:11 -0700
Subject: [PATCH] Add Error::length_mismatch, Error::type_mismatch, and
 de::Type

This improves error handling to match the needs of msgpack
---
 serde/src/de/impls.rs   | 41 ++++++++++----------
 serde/src/de/mod.rs     | 83 +++++++++++++++++++++++++++++++++--------
 serde/src/de/value.rs   |  4 +-
 serde_json/src/value.rs |  4 +-
 4 files changed, 92 insertions(+), 40 deletions(-)

diff --git a/serde/src/de/impls.rs b/serde/src/de/impls.rs
index 48a194f3..5dd823a2 100644
--- a/serde/src/de/impls.rs
+++ b/serde/src/de/impls.rs
@@ -34,6 +34,7 @@ use de::{
     Error,
     MapVisitor,
     SeqVisitor,
+    Type,
     VariantVisitor,
     Visitor,
 };
@@ -85,7 +86,7 @@ impl Visitor for BoolVisitor {
         match s.trim() {
             "true" => Ok(true),
             "false" => Ok(false),
-            _ => Err(Error::syntax("expected `true` or `false`")),
+            _ => Err(Error::type_mismatch(Type::Bool)),
         }
     }
 }
@@ -101,14 +102,14 @@ impl Deserialize for bool {
 ///////////////////////////////////////////////////////////////////////////////
 
 macro_rules! impl_deserialize_num_method {
-    ($src_ty:ty, $method:ident, $from_method:ident) => {
+    ($src_ty:ty, $method:ident, $from_method:ident, $ty:expr) => {
         #[inline]
         fn $method<E>(&mut self, v: $src_ty) -> Result<T, E>
             where E: Error,
         {
             match FromPrimitive::$from_method(v) {
                 Some(v) => Ok(v),
-                None => Err(Error::syntax("expected a number")),
+                None => Err(Error::type_mismatch($ty)),
             }
         }
     }
@@ -132,24 +133,24 @@ impl<
 > Visitor for PrimitiveVisitor<T> {
     type Value = T;
 
-    impl_deserialize_num_method!(isize, visit_isize, from_isize);
-    impl_deserialize_num_method!(i8, visit_i8, from_i8);
-    impl_deserialize_num_method!(i16, visit_i16, from_i16);
-    impl_deserialize_num_method!(i32, visit_i32, from_i32);
-    impl_deserialize_num_method!(i64, visit_i64, from_i64);
-    impl_deserialize_num_method!(usize, visit_usize, from_usize);
-    impl_deserialize_num_method!(u8, visit_u8, from_u8);
-    impl_deserialize_num_method!(u16, visit_u16, from_u16);
-    impl_deserialize_num_method!(u32, visit_u32, from_u32);
-    impl_deserialize_num_method!(u64, visit_u64, from_u64);
-    impl_deserialize_num_method!(f32, visit_f32, from_f32);
-    impl_deserialize_num_method!(f64, visit_f64, from_f64);
+    impl_deserialize_num_method!(isize, visit_isize, from_isize, Type::Isize);
+    impl_deserialize_num_method!(i8, visit_i8, from_i8, Type::I8);
+    impl_deserialize_num_method!(i16, visit_i16, from_i16, Type::I16);
+    impl_deserialize_num_method!(i32, visit_i32, from_i32, Type::I32);
+    impl_deserialize_num_method!(i64, visit_i64, from_i64, Type::I64);
+    impl_deserialize_num_method!(usize, visit_usize, from_usize, Type::Usize);
+    impl_deserialize_num_method!(u8, visit_u8, from_u8, Type::U8);
+    impl_deserialize_num_method!(u16, visit_u16, from_u16, Type::U16);
+    impl_deserialize_num_method!(u32, visit_u32, from_u32, Type::U32);
+    impl_deserialize_num_method!(u64, visit_u64, from_u64, Type::U64);
+    impl_deserialize_num_method!(f32, visit_f32, from_f32, Type::F32);
+    impl_deserialize_num_method!(f64, visit_f64, from_f64, Type::F64);
 
     #[inline]
     fn visit_str<E>(&mut self, v: &str) -> Result<T, E>
         where E: Error,
     {
-        str::FromStr::from_str(v.trim()).or(Err(Error::syntax("expected a str")))
+        str::FromStr::from_str(v.trim()).or(Err(Error::type_mismatch(Type::Str)))
     }
 }
 
@@ -200,7 +201,7 @@ impl Visitor for CharVisitor {
         let mut iter = v.chars();
         if let Some(v) = iter.next() {
             if iter.next().is_some() {
-                Err(Error::syntax("expected a character"))
+                Err(Error::type_mismatch(Type::Char))
             } else {
                 Ok(v)
             }
@@ -243,7 +244,7 @@ impl Visitor for StringVisitor {
     {
         match str::from_utf8(v) {
             Ok(s) => Ok(s.to_string()),
-            Err(_) => Err(Error::syntax("expected utf8 `&[u8]`")),
+            Err(_) => Err(Error::type_mismatch(Type::String)),
         }
     }
 
@@ -252,7 +253,7 @@ impl Visitor for StringVisitor {
     {
         match String::from_utf8(v) {
             Ok(s) => Ok(s),
-            Err(_) => Err(Error::syntax("expected utf8 `&[u8]`")),
+            Err(_) => Err(Error::type_mismatch(Type::String)),
         }
     }
 }
@@ -900,7 +901,7 @@ impl<T, E> Deserialize for Result<T, E> where T: Deserialize, E: Deserialize {
                             _ => {
                                 match str::from_utf8(value) {
                                     Ok(value) => Err(Error::unknown_field(value)),
-                                    Err(_) => Err(Error::syntax("expected a `&[u8]`")),
+                                    Err(_) => Err(Error::type_mismatch(Type::String)),
                                 }
                             }
                         }
diff --git a/serde/src/de/mod.rs b/serde/src/de/mod.rs
index db83bdc2..9e894d5d 100644
--- a/serde/src/de/mod.rs
+++ b/serde/src/de/mod.rs
@@ -5,16 +5,67 @@ pub mod value;
 
 ///////////////////////////////////////////////////////////////////////////////
 
-pub trait Error {
+/// `Error` is a trait that allows a `Deserialize` to generically create a
+/// `Deserializer` error.
+pub trait Error: Sized {
+    /// Raised when there is general error when deserializing a type.
     fn syntax(msg: &str) -> Self;
 
+    /// Raised when a fixed sized sequence or map was passed in the wrong amount of arguments.
+    fn length_mismatch(_len: usize) -> Self {
+        Error::syntax("incorrect length")
+    }
+
+    /// Raised when a `Deserialize` was passed an incorrect type.
+    fn type_mismatch(_type: Type) -> Self {
+        Error::syntax("incorrect type")
+    }
+
+    /// Raised when a `Deserialize` type unexpectedly hit the end of the stream.
     fn end_of_stream() -> Self;
 
+    /// Raised when a `Deserialize` struct type received an unexpected struct field.
     fn unknown_field(field: &str) -> Self;
 
+    /// Raised when a `Deserialize` struct type did not receive a field.
     fn missing_field(field: &'static str) -> Self;
 }
 
+/// `Type` represents all the primitive types that can be deserialized. This is used by
+/// `Error::kind_mismatch`.
+pub enum Type {
+    Bool,
+    Usize,
+    U8,
+    U16,
+    U32,
+    U64,
+    Isize,
+    I8,
+    I16,
+    I32,
+    I64,
+    F32,
+    F64,
+    Char,
+    Str,
+    String,
+    Unit,
+    Option,
+    Seq,
+    Map,
+    UnitStruct,
+    NewtypeStruct,
+    TupleStruct,
+    Struct,
+    Tuple,
+    Enum,
+    StructVariant,
+    TupleVariant,
+    UnitVariant,
+    Bytes,
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 pub trait Deserialize {
@@ -304,7 +355,7 @@ pub trait Visitor {
     fn visit_bool<E>(&mut self, _v: bool) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected a bool"))
+        Err(Error::type_mismatch(Type::Bool))
     }
 
     fn visit_isize<E>(&mut self, v: isize) -> Result<Self::Value, E>
@@ -334,7 +385,7 @@ pub trait Visitor {
     fn visit_i64<E>(&mut self, _v: i64) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected a i64"))
+        Err(Error::type_mismatch(Type::I64))
     }
 
     fn visit_usize<E>(&mut self, v: usize) -> Result<Self::Value, E>
@@ -364,7 +415,7 @@ pub trait Visitor {
     fn visit_u64<E>(&mut self, _v: u64) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected a u64"))
+        Err(Error::type_mismatch(Type::U64))
     }
 
     fn visit_f32<E>(&mut self, v: f32) -> Result<Self::Value, E>
@@ -376,7 +427,7 @@ pub trait Visitor {
     fn visit_f64<E>(&mut self, _v: f64) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected a f64"))
+        Err(Error::type_mismatch(Type::F64))
     }
 
     #[inline]
@@ -391,7 +442,7 @@ pub trait Visitor {
     fn visit_str<E>(&mut self, _v: &str) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected a str"))
+        Err(Error::type_mismatch(Type::Str))
     }
 
     #[inline]
@@ -404,7 +455,7 @@ pub trait Visitor {
     fn visit_unit<E>(&mut self) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected a unit"))
+        Err(Error::type_mismatch(Type::Unit))
     }
 
     #[inline]
@@ -417,37 +468,37 @@ pub trait Visitor {
     fn visit_none<E>(&mut self) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected an Option::None"))
+        Err(Error::type_mismatch(Type::Option))
     }
 
     fn visit_some<D>(&mut self, _deserializer: &mut D) -> Result<Self::Value, D::Error>
         where D: Deserializer,
     {
-        Err(Error::syntax("expected an Option::Some"))
+        Err(Error::type_mismatch(Type::Option))
     }
 
     fn visit_newtype_struct<D>(&mut self, _deserializer: &mut D) -> Result<Self::Value, D::Error>
         where D: Deserializer,
     {
-        Err(Error::syntax("expected a newtype struct"))
+        Err(Error::type_mismatch(Type::NewtypeStruct))
     }
 
     fn visit_seq<V>(&mut self, _visitor: V) -> Result<Self::Value, V::Error>
         where V: SeqVisitor,
     {
-        Err(Error::syntax("expected a sequence"))
+        Err(Error::type_mismatch(Type::Seq))
     }
 
     fn visit_map<V>(&mut self, _visitor: V) -> Result<Self::Value, V::Error>
         where V: MapVisitor,
     {
-        Err(Error::syntax("expected a map"))
+        Err(Error::type_mismatch(Type::Map))
     }
 
     fn visit_bytes<E>(&mut self, _v: &[u8]) -> Result<Self::Value, E>
         where E: Error,
     {
-        Err(Error::syntax("expected a &[u8]"))
+        Err(Error::type_mismatch(Type::Bytes))
     }
 
     fn visit_byte_buf<E>(&mut self, v: Vec<u8>) -> Result<Self::Value, E>
@@ -593,7 +644,7 @@ pub trait VariantVisitor {
 
     /// `visit_unit` is called when deserializing a variant with no values.
     fn visit_unit(&mut self) -> Result<(), Self::Error> {
-        Err(Error::syntax("expected a univ variant"))
+        Err(Error::type_mismatch(Type::UnitVariant))
     }
 
     /// `visit_newtype` is called when deserializing a variant with a single value. By default this
@@ -612,7 +663,7 @@ pub trait VariantVisitor {
                       _visitor: V) -> Result<V::Value, Self::Error>
         where V: Visitor
     {
-        Err(Error::syntax("expected a tuple variant"))
+        Err(Error::type_mismatch(Type::TupleVariant))
     }
 
     /// `visit_struct` is called when deserializing a struct-like variant.
@@ -621,7 +672,7 @@ pub trait VariantVisitor {
                        _visitor: V) -> Result<V::Value, Self::Error>
         where V: Visitor
     {
-        Err(Error::syntax("expected a struct variant"))
+        Err(Error::type_mismatch(Type::StructVariant))
     }
 }
 
diff --git a/serde/src/de/value.rs b/serde/src/de/value.rs
index b6c6f0fe..3492a5c1 100644
--- a/serde/src/de/value.rs
+++ b/serde/src/de/value.rs
@@ -261,7 +261,7 @@ impl<I, T> de::SeqVisitor for SeqDeserializer<I>
         if self.len == 0 {
             Ok(())
         } else {
-            Err(de::Error::end_of_stream())
+            Err(de::Error::length_mismatch(self.len))
         }
     }
 
@@ -382,7 +382,7 @@ impl<I, K, V> de::MapVisitor for MapDeserializer<I, K, V>
         if self.len == 0 {
             Ok(())
         } else {
-            Err(de::Error::end_of_stream())
+            Err(de::Error::length_mismatch(self.len))
         }
     }
 
diff --git a/serde_json/src/value.rs b/serde_json/src/value.rs
index 6ebd5cf8..6ef293ad 100644
--- a/serde_json/src/value.rs
+++ b/serde_json/src/value.rs
@@ -843,7 +843,7 @@ impl<'a> de::SeqVisitor for SeqDeserializer<'a> {
         if self.len == 0 {
             Ok(())
         } else {
-            Err(de::Error::end_of_stream())
+            Err(de::Error::length_mismatch(self.len))
         }
     }
 
@@ -888,7 +888,7 @@ impl<'a> de::MapVisitor for MapDeserializer<'a> {
         if self.len == 0 {
             Ok(())
         } else {
-            Err(de::Error::end_of_stream())
+            Err(de::Error::length_mismatch(self.len))
         }
     }