fix: forward more errors in de::value::Error

When using a `ValueDeserializer` errors produced with the methods
`type_mismatch`, `length_mismatch` and `syntax` were not forwarded
correctly. These methods now store all information in the enum
`de::value::Error`.

serde/src/de/mod.rs

@@ -33,6 +33,7 @@ pub trait Error: Sized {
 
 /// `Type` represents all the primitive types that can be deserialized. This is used by
 /// `Error::kind_mismatch`.
+#[derive(Clone, PartialEq, Eq, Debug)]
 pub enum Type {
     /// Represents a `bool` type.
     Bool,

serde/src/de/value.rs

@@ -22,7 +22,13 @@ use bytes;
 #[derive(Clone, Debug, PartialEq)]
 pub enum Error {
     /// The value had some syntatic error.
-    SyntaxError,
+    SyntaxError(String),
+
+    /// The value had an incorrect type.
+    TypeError(de::Type),
+
+    /// The value had an invalid length.
+    LengthError(usize),
 
     /// EOF while deserializing a value.
     EndOfStreamError,
@@ -35,7 +41,9 @@ pub enum Error {
 }
 
 impl de::Error for Error {
-    fn syntax(_: &str) -> Self { Error::SyntaxError }
+    fn syntax(msg: &str) -> Self { Error::SyntaxError(String::from(msg)) }
+    fn type_mismatch(type_: de::Type) -> Self { Error::TypeError(type_) }
+    fn length_mismatch(len: usize) -> Self { Error::LengthError(len) }
     fn end_of_stream() -> Self { Error::EndOfStreamError }
     fn unknown_field(field: &str) -> Self { Error::UnknownFieldError(String::from(field)) }
     fn missing_field(field: &'static str) -> Self { Error::MissingFieldError(field) }