From 858b01d85219c6e8c25efefd3b6bb2aba87a9615 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 4 Apr 2020 16:14:21 -0700
Subject: [PATCH 1/2] Implement FusedIterator for Map iterators

---
 src/map.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/map.rs b/src/map.rs
index 9891d5b..449c453 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -397,6 +397,8 @@ macro_rules! delegate_iterator {
                 self.iter.len()
             }
         }
+
+        impl $($generics)* FusedIterator for $name $($generics)* {}
     }
 }
 

From d13374812226f20c9d194bcf5aa1bcb36f759bd6 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 4 Apr 2020 16:11:58 -0700
Subject: [PATCH 2/2] Implement FusedIterator for StreamDeserializer where
 possible

---
 src/de.rs   | 9 ++++++++-
 src/lib.rs  | 1 +
 src/read.rs | 5 +++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/de.rs b/src/de.rs
index 890a516..3aa8f29 100644
--- a/src/de.rs
+++ b/src/de.rs
@@ -4,7 +4,7 @@ use crate::error::{Error, ErrorCode, Result};
 use crate::lib::str::FromStr;
 use crate::lib::*;
 use crate::number::Number;
-use crate::read::{self, Reference};
+use crate::read::{self, Fused, Reference};
 use serde::de::{self, Expected, Unexpected};
 use serde::{forward_to_deserialize_any, serde_if_integer128};
 
@@ -2181,6 +2181,13 @@ where
     }
 }
 
+impl<'de, R, T> FusedIterator for StreamDeserializer<'de, R, T>
+where
+    R: Read<'de> + Fused,
+    T: de::Deserialize<'de>,
+{
+}
+
 //////////////////////////////////////////////////////////////////////////////
 
 fn from_trait<'de, R, T>(read: R) -> Result<T>
diff --git a/src/lib.rs b/src/lib.rs
index a276b38..83a7bad 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -363,6 +363,7 @@ mod lib {
     pub use self::core::default::{self, Default};
     pub use self::core::fmt::{self, Debug, Display};
     pub use self::core::hash::{self, Hash};
+    pub use self::core::iter::FusedIterator;
     pub use self::core::marker::{self, PhantomData};
     pub use self::core::result::{self, Result};
     pub use self::core::{borrow, char, cmp, iter, mem, num, ops, slice, str};
diff --git a/src/read.rs b/src/read.rs
index 01d3068..b8233db 100644
--- a/src/read.rs
+++ b/src/read.rs
@@ -718,6 +718,11 @@ impl<'a> Read<'a> for StrRead<'a> {
 
 //////////////////////////////////////////////////////////////////////////////
 
+/// Marker for whether StreamDeserializer can implement FusedIterator.
+pub trait Fused: private::Sealed {}
+impl<'a> Fused for SliceRead<'a> {}
+impl<'a> Fused for StrRead<'a> {}
+
 // Lookup table of bytes that must be escaped. A value of true at index i means
 // that byte i requires an escape sequence in the input.
 static ESCAPE: [bool; 256] = {