From f05368ed24aab0c74d419d7de6a3d545d1da927d Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Tue, 4 Apr 2017 19:04:47 -0700
Subject: [PATCH] Remove the no_std implementation of collect_str

---
 serde/src/ser/mod.rs     | 13 ++++---------
 serde/src/ser/private.rs |  7 +++++++
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/serde/src/ser/mod.rs b/serde/src/ser/mod.rs
index ad03b61f..fb9ef2dd 100644
--- a/serde/src/ser/mod.rs
+++ b/serde/src/ser/mod.rs
@@ -654,8 +654,9 @@ pub trait Serializer: Sized {
 
     /// Serialize a string produced by an implementation of `Display`.
     ///
-    /// The default implementation returns an error unconditionally when
-    /// compiled with `no_std`.
+    /// Serializers that use `no_std` are required to provide an implementation
+    /// of this method. If no more sensible behavior is possible, the
+    /// implementation is expected to return an error.
     ///
     /// ```rust
     /// # use serde::{Serialize, Serializer};
@@ -676,13 +677,7 @@ pub trait Serializer: Sized {
     /// ```
     #[cfg(not(any(feature = "std", feature = "collections")))]
     fn collect_str<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
-        where T: Display
-    {
-        // TODO https://github.com/serde-rs/serde/issues/805
-        // Remove this impl and force no_std formats to implement collect_str.
-        let _ = value;
-        Err(Error::custom("this no_std format does not support serializing strings with collect_str"))
-    }
+        where T: Display;
 }
 
 /// Returned from `Serializer::serialize_seq` and
diff --git a/serde/src/ser/private.rs b/serde/src/ser/private.rs
index 0297c8ac..6e30cb72 100644
--- a/serde/src/ser/private.rs
+++ b/serde/src/ser/private.rs
@@ -312,4 +312,11 @@ impl<S> Serializer for TaggedSerializer<S>
         try!(map.serialize_key(inner_variant));
         Ok(SerializeStructVariantAsMapValue::new(map, inner_variant, len))
     }
+
+    #[cfg(not(any(feature = "std", feature = "collections")))]
+    fn collect_str<T: ?Sized>(self, _: &T) -> Result<Self::Ok, Self::Error>
+        where T: Display
+    {
+        Err(self.bad_type(Unsupported::String))
+    }
 }