From c9cab490f7a3c1038fb5d5bc93d87737228300f8 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Tue, 27 Feb 2024 22:37:04 -0800
Subject: [PATCH] Resolve multiple_bound_locations clippy lint

    warning: bound is defined in more than one place
      --> serde/src/ser/fmt.rs:77:33
       |
    77 |     fn serialize_newtype_struct<T: ?Sized>(self, _name: &'static str, value: &T) -> fmt::Result
       |                                 ^
    78 |     where
    79 |         T: Serialize,
       |         ^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations
       = note: `-W clippy::multiple-bound-locations` implied by `-W clippy::all`
       = help: to override `-W clippy::all` add `#[allow(clippy::multiple_bound_locations)]`

    warning: bound is defined in more than one place
      --> serde/src/ser/fmt.rs:92:23
       |
    92 |     fn serialize_some<T: ?Sized>(self, _value: &T) -> fmt::Result
       |                       ^
    93 |     where
    94 |         T: Serialize,
       |         ^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/fmt.rs:103:34
        |
    103 |     fn serialize_newtype_variant<T: ?Sized>(
        |                                  ^
    ...
    111 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/fmt.rs:164:20
        |
    164 |     fn collect_str<T: ?Sized>(self, value: &T) -> fmt::Result
        |                    ^
    165 |     where
    166 |         T: Display,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
      --> serde/src/ser/impossible.rs:75:26
       |
    75 |     fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
       |                          ^
    76 |     where
    77 |         T: Serialize,
       |         ^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
      --> serde/src/ser/impossible.rs:95:26
       |
    95 |     fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
       |                          ^
    96 |     where
    97 |         T: Serialize,
       |         ^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/impossible.rs:115:24
        |
    115 |     fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        |                        ^
    116 |     where
    117 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/impossible.rs:135:24
        |
    135 |     fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        |                        ^
    136 |     where
    137 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/impossible.rs:155:22
        |
    155 |     fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Error>
        |                      ^
    156 |     where
    157 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/impossible.rs:163:24
        |
    163 |     fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        |                        ^
    164 |     where
    165 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/impossible.rs:183:24
        |
    183 |     fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
        |                        ^
    184 |     where
    185 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/impossible.rs:204:24
        |
    204 |     fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
        |                        ^
    205 |     where
    206 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/mod.rs:799:23
        |
    799 |     fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
        |                       ^
    800 |     where
    801 |         T: Serialize;
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/mod.rs:894:33
        |
    894 |     fn serialize_newtype_struct<T: ?Sized>(
        |                                 ^
    ...
    900 |         T: Serialize;
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/ser/mod.rs:928:34
        |
    928 |     fn serialize_newtype_variant<T: ?Sized>(
        |                                  ^
    ...
    936 |         T: Serialize;
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1349:20
         |
    1349 |     fn collect_str<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
         |                    ^
    1350 |     where
    1351 |         T: Display,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1496:26
         |
    1496 |     fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
         |                          ^
    1497 |     where
    1498 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1596:26
         |
    1596 |     fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
         |                          ^
    1597 |     where
    1598 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1641:24
         |
    1641 |     fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
         |                        ^
    1642 |     where
    1643 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1699:24
         |
    1699 |     fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
         |                        ^
    1700 |     where
    1701 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1770:22
         |
    1770 |     fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Self::Error>
         |                      ^
    1771 |     where
    1772 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1780:24
         |
    1780 |     fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
         |                        ^
    1781 |     where
    1782 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1801:24
         |
    1801 |     fn serialize_entry<K: ?Sized, V: ?Sized>(
         |                        ^
    ...
    1807 |         K: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1801:35
         |
    1801 |     fn serialize_entry<K: ?Sized, V: ?Sized>(
         |                                   ^
    ...
    1808 |         V: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1859:24
         |
    1859 |     fn serialize_field<T: ?Sized>(
         |                        ^
    ...
    1865 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/ser/mod.rs:1925:24
         |
    1925 |     fn serialize_field<T: ?Sized>(
         |                        ^
    ...
    1931 |         T: Serialize;
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:177:23
        |
    177 |     fn serialize_some<T: ?Sized>(self, _: &T) -> Result<Self::Ok, Self::Error>
        |                       ^
    178 |     where
    179 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:208:33
        |
    208 |     fn serialize_newtype_struct<T: ?Sized>(
        |                                 ^
    ...
    214 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:219:34
        |
    219 |     fn serialize_newtype_variant<T: ?Sized>(
        |                                  ^
    ...
    227 |         T: Serialize,
        |         ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:367:28
        |
    367 |         fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), M::Error>
        |                            ^
    368 |         where
    369 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:407:28
        |
    407 |         fn serialize_field<T: ?Sized>(
        |                            ^
    ...
    413 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:638:27
        |
    638 |         fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Content, E>
        |                           ^
    639 |         where
    640 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:662:37
        |
    662 |         fn serialize_newtype_struct<T: ?Sized>(
        |                                     ^
    ...
    668 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:676:38
        |
    676 |         fn serialize_newtype_variant<T: ?Sized>(
        |                                      ^
    ...
    684 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:785:30
        |
    785 |         fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
        |                              ^
    786 |         where
    787 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:811:30
        |
    811 |         fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
        |                              ^
    812 |         where
    813 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:838:28
        |
    838 |         fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
        |                            ^
    839 |         where
    840 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:867:28
        |
    867 |         fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
        |                            ^
    868 |         where
    869 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:899:26
        |
    899 |         fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), E>
        |                          ^
    900 |         where
    901 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:908:28
        |
    908 |         fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
        |                            ^
    909 |         where
    910 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:925:28
        |
    925 |         fn serialize_entry<K: ?Sized, V: ?Sized>(&mut self, key: &K, value: &V) -> Result<(), E>
        |                            ^
    926 |         where
    927 |             K: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:925:39
        |
    925 |         fn serialize_entry<K: ?Sized, V: ?Sized>(&mut self, key: &K, value: &V) -> Result<(), E>
        |                                       ^
    ...
    928 |             V: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:950:28
        |
    950 |         fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), E>
        |                            ^
    951 |         where
    952 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
       --> serde/src/private/ser.rs:979:28
        |
    979 |         fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), E>
        |                            ^
    980 |         where
    981 |             T: Serialize,
        |             ^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1091:23
         |
    1091 |     fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
         |                       ^
    1092 |     where
    1093 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1115:33
         |
    1115 |     fn serialize_newtype_struct<T: ?Sized>(
         |                                 ^
    ...
    1121 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1126:34
         |
    1126 |     fn serialize_newtype_variant<T: ?Sized>(
         |                                  ^
    ...
    1134 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1205:22
         |
    1205 |     fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Self::Error>
         |                      ^
    1206 |     where
    1207 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1212:24
         |
    1212 |     fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
         |                        ^
    1213 |     where
    1214 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1219:24
         |
    1219 |     fn serialize_entry<K: ?Sized, V: ?Sized>(
         |                        ^
    ...
    1225 |         K: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1219:35
         |
    1219 |     fn serialize_entry<K: ?Sized, V: ?Sized>(
         |                                   ^
    ...
    1226 |         V: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1247:24
         |
    1247 |     fn serialize_field<T: ?Sized>(
         |                        ^
    ...
    1253 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1292:24
         |
    1292 |     fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
         |                        ^
    1293 |     where
    1294 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

    warning: bound is defined in more than one place
        --> serde/src/private/ser.rs:1338:24
         |
    1338 |     fn serialize_field<T: ?Sized>(
         |                        ^
    ...
    1344 |         T: Serialize,
         |         ^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations
---
 serde/src/de/impls.rs       |  17 +++--
 serde/src/de/mod.rs         |   8 +--
 serde/src/private/doc.rs    |   5 +-
 serde/src/private/ser.rs    | 132 +++++++++++++++---------------------
 serde/src/ser/fmt.rs        |  16 ++---
 serde/src/ser/impls.rs      |  37 +++++-----
 serde/src/ser/impossible.rs |  32 ++++-----
 serde/src/ser/mod.rs        |  70 ++++++++-----------
 8 files changed, 149 insertions(+), 168 deletions(-)

diff --git a/serde/src/de/impls.rs b/serde/src/de/impls.rs
index 413c997a..c866c90e 100644
--- a/serde/src/de/impls.rs
+++ b/serde/src/de/impls.rs
@@ -852,7 +852,10 @@ struct PhantomDataVisitor<T: ?Sized> {
     marker: PhantomData<T>,
 }
 
-impl<'de, T: ?Sized> Visitor<'de> for PhantomDataVisitor<T> {
+impl<'de, T> Visitor<'de> for PhantomDataVisitor<T>
+where
+    T: ?Sized,
+{
     type Value = PhantomData<T>;
 
     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
@@ -868,7 +871,10 @@ impl<'de, T: ?Sized> Visitor<'de> for PhantomDataVisitor<T> {
     }
 }
 
-impl<'de, T: ?Sized> Deserialize<'de> for PhantomData<T> {
+impl<'de, T> Deserialize<'de> for PhantomData<T>
+where
+    T: ?Sized,
+{
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
@@ -1877,9 +1883,9 @@ forwarded_impl! {
 
 #[cfg(any(feature = "std", feature = "alloc"))]
 #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
-impl<'de, 'a, T: ?Sized> Deserialize<'de> for Cow<'a, T>
+impl<'de, 'a, T> Deserialize<'de> for Cow<'a, T>
 where
-    T: ToOwned,
+    T: ?Sized + ToOwned,
     T::Owned: Deserialize<'de>,
 {
     #[inline]
@@ -1945,8 +1951,9 @@ macro_rules! box_forwarded_impl {
         $t:ident
     ) => {
         $(#[$attr])*
-        impl<'de, T: ?Sized> Deserialize<'de> for $t<T>
+        impl<'de, T> Deserialize<'de> for $t<T>
         where
+            T: ?Sized,
             Box<T>: Deserialize<'de>,
         {
             fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
diff --git a/serde/src/de/mod.rs b/serde/src/de/mod.rs
index 1924fe3d..4c5a5f9b 100644
--- a/serde/src/de/mod.rs
+++ b/serde/src/de/mod.rs
@@ -1735,9 +1735,9 @@ pub trait SeqAccess<'de> {
     }
 }
 
-impl<'de, 'a, A: ?Sized> SeqAccess<'de> for &'a mut A
+impl<'de, 'a, A> SeqAccess<'de> for &'a mut A
 where
-    A: SeqAccess<'de>,
+    A: ?Sized + SeqAccess<'de>,
 {
     type Error = A::Error;
 
@@ -1888,9 +1888,9 @@ pub trait MapAccess<'de> {
     }
 }
 
-impl<'de, 'a, A: ?Sized> MapAccess<'de> for &'a mut A
+impl<'de, 'a, A> MapAccess<'de> for &'a mut A
 where
-    A: MapAccess<'de>,
+    A: ?Sized + MapAccess<'de>,
 {
     type Error = A::Error;
 
diff --git a/serde/src/private/doc.rs b/serde/src/private/doc.rs
index 1b18fe6b..1f17c8db 100644
--- a/serde/src/private/doc.rs
+++ b/serde/src/private/doc.rs
@@ -56,7 +56,10 @@ macro_rules! __serialize_unimplemented {
 #[macro_export]
 macro_rules! __serialize_unimplemented_method {
     ($func:ident $(<$t:ident>)* ($($arg:ty),*) -> $ret:ident) => {
-        fn $func $(<$t: ?Sized + $crate::Serialize>)* (self $(, _: $arg)*) -> $crate::__private::Result<Self::$ret, Self::Error> {
+        fn $func $(<$t>)* (self $(, _: $arg)*) -> $crate::__private::Result<Self::$ret, Self::Error>
+        where
+            $($t: ?Sized + $crate::Serialize,)*
+        {
             unimplemented!()
         }
     };
diff --git a/serde/src/private/ser.rs b/serde/src/private/ser.rs
index 50bcb251..40cc6cbd 100644
--- a/serde/src/private/ser.rs
+++ b/serde/src/private/ser.rs
@@ -174,9 +174,9 @@ where
         Err(self.bad_type(Unsupported::Optional))
     }
 
-    fn serialize_some<T: ?Sized>(self, _: &T) -> Result<Self::Ok, Self::Error>
+    fn serialize_some<T>(self, _: &T) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         Err(self.bad_type(Unsupported::Optional))
     }
@@ -205,18 +205,18 @@ where
         map.end()
     }
 
-    fn serialize_newtype_struct<T: ?Sized>(
+    fn serialize_newtype_struct<T>(
         self,
         _: &'static str,
         value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         value.serialize(self)
     }
 
-    fn serialize_newtype_variant<T: ?Sized>(
+    fn serialize_newtype_variant<T>(
         self,
         _: &'static str,
         _: u32,
@@ -224,7 +224,7 @@ where
         inner_value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let mut map = tri!(self.delegate.serialize_map(Some(2)));
         tri!(map.serialize_entry(self.tag, self.variant_name));
@@ -327,9 +327,9 @@ where
     }
 
     #[cfg(not(any(feature = "std", feature = "alloc")))]
-    fn collect_str<T: ?Sized>(self, _: &T) -> Result<Self::Ok, Self::Error>
+    fn collect_str<T>(self, _: &T) -> Result<Self::Ok, Self::Error>
     where
-        T: Display,
+        T: ?Sized + Display,
     {
         Err(self.bad_type(Unsupported::String))
     }
@@ -364,9 +364,9 @@ mod content {
         type Ok = M::Ok;
         type Error = M::Error;
 
-        fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), M::Error>
+        fn serialize_field<T>(&mut self, value: &T) -> Result<(), M::Error>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<M::Error>::new()));
             self.fields.push(value);
@@ -404,13 +404,9 @@ mod content {
         type Ok = M::Ok;
         type Error = M::Error;
 
-        fn serialize_field<T: ?Sized>(
-            &mut self,
-            key: &'static str,
-            value: &T,
-        ) -> Result<(), M::Error>
+        fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), M::Error>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<M::Error>::new()));
             self.fields.push((key, value));
@@ -635,9 +631,9 @@ mod content {
             Ok(Content::None)
         }
 
-        fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Content, E>
+        fn serialize_some<T>(self, value: &T) -> Result<Content, E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             Ok(Content::Some(Box::new(tri!(value.serialize(self)))))
         }
@@ -659,13 +655,9 @@ mod content {
             Ok(Content::UnitVariant(name, variant_index, variant))
         }
 
-        fn serialize_newtype_struct<T: ?Sized>(
-            self,
-            name: &'static str,
-            value: &T,
-        ) -> Result<Content, E>
+        fn serialize_newtype_struct<T>(self, name: &'static str, value: &T) -> Result<Content, E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             Ok(Content::NewtypeStruct(
                 name,
@@ -673,7 +665,7 @@ mod content {
             ))
         }
 
-        fn serialize_newtype_variant<T: ?Sized>(
+        fn serialize_newtype_variant<T>(
             self,
             name: &'static str,
             variant_index: u32,
@@ -681,7 +673,7 @@ mod content {
             value: &T,
         ) -> Result<Content, E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             Ok(Content::NewtypeVariant(
                 name,
@@ -782,9 +774,9 @@ mod content {
         type Ok = Content;
         type Error = E;
 
-        fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
+        fn serialize_element<T>(&mut self, value: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<E>::new()));
             self.elements.push(value);
@@ -808,9 +800,9 @@ mod content {
         type Ok = Content;
         type Error = E;
 
-        fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
+        fn serialize_element<T>(&mut self, value: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<E>::new()));
             self.elements.push(value);
@@ -835,9 +827,9 @@ mod content {
         type Ok = Content;
         type Error = E;
 
-        fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
+        fn serialize_field<T>(&mut self, value: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<E>::new()));
             self.fields.push(value);
@@ -864,9 +856,9 @@ mod content {
         type Ok = Content;
         type Error = E;
 
-        fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
+        fn serialize_field<T>(&mut self, value: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<E>::new()));
             self.fields.push(value);
@@ -896,18 +888,18 @@ mod content {
         type Ok = Content;
         type Error = E;
 
-        fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), E>
+        fn serialize_key<T>(&mut self, key: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let key = tri!(key.serialize(ContentSerializer::<E>::new()));
             self.key = Some(key);
             Ok(())
         }
 
-        fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), E>
+        fn serialize_value<T>(&mut self, value: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let key = self
                 .key
@@ -922,10 +914,10 @@ mod content {
             Ok(Content::Map(self.entries))
         }
 
-        fn serialize_entry<K: ?Sized, V: ?Sized>(&mut self, key: &K, value: &V) -> Result<(), E>
+        fn serialize_entry<K, V>(&mut self, key: &K, value: &V) -> Result<(), E>
         where
-            K: Serialize,
-            V: Serialize,
+            K: ?Sized + Serialize,
+            V: ?Sized + Serialize,
         {
             let key = tri!(key.serialize(ContentSerializer::<E>::new()));
             let value = tri!(value.serialize(ContentSerializer::<E>::new()));
@@ -947,9 +939,9 @@ mod content {
         type Ok = Content;
         type Error = E;
 
-        fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), E>
+        fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<E>::new()));
             self.fields.push((key, value));
@@ -976,9 +968,9 @@ mod content {
         type Ok = Content;
         type Error = E;
 
-        fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), E>
+        fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), E>
         where
-            T: Serialize,
+            T: ?Sized + Serialize,
         {
             let value = tri!(value.serialize(ContentSerializer::<E>::new()));
             self.fields.push((key, value));
@@ -1088,9 +1080,9 @@ where
         Ok(())
     }
 
-    fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
+    fn serialize_some<T>(self, value: &T) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         value.serialize(self)
     }
@@ -1112,18 +1104,18 @@ where
         Err(Self::bad_type(Unsupported::Enum))
     }
 
-    fn serialize_newtype_struct<T: ?Sized>(
+    fn serialize_newtype_struct<T>(
         self,
         _: &'static str,
         value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         value.serialize(self)
     }
 
-    fn serialize_newtype_variant<T: ?Sized>(
+    fn serialize_newtype_variant<T>(
         self,
         _: &'static str,
         _: u32,
@@ -1131,7 +1123,7 @@ where
         value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         tri!(self.0.serialize_key(variant));
         self.0.serialize_value(value)
@@ -1202,28 +1194,24 @@ where
     type Ok = ();
     type Error = M::Error;
 
-    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Self::Error>
+    fn serialize_key<T>(&mut self, key: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         self.0.serialize_key(key)
     }
 
-    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_value<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         self.0.serialize_value(value)
     }
 
-    fn serialize_entry<K: ?Sized, V: ?Sized>(
-        &mut self,
-        key: &K,
-        value: &V,
-    ) -> Result<(), Self::Error>
+    fn serialize_entry<K, V>(&mut self, key: &K, value: &V) -> Result<(), Self::Error>
     where
-        K: Serialize,
-        V: Serialize,
+        K: ?Sized + Serialize,
+        V: ?Sized + Serialize,
     {
         self.0.serialize_entry(key, value)
     }
@@ -1244,13 +1232,9 @@ where
     type Ok = ();
     type Error = M::Error;
 
-    fn serialize_field<T: ?Sized>(
-        &mut self,
-        key: &'static str,
-        value: &T,
-    ) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         self.0.serialize_entry(key, value)
     }
@@ -1289,9 +1273,9 @@ where
     type Ok = ();
     type Error = M::Error;
 
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let value = tri!(value.serialize(ContentSerializer::<M::Error>::new()));
         self.fields.push(value);
@@ -1335,13 +1319,9 @@ where
     type Ok = ();
     type Error = M::Error;
 
-    fn serialize_field<T: ?Sized>(
-        &mut self,
-        key: &'static str,
-        value: &T,
-    ) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let value = tri!(value.serialize(ContentSerializer::<M::Error>::new()));
         self.fields.push((key, value));
diff --git a/serde/src/ser/fmt.rs b/serde/src/ser/fmt.rs
index 0650ab6f..04684ade 100644
--- a/serde/src/ser/fmt.rs
+++ b/serde/src/ser/fmt.rs
@@ -74,9 +74,9 @@ impl<'a, 'b> Serializer for &'a mut fmt::Formatter<'b> {
         Display::fmt(variant, self)
     }
 
-    fn serialize_newtype_struct<T: ?Sized>(self, _name: &'static str, value: &T) -> fmt::Result
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> fmt::Result
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         Serialize::serialize(value, self)
     }
@@ -89,9 +89,9 @@ impl<'a, 'b> Serializer for &'a mut fmt::Formatter<'b> {
         Err(fmt::Error)
     }
 
-    fn serialize_some<T: ?Sized>(self, _value: &T) -> fmt::Result
+    fn serialize_some<T>(self, _value: &T) -> fmt::Result
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         Err(fmt::Error)
     }
@@ -100,7 +100,7 @@ impl<'a, 'b> Serializer for &'a mut fmt::Formatter<'b> {
         Err(fmt::Error)
     }
 
-    fn serialize_newtype_variant<T: ?Sized>(
+    fn serialize_newtype_variant<T>(
         self,
         _name: &'static str,
         _variant_index: u32,
@@ -108,7 +108,7 @@ impl<'a, 'b> Serializer for &'a mut fmt::Formatter<'b> {
         _value: &T,
     ) -> fmt::Result
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         Err(fmt::Error)
     }
@@ -161,9 +161,9 @@ impl<'a, 'b> Serializer for &'a mut fmt::Formatter<'b> {
         Err(fmt::Error)
     }
 
-    fn collect_str<T: ?Sized>(self, value: &T) -> fmt::Result
+    fn collect_str<T>(self, value: &T) -> fmt::Result
     where
-        T: Display,
+        T: ?Sized + Display,
     {
         Display::fmt(value, self)
     }
diff --git a/serde/src/ser/impls.rs b/serde/src/ser/impls.rs
index 8c70634a..7aa11621 100644
--- a/serde/src/ser/impls.rs
+++ b/serde/src/ser/impls.rs
@@ -114,7 +114,10 @@ where
 
 ////////////////////////////////////////////////////////////////////////////////
 
-impl<T: ?Sized> Serialize for PhantomData<T> {
+impl<T> Serialize for PhantomData<T>
+where
+    T: ?Sized,
+{
     #[inline]
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -504,17 +507,17 @@ macro_rules! deref_impl {
 }
 
 deref_impl! {
-    <'a, T: ?Sized> Serialize for &'a T where T: Serialize
+    <'a, T> Serialize for &'a T where T: ?Sized + Serialize
 }
 
 deref_impl! {
-    <'a, T: ?Sized> Serialize for &'a mut T where T: Serialize
+    <'a, T> Serialize for &'a mut T where T: ?Sized + Serialize
 }
 
 deref_impl! {
     #[cfg(any(feature = "std", feature = "alloc"))]
     #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
-    <T: ?Sized> Serialize for Box<T> where T: Serialize
+    <T> Serialize for Box<T> where T: ?Sized + Serialize
 }
 
 deref_impl! {
@@ -528,7 +531,7 @@ deref_impl! {
     /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
     #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
     #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
-    <T: ?Sized> Serialize for Rc<T> where T: Serialize
+    <T> Serialize for Rc<T> where T: ?Sized + Serialize
 }
 
 deref_impl! {
@@ -542,13 +545,13 @@ deref_impl! {
     /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
     #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
     #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
-    <T: ?Sized> Serialize for Arc<T> where T: Serialize
+    <T> Serialize for Arc<T> where T: ?Sized + Serialize
 }
 
 deref_impl! {
     #[cfg(any(feature = "std", feature = "alloc"))]
     #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
-    <'a, T: ?Sized> Serialize for Cow<'a, T> where T: Serialize + ToOwned
+    <'a, T> Serialize for Cow<'a, T> where T: ?Sized + Serialize + ToOwned
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -561,9 +564,9 @@ deref_impl! {
     doc_cfg,
     doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
 )]
-impl<T: ?Sized> Serialize for RcWeak<T>
+impl<T> Serialize for RcWeak<T>
 where
-    T: Serialize,
+    T: ?Sized + Serialize,
 {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -581,9 +584,9 @@ where
     doc_cfg,
     doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
 )]
-impl<T: ?Sized> Serialize for ArcWeak<T>
+impl<T> Serialize for ArcWeak<T>
 where
-    T: Serialize,
+    T: ?Sized + Serialize,
 {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -641,9 +644,9 @@ where
     }
 }
 
-impl<T: ?Sized> Serialize for RefCell<T>
+impl<T> Serialize for RefCell<T>
 where
-    T: Serialize,
+    T: ?Sized + Serialize,
 {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -658,9 +661,9 @@ where
 
 #[cfg(feature = "std")]
 #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
-impl<T: ?Sized> Serialize for Mutex<T>
+impl<T> Serialize for Mutex<T>
 where
-    T: Serialize,
+    T: ?Sized + Serialize,
 {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -675,9 +678,9 @@ where
 
 #[cfg(feature = "std")]
 #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
-impl<T: ?Sized> Serialize for RwLock<T>
+impl<T> Serialize for RwLock<T>
 where
-    T: Serialize,
+    T: ?Sized + Serialize,
 {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
diff --git a/serde/src/ser/impossible.rs b/serde/src/ser/impossible.rs
index 479be940..6432d577 100644
--- a/serde/src/ser/impossible.rs
+++ b/serde/src/ser/impossible.rs
@@ -72,9 +72,9 @@ where
     type Ok = Ok;
     type Error = Error;
 
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    fn serialize_element<T>(&mut self, value: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = value;
         match self.void {}
@@ -92,9 +92,9 @@ where
     type Ok = Ok;
     type Error = Error;
 
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    fn serialize_element<T>(&mut self, value: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = value;
         match self.void {}
@@ -112,9 +112,9 @@ where
     type Ok = Ok;
     type Error = Error;
 
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    fn serialize_field<T>(&mut self, value: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = value;
         match self.void {}
@@ -132,9 +132,9 @@ where
     type Ok = Ok;
     type Error = Error;
 
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    fn serialize_field<T>(&mut self, value: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = value;
         match self.void {}
@@ -152,17 +152,17 @@ where
     type Ok = Ok;
     type Error = Error;
 
-    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Error>
+    fn serialize_key<T>(&mut self, key: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = key;
         match self.void {}
     }
 
-    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    fn serialize_value<T>(&mut self, value: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = value;
         match self.void {}
@@ -180,9 +180,9 @@ where
     type Ok = Ok;
     type Error = Error;
 
-    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = key;
         let _ = value;
@@ -201,9 +201,9 @@ where
     type Ok = Ok;
     type Error = Error;
 
-    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
     where
-        T: Serialize,
+        T: ?Sized + Serialize,
     {
         let _ = key;
         let _ = value;
diff --git a/serde/src/ser/mod.rs b/serde/src/ser/mod.rs
index 75c45140..715d7e6c 100644
--- a/serde/src/ser/mod.rs
+++ b/serde/src/ser/mod.rs
@@ -796,9 +796,9 @@ pub trait Serializer: Sized {
     /// ```
     ///
     /// [`Some(T)`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.Some
-    fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
+    fn serialize_some<T>(self, value: &T) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Serialize a `()` value.
     ///
@@ -891,13 +891,13 @@ pub trait Serializer: Sized {
     ///     }
     /// }
     /// ```
-    fn serialize_newtype_struct<T: ?Sized>(
+    fn serialize_newtype_struct<T>(
         self,
         name: &'static str,
         value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Serialize a newtype variant like `E::N` in `enum E { N(u8) }`.
     ///
@@ -925,7 +925,7 @@ pub trait Serializer: Sized {
     ///     }
     /// }
     /// ```
-    fn serialize_newtype_variant<T: ?Sized>(
+    fn serialize_newtype_variant<T>(
         self,
         name: &'static str,
         variant_index: u32,
@@ -933,7 +933,7 @@ pub trait Serializer: Sized {
         value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Begin to serialize a variably sized sequence. This call must be
     /// followed by zero or more calls to `serialize_element`, then a call to
@@ -1346,9 +1346,9 @@ pub trait Serializer: Sized {
     /// [`String`]: https://doc.rust-lang.org/std/string/struct.String.html
     /// [`serialize_str`]: #tymethod.serialize_str
     #[cfg(any(feature = "std", feature = "alloc"))]
-    fn collect_str<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
+    fn collect_str<T>(self, value: &T) -> Result<Self::Ok, Self::Error>
     where
-        T: Display,
+        T: ?Sized + Display,
     {
         self.serialize_str(&value.to_string())
     }
@@ -1379,9 +1379,9 @@ pub trait Serializer: Sized {
     /// }
     /// ```
     #[cfg(not(any(feature = "std", feature = "alloc")))]
-    fn collect_str<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
+    fn collect_str<T>(self, value: &T) -> Result<Self::Ok, Self::Error>
     where
-        T: Display;
+        T: ?Sized + Display;
 
     /// Determine whether `Serialize` implementations should serialize in
     /// human-readable form.
@@ -1493,9 +1493,9 @@ pub trait SerializeSeq {
     type Error: Error;
 
     /// Serialize a sequence element.
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_element<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Finish serializing a sequence.
     fn end(self) -> Result<Self::Ok, Self::Error>;
@@ -1593,9 +1593,9 @@ pub trait SerializeTuple {
     type Error: Error;
 
     /// Serialize a tuple element.
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_element<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Finish serializing a tuple.
     fn end(self) -> Result<Self::Ok, Self::Error>;
@@ -1638,9 +1638,9 @@ pub trait SerializeTupleStruct {
     type Error: Error;
 
     /// Serialize a tuple struct field.
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Finish serializing a tuple struct.
     fn end(self) -> Result<Self::Ok, Self::Error>;
@@ -1696,9 +1696,9 @@ pub trait SerializeTupleVariant {
     type Error: Error;
 
     /// Serialize a tuple variant field.
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Finish serializing a tuple variant.
     fn end(self) -> Result<Self::Ok, Self::Error>;
@@ -1767,9 +1767,9 @@ pub trait SerializeMap {
     /// `serialize_entry` instead as it may be implemented more efficiently in
     /// some formats compared to a pair of calls to `serialize_key` and
     /// `serialize_value`.
-    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Self::Error>
+    fn serialize_key<T>(&mut self, key: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Serialize a map value.
     ///
@@ -1777,9 +1777,9 @@ pub trait SerializeMap {
     ///
     /// Calling `serialize_value` before `serialize_key` is incorrect and is
     /// allowed to panic or produce bogus results.
-    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_value<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Serialize a map entry consisting of a key and a value.
     ///
@@ -1798,14 +1798,10 @@ pub trait SerializeMap {
     /// [`Serialize`]: ../trait.Serialize.html
     /// [`serialize_key`]: #tymethod.serialize_key
     /// [`serialize_value`]: #tymethod.serialize_value
-    fn serialize_entry<K: ?Sized, V: ?Sized>(
-        &mut self,
-        key: &K,
-        value: &V,
-    ) -> Result<(), Self::Error>
+    fn serialize_entry<K, V>(&mut self, key: &K, value: &V) -> Result<(), Self::Error>
     where
-        K: Serialize,
-        V: Serialize,
+        K: ?Sized + Serialize,
+        V: ?Sized + Serialize,
     {
         tri!(self.serialize_key(key));
         self.serialize_value(value)
@@ -1856,13 +1852,9 @@ pub trait SerializeStruct {
     type Error: Error;
 
     /// Serialize a struct field.
-    fn serialize_field<T: ?Sized>(
-        &mut self,
-        key: &'static str,
-        value: &T,
-    ) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Indicate that a struct field has been skipped.
     #[inline]
@@ -1922,13 +1914,9 @@ pub trait SerializeStructVariant {
     type Error: Error;
 
     /// Serialize a struct variant field.
-    fn serialize_field<T: ?Sized>(
-        &mut self,
-        key: &'static str,
-        value: &T,
-    ) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize;
+        T: ?Sized + Serialize;
 
     /// Indicate that a struct variant field has been skipped.
     #[inline]