Avoid using owned String in deserializers (#11764)

## Summary

This is the pattern I see in a variety of crates, and I believe this is
preferred if you don't _need_ an owned `String`, since you can avoid the
allocation. This could be pretty impactful for us?

crates/uv-configuration/src/required_version.rs

@@ -1,3 +1,4 @@
+use std::fmt::Formatter;
 use std::str::FromStr;
 
 use uv_pep440::{Version, VersionSpecifier, VersionSpecifiers, VersionSpecifiersParseError};
@@ -49,8 +50,21 @@ impl schemars::JsonSchema for RequiredVersion {
 
 impl<'de> serde::Deserialize<'de> for RequiredVersion {
     fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        Self::from_str(&s).map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = RequiredVersion;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                RequiredVersion::from_str(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-distribution-filename/src/wheel.rs

@@ -299,8 +299,21 @@ impl<'de> Deserialize<'de> for WheelFilename {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        FromStr::from_str(&s).map_err(de::Error::custom)
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = WheelFilename;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                WheelFilename::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-distribution-types/src/index_name.rs

@@ -58,7 +58,8 @@ impl<'de> serde::de::Deserialize<'de> for IndexName {
     where
         D: serde::de::Deserializer<'de>,
     {
-        IndexName::new(String::deserialize(deserializer)?).map_err(serde::de::Error::custom)
+        let s = String::deserialize(deserializer)?;
+        IndexName::new(s).map_err(serde::de::Error::custom)
     }
 }
 

crates/uv-distribution-types/src/index_url.rs

@@ -171,8 +171,21 @@ impl<'de> serde::de::Deserialize<'de> for IndexUrl {
     where
         D: serde::de::Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        IndexUrl::from_str(&s).map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = IndexUrl;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                IndexUrl::from_str(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-git-types/src/oid.rs

@@ -1,4 +1,4 @@
-use std::fmt::Display;
+use std::fmt::{Display, Formatter};
 use std::str::{self, FromStr};
 
 use thiserror::Error;
@@ -74,8 +74,21 @@ impl<'de> serde::Deserialize<'de> for GitOid {
     where
         D: serde::Deserializer<'de>,
     {
-        let value = String::deserialize(deserializer)?;
+        struct Visitor;
-        GitOid::from_str(&value).map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = GitOid;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                GitOid::from_str(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-normalize/src/extra_name.rs

@@ -48,8 +48,25 @@ impl<'de> Deserialize<'de> for ExtraName {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        Self::from_str(&s).map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = ExtraName;
+
+            fn expecting(&self, f: &mut Formatter) -> fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                ExtraName::from_str(v).map_err(serde::de::Error::custom)
+            }
+
+            fn visit_string<E: serde::de::Error>(self, v: String) -> Result<Self::Value, E> {
+                ExtraName::from_owned(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-normalize/src/group_name.rs

@@ -1,5 +1,3 @@
-use std::fmt;
-use std::fmt::{Display, Formatter};
 use std::str::FromStr;
 use std::sync::LazyLock;
 
@@ -41,8 +39,25 @@ impl<'de> Deserialize<'de> for GroupName {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        Self::from_str(&s).map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = GroupName;
+
+            fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                GroupName::from_str(v).map_err(serde::de::Error::custom)
+            }
+
+            fn visit_string<E: serde::de::Error>(self, v: String) -> Result<Self::Value, E> {
+                GroupName::from_owned(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 
@@ -55,8 +70,8 @@ impl Serialize for GroupName {
     }
 }
 
-impl Display for GroupName {
+impl std::fmt::Display for GroupName {
-    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         self.0.fmt(f)
     }
 }

crates/uv-normalize/src/package_name.rs

@@ -91,8 +91,25 @@ impl<'de> Deserialize<'de> for PackageName {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        Self::from_str(&s).map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = PackageName;
+
+            fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                PackageName::from_str(v).map_err(serde::de::Error::custom)
+            }
+
+            fn visit_string<E: serde::de::Error>(self, v: String) -> Result<Self::Value, E> {
+                PackageName::from_owned(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-pep440/src/version.rs

@@ -1,4 +1,5 @@
 use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
+use std::fmt::Formatter;
 use std::num::NonZero;
 use std::ops::Deref;
 use std::sync::LazyLock;
@@ -725,14 +726,26 @@ impl Version {
     }
 }
 
-/// <https://github.com/serde-rs/serde/issues/1316#issue-332908452>
 impl<'de> Deserialize<'de> for Version {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        FromStr::from_str(&s).map_err(de::Error::custom)
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = Version;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                Version::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-pep440/src/version_specifier.rs

@@ -1,4 +1,5 @@
 use std::cmp::Ordering;
+use std::fmt::Formatter;
 use std::ops::Bound;
 use std::str::FromStr;
 
@@ -161,8 +162,21 @@ impl<'de> Deserialize<'de> for VersionSpecifiers {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        Self::from_str(&s).map_err(de::Error::custom)
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = VersionSpecifiers;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                VersionSpecifiers::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 
@@ -172,7 +186,7 @@ impl Serialize for VersionSpecifiers {
     where
         S: Serializer,
     {
-        serializer.collect_str(
+        serializer.serialize_str(
             &self
                 .iter()
                 .map(ToString::to_string)
@@ -256,14 +270,26 @@ pub struct VersionSpecifier {
     pub(crate) version: Version,
 }
 
-/// <https://github.com/serde-rs/serde/issues/1316#issue-332908452>
 impl<'de> Deserialize<'de> for VersionSpecifier {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        FromStr::from_str(&s).map_err(de::Error::custom)
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = VersionSpecifier;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                VersionSpecifier::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-pep508/src/lib.rs

@@ -186,8 +186,24 @@ impl<'de, T: Pep508Url> Deserialize<'de> for Requirement<T> {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct RequirementVisitor<T>(std::marker::PhantomData<T>);
-        FromStr::from_str(&s).map_err(de::Error::custom)
+
+        impl<T: Pep508Url> serde::de::Visitor<'_> for RequirementVisitor<T> {
+            type Value = Requirement<T>;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                formatter.write_str("a string containing a PEP 508 requirement")
+            }
+
+            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                FromStr::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(RequirementVisitor(std::marker::PhantomData))
     }
 }
 

crates/uv-pep508/src/marker/tree.rs

@@ -407,8 +407,21 @@ impl<'de> Deserialize<'de> for StringVersion {
     where
         D: Deserializer<'de>,
     {
-        let string = String::deserialize(deserializer)?;
+        struct Visitor;
-        Self::from_str(&string).map_err(de::Error::custom)
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = StringVersion;
+
+            fn expecting(&self, f: &mut Formatter) -> fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                StringVersion::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 
@@ -651,8 +664,21 @@ impl<'de> Deserialize<'de> for MarkerTree {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        FromStr::from_str(&s).map_err(de::Error::custom)
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = MarkerTree;
+
+            fn expecting(&self, f: &mut Formatter) -> fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                MarkerTree::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-pypi-types/src/lenient_requirement.rs

@@ -157,8 +157,21 @@ impl<'de> Deserialize<'de> for LenientVersionSpecifiers {
     where
         D: Deserializer<'de>,
     {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        Self::from_str(&s).map_err(de::Error::custom)
+
+        impl de::Visitor<'_> for Visitor {
+            type Value = LenientVersionSpecifiers;
+
+            fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                LenientVersionSpecifiers::from_str(v).map_err(de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-pypi-types/src/simple_json.rs

@@ -65,13 +65,37 @@ fn deserialize_version_specifiers_lenient<'de, D>(
 where
     D: Deserializer<'de>,
 {
-    let maybe_string: Option<String> = Option::deserialize(deserializer)?;
+    struct Visitor;
-    let Some(string) = maybe_string else {
+
-        return Ok(None);
+    impl<'de> serde::de::Visitor<'de> for Visitor {
-    };
+        type Value = Option<Result<VersionSpecifiers, VersionSpecifiersParseError>>;
-    Ok(Some(
+
-        LenientVersionSpecifiers::from_str(&string).map(VersionSpecifiers::from),
+        fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-    ))
+            f.write_str("a string representing a version specifier")
+        }
+
+        fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+            Ok(Some(
+                LenientVersionSpecifiers::from_str(v).map(VersionSpecifiers::from),
+            ))
+        }
+
+        fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            deserializer.deserialize_str(Visitor)
+        }
+
+        fn visit_none<E>(self) -> Result<Self::Value, E>
+        where
+            E: serde::de::Error,
+        {
+            Ok(None)
+        }
+    }
+
+    deserializer.deserialize_option(Visitor)
 }
 
 #[derive(Debug, Clone)]

crates/uv-python/src/python_version.rs

@@ -63,8 +63,21 @@ impl schemars::JsonSchema for PythonVersion {
 
 impl<'de> serde::Deserialize<'de> for PythonVersion {
     fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
-        let s = String::deserialize(deserializer)?;
+        struct Visitor;
-        PythonVersion::from_str(&s).map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = PythonVersion;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                PythonVersion::from_str(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-resolver/src/lock/mod.rs

@@ -2,7 +2,7 @@ use std::borrow::Cow;
 use std::collections::{BTreeMap, BTreeSet, VecDeque};
 use std::convert::Infallible;
 use std::error::Error;
-use std::fmt::{Debug, Display};
+use std::fmt::{Debug, Display, Formatter};
 use std::io;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
@@ -4361,12 +4361,25 @@ impl Display for Hash {
 }
 
 impl<'de> serde::Deserialize<'de> for Hash {
-    fn deserialize<D>(d: D) -> Result<Hash, D::Error>
+    fn deserialize<D>(deserializer: D) -> Result<Hash, D::Error>
     where
         D: serde::de::Deserializer<'de>,
     {
-        let string = String::deserialize(d)?;
+        struct Visitor;
-        string.parse().map_err(serde::de::Error::custom)
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = Hash;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                Hash::from_str(v).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
     }
 }
 

crates/uv-small-str/src/lib.rs

@@ -85,26 +85,21 @@ impl serde::Serialize for SmallString {
 
 impl<'de> serde::Deserialize<'de> for SmallString {
     fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
-        let s = deserializer.deserialize_str(SmallStringVisitor)?;
+        struct Visitor;
-        Ok(s)
-    }
-}
 
-struct SmallStringVisitor;
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = SmallString;
 
-impl serde::de::Visitor<'_> for SmallStringVisitor {
+            fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-    type Value = SmallString;
+                f.write_str("a string")
+            }
 
-    fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
-        f.write_str("a string")
+                Ok(v.into())
-    }
+            }
+        }
 
-    fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+        deserializer.deserialize_str(Visitor)
-        Ok(v.into())
-    }
-
-    fn visit_string<E: serde::de::Error>(self, v: String) -> Result<Self::Value, E> {
-        Ok(v.into())
     }
 }
 

crates/uv-workspace/src/pyproject.rs

@@ -7,6 +7,7 @@
 //! Then lowers them into a dependency specification.
 
 use std::collections::BTreeMap;
+use std::fmt::Formatter;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
@@ -713,8 +714,39 @@ pub struct ToolUvWorkspace {
 }
 
 /// (De)serialize globs as strings.
-#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
-pub struct SerdePattern(#[serde(with = "serde_from_and_to_string")] pub Pattern);
+pub struct SerdePattern(Pattern);
+
+impl serde::ser::Serialize for SerdePattern {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::ser::Serializer,
+    {
+        self.0.as_str().serialize(serializer)
+    }
+}
+
+impl<'de> serde::Deserialize<'de> for SerdePattern {
+    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+        struct Visitor;
+
+        impl serde::de::Visitor<'_> for Visitor {
+            type Value = SerdePattern;
+
+            fn expecting(&self, f: &mut Formatter) -> std::fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E: serde::de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                Pattern::from_str(v)
+                    .map(SerdePattern)
+                    .map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
+    }
+}
 
 #[cfg(feature = "schemars")]
 impl schemars::JsonSchema for SerdePattern {
@@ -1585,30 +1617,3 @@ pub enum DependencyType {
     /// A dependency in `dependency-groups.{0}`.
     Group(GroupName),
 }
-
-/// <https://github.com/serde-rs/serde/issues/1316#issue-332908452>
-mod serde_from_and_to_string {
-    use std::fmt::Display;
-    use std::str::FromStr;
-
-    use serde::{de, Deserialize, Deserializer, Serializer};
-
-    pub(super) fn serialize<T, S>(value: &T, serializer: S) -> Result<S::Ok, S::Error>
-    where
-        T: Display,
-        S: Serializer,
-    {
-        serializer.collect_str(value)
-    }
-
-    pub(super) fn deserialize<'de, T, D>(deserializer: D) -> Result<T, D::Error>
-    where
-        T: FromStr,
-        T::Err: Display,
-        D: Deserializer<'de>,
-    {
-        String::deserialize(deserializer)?
-            .parse()
-            .map_err(de::Error::custom)
-    }
-}

crates/uv/tests/it/pip_compile.rs

@@ -4131,23 +4131,22 @@ fn override_dependency_from_workspace_invalid_syntax() -> Result<()> {
 
     ----- stderr -----
     warning: Failed to parse `pyproject.toml` during settings discovery:
-      TOML parse error at line 9, column 29
+      TOML parse error at line 10, column 7
-        |
+         |
-      9 |     override-dependencies = [
+      10 |       "werkzeug=2.3.0"
-        |                             ^
+         |       ^^^^^^^^^^^^^^^^
       no such comparison operator "=", must be one of ~= == != <= >= < > ===
       werkzeug=2.3.0
               ^^^^^^
 
     error: Failed to parse: `pyproject.toml`
-      Caused by: TOML parse error at line 9, column 29
+      Caused by: TOML parse error at line 10, column 7
-      |
+       |
-    9 |     override-dependencies = [
+    10 |       "werkzeug=2.3.0"
-      |                             ^
+       |       ^^^^^^^^^^^^^^^^
     no such comparison operator "=", must be one of ~= == != <= >= < > ===
     werkzeug=2.3.0
             ^^^^^^
-
     "###
     );