Fix serialization of index URLs (#3289)

Closes https://github.com/astral-sh/uv/issues/3288.

crates/distribution-types/src/index_url.rs

@@ -20,7 +20,7 @@ static DEFAULT_INDEX_URL: Lazy<IndexUrl> =
     Lazy::new(|| IndexUrl::Pypi(VerbatimUrl::from_url(PYPI_URL.clone())));
 
 /// The url of an index, newtype'd to avoid mixing it with file urls.
-#[derive(Debug, Clone, Hash, Eq, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Hash, Eq, PartialEq)]
 pub enum IndexUrl {
     Pypi(VerbatimUrl),
     Url(VerbatimUrl),
@@ -100,6 +100,25 @@ impl FromStr for IndexUrl {
     }
 }
 
+impl serde::ser::Serialize for IndexUrl {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::ser::Serializer,
+    {
+        self.verbatim().serialize(serializer)
+    }
+}
+
+impl<'de> serde::de::Deserialize<'de> for IndexUrl {
+    fn deserialize<D>(deserializer: D) -> Result<IndexUrl, D::Error>
+    where
+        D: serde::de::Deserializer<'de>,
+    {
+        let s = String::deserialize(deserializer)?;
+        IndexUrl::from_str(&s).map_err(serde::de::Error::custom)
+    }
+}
+
 impl From<VerbatimUrl> for IndexUrl {
     fn from(url: VerbatimUrl) -> Self {
         if *url.raw() == *PYPI_URL {

crates/uv/tests/pip_compile.rs

@@ -8217,6 +8217,7 @@ fn resolve_configuration() -> Result<()> {
         [pip]
         resolution = "lowest-direct"
         generate-hashes = true
+        index-url = "https://pypi.org/simple"
     "#})?;
 
     let requirements_in = context.temp_dir.child("requirements.in");
@@ -8358,6 +8359,7 @@ fn resolve_configuration() -> Result<()> {
         [tool.uv.pip]
         resolution = "lowest-direct"
         generate-hashes = true
+        index-url = "https://pypi.org/simple"
     "#})?;
 
     // Resolution should use the lowest direct version, and generate hashes.