Consistently normalize trailing slashes on URLs with no path segments (#14349)

Alternative to https://github.com/astral-sh/uv/pull/14348

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

@@ -171,10 +171,21 @@ impl UrlString {
     }
 
     /// Return the [`UrlString`] (as a [`Cow`]) with trailing slash removed.
+    ///
+    /// This matches the semantics of [`Url::pop_if_empty`], which will not trim a trailing slash if
+    /// it's the only path segment, e.g., `https://example.com/` would be unchanged.
     #[must_use]
     pub fn without_trailing_slash(&self) -> Cow<'_, Self> {
         self.as_ref()
             .strip_suffix('/')
+            .filter(|path| {
+                // Only strip the trailing slash if there's _another_ trailing slash that isn't a
+                // part of the scheme.
+                path.split_once("://")
+                    .map(|(_scheme, rest)| rest)
+                    .unwrap_or(path)
+                    .contains('/')
+            })
             .map(|path| Cow::Owned(UrlString(SmallString::from(path))))
             .unwrap_or(Cow::Borrowed(self))
     }
@@ -283,5 +294,20 @@ mod tests {
             url.without_trailing_slash(),
             Cow::Owned(UrlString("https://example.com/path".into()))
         );
+
+        // Does not remove a trailing slash if it's the only path segment
+        let url = UrlString("https://example.com/".into());
+        assert_eq!(url.without_trailing_slash(), Cow::Borrowed(&url));
+
+        // Does not remove a trailing slash if it's the only path segment with a missing scheme
+        let url = UrlString("example.com/".into());
+        assert_eq!(url.without_trailing_slash(), Cow::Borrowed(&url));
+
+        // Removes the trailing slash when the scheme is missing
+        let url = UrlString("example.com/path/".into());
+        assert_eq!(
+            url.without_trailing_slash(),
+            Cow::Owned(UrlString("example.com/path".into()))
+        );
     }
 }