restore the prior @latest error message

Author: oconnor663

crates/uv-python/src/discovery.rs

@@ -238,6 +238,10 @@ pub enum Error {
     #[error("Invalid version request: {0}")]
     InvalidVersionRequest(String),
 
+    /// An invalid version request was given
+    #[error("Requesting the 'latest' Python version is not yet supported")]
+    LatestVersionRequest,
+
     // TODO(zanieb): Is this error case necessary still? We should probably drop it.
     #[error("Interpreter discovery for `{0}` requires `{1}` but only `{2}` is allowed")]
     SourceNotAllowed(PythonRequest, PythonSource, PythonPreference),
@@ -1578,6 +1582,11 @@ impl PythonRequest {
         // The @ separator is optional. If it's present, the right half must be a version, and
         // parsing errors are raised to the caller.
         if let Some(after_at) = rest.strip_prefix('@') {
+            if after_at == "latest" {
+                // Handle `@latest` as a special case. It's still an error for now, but we plan to
+                // support it. TODO(zanieb): Add `PythonRequest::Latest`
+                return Err(Error::LatestVersionRequest);
+            }
             return after_at.parse().map(Some);
         }
         // The @ was not present, so if the version fails to parse just return Ok(None). For

crates/uv/tests/it/tool_run.rs

@@ -2039,14 +2039,14 @@ fn tool_run_python_at_version() {
     // Request `@latest` (not yet supported)
     uv_snapshot!(context.filters(), context.tool_run()
         .arg("python@latest")
-        .arg("--version"), @r"
+        .arg("--version"), @r###"
     success: false
     exit_code: 2
     ----- stdout -----
 
     ----- stderr -----
-    error: Invalid version request: latest
-    ");
+    error: Requesting the 'latest' Python version is not yet supported
+    "###);
 }
 
 #[test]