Show non-critical Python discovery errors if no other interpreter is …

…found

We show the first one, sort of arbitrarily but I think it matches user expectation

crates/uv-python/src/discovery.rs

@@ -971,9 +971,14 @@ pub(crate) fn find_python_installation(
 ) -> Result<FindPythonResult, Error> {
     let installations = find_python_installations(request, environments, preference, cache);
     let mut first_prerelease = None;
+    let mut first_error = None;
     for result in installations {
         // Iterate until the first critical error or happy result
         if !result.as_ref().err().map_or(true, Error::is_critical) {
+            // Track the first non-critical error
+            if first_error.is_none() {
+                first_error = Some(result);
+            }
             continue;
         }
 
@@ -1026,6 +1031,12 @@ pub(crate) fn find_python_installation(
         return Ok(Ok(installation));
     }
 
+    // If we found a Python, but it was unusable for some reason, report that instead of saying we
+    // couldn't find any Python interpreters.
+    if let Some(result) = first_error {
+        return result;
+    }
+
     Ok(Err(PythonNotFound {
         request: request.clone(),
         environment_preference: environments,

crates/uv-python/src/lib.rs

@@ -111,7 +111,7 @@ mod tests {
 
     use crate::{
         discovery::{
-            find_best_python_installation, find_python_installation, EnvironmentPreference,
+            self, find_best_python_installation, find_python_installation, EnvironmentPreference,
         },
         PythonPreference,
     };
@@ -589,11 +589,10 @@ mod tests {
                 PythonPreference::default(),
                 &context.cache,
             )
-        })?;
+        });
         assert!(
-            matches!(result, Err(PythonNotFound { .. })),
-            // TODO(zanieb): We could improve the error handling to hint this to the user
-            "If only Python 2 is available, we should not find a python; got {result:?}"
+            matches!(result, Err(discovery::Error::Query(..))),
+            "If only Python 2 is available, we should report the interpreter query error; got {result:?}"
         );
 
         Ok(())

crates/uv/tests/it/python_find.rs

@@ -28,7 +28,8 @@ fn python_find() {
         ----- stdout -----
 
         ----- stderr -----
-        error: No interpreter found in virtual environments, managed installations, or search path
+        error: Failed to inspect Python interpreter from active virtual environment at `.venv/bin/python3`
+          Caused by: Python interpreter not found at `[VENV]/bin/python3`
         "###);
     }
 
@@ -124,7 +125,8 @@ fn python_find() {
         ----- stdout -----
 
         ----- stderr -----
-        error: No interpreter found for PyPy in virtual environments, managed installations, or search path
+        error: Failed to inspect Python interpreter from active virtual environment at `.venv/bin/python3`
+          Caused by: Python interpreter not found at `[VENV]/bin/python3`
         "###);
     }
 
@@ -536,7 +538,8 @@ fn python_find_unsupported_version() {
     ----- stdout -----
 
     ----- stderr -----
-    error: No interpreter found for Python 4.2 in virtual environments, managed installations, or search path
+    error: Failed to inspect Python interpreter from active virtual environment at `.venv/bin/python3`
+      Caused by: Python interpreter not found at `[VENV]/bin/python3`
     "###);
 
     // Request a low version with a range
@@ -546,7 +549,8 @@ fn python_find_unsupported_version() {
     ----- stdout -----
 
     ----- stderr -----
-    error: No interpreter found for Python <3.0 in virtual environments, managed installations, or search path
+    error: Failed to inspect Python interpreter from active virtual environment at `.venv/bin/python3`
+      Caused by: Python interpreter not found at `[VENV]/bin/python3`
     "###);
 
     // Request free-threaded Python on unsupported version