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

crates/uv-python/src/discovery.rs

@@ -977,9 +977,16 @@ 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() {
+                if let Err(err) = result {
+                    first_error = Some(err);
+                }
+            }
             continue;
         }
 
@@ -1032,6 +1039,12 @@ 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(err) = first_error {
+        return Err(err);
+    }
+
     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/common/mod.rs

@@ -636,7 +636,7 @@ impl TestContext {
             .env(EnvVars::UV_PREVIEW, "1")
             .env(EnvVars::UV_PYTHON_INSTALL_DIR, "")
             .current_dir(&self.temp_dir);
-        self.add_shared_args(&mut command, true);
+        self.add_shared_args(&mut command, false);
         command
     }
 

crates/uv/tests/it/pip_sync.rs

@@ -51,7 +51,10 @@ fn missing_requirements_txt() {
 
 #[test]
 fn missing_venv() -> Result<()> {
-    let context = TestContext::new("3.12");
+    let context = TestContext::new("3.12")
+        .with_filtered_virtualenv_bin()
+        .with_filtered_python_names();
+
     let requirements = context.temp_dir.child("requirements.txt");
     requirements.write_str("anyio")?;
     fs::remove_dir_all(&context.venv)?;
@@ -61,6 +64,19 @@ fn missing_venv() -> Result<()> {
     exit_code: 2
     ----- stdout -----
 
+    ----- stderr -----
+    error: Failed to inspect Python interpreter from active virtual environment at `.venv/[BIN]/python`
+      Caused by: Python interpreter not found at `[VENV]/[BIN]/python`
+    "###);
+
+    assert!(predicates::path::missing().eval(&context.venv));
+
+    // If not "active", we hint to create one
+    uv_snapshot!(context.filters(), context.pip_sync().arg("requirements.txt").env_remove("VIRTUAL_ENV"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
     ----- stderr -----
     error: No virtual environment found; run `uv venv` to create an environment, or pass `--system` to install into a non-virtual environment
     "###);

crates/uv/tests/it/python_find.rs

@@ -569,7 +569,7 @@ fn python_find_venv_invalid() {
         .with_filtered_virtualenv_bin();
 
     // We find the virtual environment
-    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    uv_snapshot!(context.filters(), context.python_find().env(EnvVars::VIRTUAL_ENV, context.venv.as_os_str()), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -581,7 +581,7 @@ fn python_find_venv_invalid() {
     // If the binaries are missing from a virtual environment, we fail
     fs_err::remove_dir_all(venv_bin_path(&context.venv)).unwrap();
 
-    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    uv_snapshot!(context.filters(), context.python_find().env(EnvVars::VIRTUAL_ENV, context.venv.as_os_str()), @r###"
     success: false
     exit_code: 2
     ----- stdout -----
@@ -592,7 +592,7 @@ fn python_find_venv_invalid() {
     "###);
 
     // Unless the virtual environment is not active
-    uv_snapshot!(context.filters(), context.python_find().env_remove(EnvVars::VIRTUAL_ENV), @r###"
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -604,7 +604,7 @@ fn python_find_venv_invalid() {
     // If there's not a `pyvenv.cfg` file, it's also non-fatal, we ignore the environment
     fs_err::remove_file(context.venv.join("pyvenv.cfg")).unwrap();
 
-    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    uv_snapshot!(context.filters(), context.python_find().env(EnvVars::VIRTUAL_ENV, context.venv.as_os_str()), @r###"
     success: true
     exit_code: 0
     ----- stdout -----