Fix best-interpreter lookups when there is an invalid interpreter in the PATH

Author: zanieb

crates/uv-python/src/discovery.rs

@@ -1074,10 +1074,16 @@ pub fn find_best_python_installation(
 
     // First, check for an exact match (or the first available version if no Python version was provided)
     debug!("Looking for exact match for request {request}");
-    let result = find_python_installation(request, environments, preference, cache)?;
-    if let Ok(ref installation) = result {
-        warn_on_unsupported_python(installation.interpreter());
-        return Ok(result);
+    let result = find_python_installation(request, environments, preference, cache);
+    match result {
+        Ok(Ok(installation)) => {
+            warn_on_unsupported_python(installation.interpreter());
+            return Ok(Ok(installation));
+        }
+        // Continue if we can't find a matching Python and ignore non-critical discovery errors
+        Ok(Err(_)) => {}
+        Err(ref err) if !err.is_critical() => {}
+        _ => return result,
     }
 
     // If that fails, and a specific patch version was requested try again allowing a
@@ -1096,10 +1102,16 @@ pub fn find_best_python_installation(
         _ => None,
     } {
         debug!("Looking for relaxed patch version {request}");
-        let result = find_python_installation(&request, environments, preference, cache)?;
-        if let Ok(ref installation) = result {
-            warn_on_unsupported_python(installation.interpreter());
-            return Ok(result);
+        let result = find_python_installation(&request, environments, preference, cache);
+        match result {
+            Ok(Ok(installation)) => {
+                warn_on_unsupported_python(installation.interpreter());
+                return Ok(Ok(installation));
+            }
+            // Continue if we can't find a matching Python and ignore non-critical discovery errors
+            Ok(Err(_)) => {}
+            Err(ref err) if !err.is_critical() => {}
+            _ => return result,
         }
     }
 

crates/uv/tests/it/pip_compile.rs

@@ -1412,16 +1412,27 @@ fn compile_fallback_interpreter_broken_in_path() -> Result<()> {
             .arg("3.12")
             // In tests, we ignore `PATH` during Python discovery so we need to add the context `bin`
             .env("UV_TEST_PYTHON_PATH", context.bin_dir.as_os_str()), @r###"
-    success: false
-    exit_code: 2
+    success: true
+    exit_code: 0
     ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] requirements.in --python-version 3.12
+    black==23.10.[X]
+        # via -r requirements.in
+    click==8.1.7
+        # via black
+    mypy-extensions==1.0.0
+        # via black
+    packaging==24.0
+        # via black
+    pathspec==0.12.1
+        # via black
+    platformdirs==4.2.0
+        # via black
 
     ----- stderr -----
-    error: Failed to inspect Python interpreter from search path at `[BIN]/python3`
-      Caused by: Querying Python at `[BIN]/python3` failed with exit status exit status: 1
-
-    [stderr]
-    error: intentionally broken python executable
+    warning: The requested Python version 3.12 is not available; 3.10.[X] will be used to build dependencies instead.
+    Resolved 6 packages in [TIME]
     "###
     );