fall back to system ruff executable without executable setting

pylsp_ruff/plugin.py

@@ -1,8 +1,11 @@
 import enum
+import importlib.util
 import json
 import logging
 import re
+import shutil
 import sys
+from functools import lru_cache
 from pathlib import PurePath
 from subprocess import PIPE, Popen
 from typing import Dict, Generator, List, Optional
@@ -116,7 +119,6 @@ def pylsp_format_document(workspace: Workspace, document: Document) -> Generator
         Document to apply ruff on.
 
     """
-
     log.debug(f"textDocument/formatting: {document}")
     outcome = yield
     result = outcome.get_result()
@@ -178,7 +180,6 @@ def pylsp_lint(workspace: Workspace, document: Document) -> List[Dict]:
     List of dicts containing the diagnostics.
 
     """
-
     with workspace.report_progress("lint: ruff"):
         settings = load_settings(workspace, document.path)
         checks = run_ruff_check(document=document, settings=settings)
@@ -487,6 +488,37 @@ def run_ruff_format(
     )
 
 
+@lru_cache
+def find_executable(executable) -> List[str]:
+    cmd = None
+    # use the explicit executable configuration
+    if executable is not None:
+        exe_path = shutil.which(executable)
+        if exe_path is not None:
+            cmd = [exe_path]
+        else:
+            log.error(f"Configured ruff executable not found: {executable!r}")
+
+    # try the python module
+    if cmd is None:
+        if importlib.util.find_spec("ruff") is not None:
+            cmd = [sys.executable, "-m", "ruff"]
+
+    # try system's ruff executable
+    if cmd is None:
+        system_exe = shutil.which("ruff")
+        if system_exe is not None:
+            cmd = [system_exe]
+
+    if cmd is None:
+        log.error(
+            "No suitable ruff invocation could be found (executable, python module)."
+        )
+        cmd = []
+
+    return cmd
+
+
 def run_ruff(
     settings: PluginSettings,
     document_path: str,
@@ -522,27 +554,14 @@ def run_ruff(
 
     arguments = subcommand.build_args(document_path, settings, fix, extra_arguments)
 
-    p = None
-    if executable is not None:
-        log.debug(f"Calling {executable} with args: {arguments} on '{document_path}'")
-        try:
-            cmd = [executable, str(subcommand)]
-            cmd.extend(arguments)
-            p = Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)
-        except Exception:
-            log.error(f"Can't execute ruff with given executable '{executable}'.")
-    if p is None:
-        log.debug(
-            f"Calling ruff via '{sys.executable} -m ruff'"
-            f" with args: {arguments} on '{document_path}'"
-        )
-        cmd = [sys.executable, "-m", "ruff", str(subcommand)]
-        cmd.extend(arguments)
-        p = Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)
-    (stdout, stderr) = p.communicate(document_source.encode())
+    cmd = [*find_executable(executable), str(subcommand), *arguments]
+
+    log.debug(f"Calling {cmd} on '{document_path}'")
+    p = Popen(cmd, stdin=PIPE, stdout=PIPE)
+    (stdout, _) = p.communicate(document_source.encode())
 
     if p.returncode != 0:
-        log.error(f"Error running ruff: {stderr.decode()}")
+        log.error(f"Ruff returned {p.returncode} != 0")
 
     return stdout.decode()
 

tests/test_ruff_lint.py

@@ -2,6 +2,7 @@
 # Copyright 2021- Python Language Server Contributors.
 
 import os
+import stat
 import sys
 import tempfile
 from unittest.mock import Mock, patch
@@ -100,17 +101,24 @@ def test_ruff_config_param(workspace):
 
 def test_ruff_executable_param(workspace):
     with patch("pylsp_ruff.plugin.Popen") as popen_mock:
-        mock_instance = popen_mock.return_value
-        mock_instance.communicate.return_value = [bytes(), bytes()]
+        with tempfile.NamedTemporaryFile() as ruff_exe:
+            mock_instance = popen_mock.return_value
+            mock_instance.communicate.return_value = [bytes(), bytes()]
 
-        ruff_executable = "/tmp/ruff"
-        workspace._config.update({"plugins": {"ruff": {"executable": ruff_executable}}})
+            ruff_executable = ruff_exe.name
+            # chmod +x the file
+            st = os.stat(ruff_executable)
+            os.chmod(ruff_executable, st.st_mode | stat.S_IEXEC)
 
-        _name, doc = temp_document(DOC, workspace)
-        ruff_lint.pylsp_lint(workspace, doc)
+            workspace._config.update(
+                {"plugins": {"ruff": {"executable": ruff_executable}}}
+            )
 
-        (call_args,) = popen_mock.call_args[0]
-        assert ruff_executable in call_args
+            _name, doc = temp_document(DOC, workspace)
+            ruff_lint.pylsp_lint(workspace, doc)
+
+            (call_args,) = popen_mock.call_args[0]
+            assert ruff_executable in call_args
 
 
 def get_ruff_settings(workspace, doc, config_str):