Use return code instead of stderr to detect errors

Author: jhossbach

pylsp_ruff/plugin.py

@@ -458,7 +458,7 @@ def run_ruff(
         p = Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)
     (stdout, stderr) = p.communicate(document_source.encode())
 
-    if stderr:
+    if p.returncode != 0:
         log.error(f"Error running ruff: {stderr.decode()}")
 
     return stdout.decode()
@@ -491,6 +491,8 @@ def build_arguments(
     args = []
     # Suppress update announcements
     args.append("--quiet")
+    # Suppress exit 1 when violations were found
+    args.append("--exit-zero")
     # Use the json formatting for easier evaluation
     args.append("--output-format=json")
     if fix:

tests/test_ruff_lint.py

@@ -177,6 +177,7 @@ def f():
     assert call_args == [
         "ruff",
         "--quiet",
+        "--exit-zero",
         "--output-format=json",
         "--no-fix",
         "--force-exclude",