Ensure only files are passed to ktlint for autofixing

Avoids passing random log output from the ktlint check run to the second
autofix pass of ktlint. Unfortunately, this requires disabling log
output for the check run as ktlint puts logging onto stdout, for
whatever reason.

Fixes: #162

language_formatters_pre_commit_hooks/pretty_format_kotlin.py

@@ -1,5 +1,7 @@
 # -*- coding: utf-8 -*-
 import argparse
+import json
+import subprocess  # nosec B404
 import sys
 import typing
 
@@ -65,13 +67,28 @@ def pretty_format_kotlin(argv: typing.Optional[typing.List[str]] = None) -> int:
     # To workaround this limitation we do run ktlint in check mode only,
     # which provides the expected exit status and we run it again in format
     # mode if autofix flag is enabled
-    check_status, check_output = run_command(
-        "java", *jvm_args, "-jar", ktlint_jar, "--log-level", "debug", "--relative", "--", *_fix_paths(args.filenames)
+    #
+    # Logging must be suppressed here as it goes to stdout. This would
+    # interfere with parsing the output JSON.
+    check_result = subprocess.run(  # nosec: B603 B607
+        [
+            "java",
+            *jvm_args,
+            "-jar",
+            ktlint_jar,
+            "--log-level",
+            "none",
+            "--reporter=json",
+            "--relative",
+            "--",
+            *_fix_paths(args.filenames),
+        ],
+        capture_output=True,
     )
 
     not_pretty_formatted_files: typing.Set[str] = set()
-    if check_status != 0:
-        not_pretty_formatted_files.update(line.split(":", 1)[0] for line in check_output.splitlines())
+    if check_result.returncode != 0:
+        not_pretty_formatted_files.update(item["file"] for item in json.loads(check_result.stdout))
 
         if args.autofix:
             print("Running ktlint format on {}".format(not_pretty_formatted_files))