Implement timeout hang test

Author: ayylol

llvm/utils/lit/tests/Inputs/timeout-hang/lit.cfg

@@ -1,7 +1,7 @@
 import lit.formats
 
 config.name = "timeout-hang"
-config.suffixes = [".py"]
+config.suffixes = [".txt"]
 config.test_format = lit.formats.ShTest()
 config.test_source_root = None
 config.test_exec_root = None

llvm/utils/lit/tests/Inputs/timeout-hang/run-nonexistent.py renamed to llvm/utils/lit/tests/Inputs/timeout-hang/run-nonexistent.txt

@@ -1,6 +1,27 @@
 # REQUIRES: lit-max-individual-test-time
 
-# https://github.com/llvm/llvm-project/issues/133914
+# Python has some issues dealing with exceptions when multiprocessing,
+# which can cause hangs. Previously this could occur when we encountered
+# an internal shell exception, and had a timeout set.
 
-# RUN: not %{lit} %{inputs}/timeout-hang/run-nonexistent.py \
-# RUN: --timeout=1 --param external=0 -a
+# This test runs a lit test that tries to launch a non-existent file,
+# throwing an exception. We expect this to fail immediately, rather than
+# timeout.
+
+# DEFINE: %{timeout}=1
+
+# RUN: not %{lit} %{inputs}/timeout-hang/run-nonexistent.txt \
+# RUN: --timeout=%{timeout} --param external=0 | %{python} %s %{timeout}
+
+import sys
+import re
+
+timeout_time = float(sys.argv[1])
+testing_time = float(re.search(r'Testing Time: (.*)s', sys.stdin.read()).group(1))
+
+if testing_time < timeout_time:
+    print("Testing took less than timeout")
+    sys.exit(0)
+else:
+    print("Testing took as long or longer than timeout")
+    sys.exit(1)