Fix IndexError in lit_to_bazel for files without run commands

get_command_without_bazel_prefix crashes with an IndexError when the
input .mlir file has no // RUN: lines (or only FileCheck RUN lines),
because commands[-1] is accessed on an empty list. Guard both the
trailing-pipe pop and the consecutive-pipe dedup against an empty
list so these inputs return an empty command instead of crashing.

Author: rootkiller6788

scripts/lit_to_bazel_lib.py

@@ -130,11 +130,11 @@ def get_command_without_bazel_prefix(lit_test_file) -> str:
   commands = convert_to_run_commands(run_lines)
   commands = [x for x in commands if "FileCheck" not in x]
   # remove consecutive and trailing pipes
-  if commands[-1] == PIPE:
+  if commands and commands[-1] == PIPE:
     commands.pop()
   deduped_commands = []
   for command in commands:
-    if command == PIPE and deduped_commands[-1] == PIPE:
+    if command == PIPE and deduped_commands and deduped_commands[-1] == PIPE:
       continue
     deduped_commands.append(command)
 

scripts/test_lit_to_bazel.py

@@ -8,6 +8,9 @@
 PIPE = lit_to_bazel_lib.PIPE
 convert_to_run_commands = lit_to_bazel_lib.convert_to_run_commands
 normalize_lit_test_file_arg = lit_to_bazel_lib.normalize_lit_test_file_arg
+get_command_without_bazel_prefix = (
+    lit_to_bazel_lib.get_command_without_bazel_prefix
+)
 
 
 class LitToBazelTest(absltest.TestCase):
@@ -186,6 +189,35 @@ def side_effect(path):
             "/workspace/tests/foo.mlir",
         )
 
+  def test_get_command_without_bazel_prefix_no_run_lines(self):
+    """A file with no RUN lines should yield an empty command, not crash."""
+    with absltest.mock.patch(
+        "builtins.open",
+        absltest.mock.mock_open(read_data="func.func @foo() -> i8\n"),
+    ):
+      self.assertEqual(get_command_without_bazel_prefix("fake.mlir"), "")
+
+  def test_get_command_without_bazel_prefix_only_filecheck(self):
+    """A file whose only RUN line is FileCheck should yield an empty command."""
+    with absltest.mock.patch(
+        "builtins.open",
+        absltest.mock.mock_open(read_data="// RUN: FileCheck %s\n"),
+    ):
+      self.assertEqual(get_command_without_bazel_prefix("fake.mlir"), "")
+
+  def test_get_command_without_bazel_prefix_filecheck_then_pipe(self):
+    """A FileCheck command followed by a pipe should not crash."""
+    with absltest.mock.patch(
+        "builtins.open",
+        absltest.mock.mock_open(
+            read_data="// RUN: FileCheck %s | heir-opt --canonicalize\n"
+        ),
+    ):
+      self.assertEqual(
+          get_command_without_bazel_prefix("fake.mlir"),
+          "| heir-opt --canonicalize",
+      )
+
 
 if __name__ == "__main__":
   absltest.main()