cat-log list-dir mode: fail gracefully

changes.d/6511.fix.md

@@ -0,0 +1 @@
+cat-log command list-dir mode: fail gracefully if directory not found.

cylc/flow/scripts/cat_log.py

@@ -261,13 +261,17 @@ def view_log(
         print(os.path.dirname(logpath))
         return 0
     if mode == 'list-dir':
-        for entry in sorted(os.listdir(os.path.dirname(logpath))):
+        dirname = os.path.dirname(logpath)
+        if not os.path.exists(dirname):
+            sys.stderr.write(f"Directory not found: {dirname}\n")
+            return 1
+        for entry in sorted(os.listdir(dirname)):
             print(entry)
         return 0
     if not os.path.exists(logpath) and batchview_cmd is None:
         # Note: batchview_cmd may not need to have access to logpath, so don't
         # test for existence of path if it is set.
-        sys.stderr.write('file not found: %s\n' % logpath)
+        sys.stderr.write('File not found: %s\n' % logpath)
         return 1
     if prepend_path:
         from cylc.flow.hostuserutil import get_host

tests/integration/scripts/test_cat_log.py

@@ -92,6 +92,22 @@ def test_bad_workflow2(run_dir, brokendir, capsys):
             BAD_NAME
         )
     msg = (
-        f'file not found: {run_dir}'
+        f'File not found: {run_dir}'
         '/NONEXISTENTWORKFLOWNAME/log/j\n')
     assert capsys.readouterr().err == msg
+
+
+def test_bad_task_dir(run_dir, brokendir, capsys):
+    """Check a non existent job log dir in a valid workflow results in error.
+    """
+    parser = cat_log_gop()
+    with pytest.raises(SystemExit, match='1'):
+        cat_log(
+            parser,
+            Options(parser)(mode='list-dir'),
+            BAD_NAME + "//1/foo"
+        )
+    msg = (
+        f'Directory not found: {run_dir}'
+        '/NONEXISTENTWORKFLOWNAME/log/job/1/foo/NN\n')
+    assert capsys.readouterr().err == msg