Disallow run n and run x as flow names

CHANGES.md

@@ -56,6 +56,9 @@ First Release Candidate for Cylc 8.
 
 ### Enhancements
 
+[#4526](https://github.com/cylc/cylc-flow/pull/4526) - Prevent runN and run\d+
+being allowed as installation target names.
+
 [#4442](https://github.com/cylc/cylc-flow/pull/4442) - Prevent installation
 of workflows inside other installed workflows.
 

cylc/flow/workflow_files.py

@@ -1311,7 +1311,7 @@ def _parse_src_reg(reg: Path, cur_dir_only: bool = False) -> Tuple[Path, Path]:
     return (reg, abs_path)
 
 
-def validate_workflow_name(name: str) -> None:
+def validate_workflow_name(name: str, runNcheck=False) -> None:
     """Check workflow name is valid and not an absolute path.
 
     Raise WorkflowFilesError if not valid.
@@ -1331,6 +1331,11 @@ def validate_workflow_name(name: str) -> None:
             "Workflow name cannot be a path that points to the cylc-run "
             "directory or above"
         )
+    if runNcheck and re.findall(r'^run(N|\d+)$', Path(name).name):
+        raise WorkflowFilesError(
+            "Workflow name cannot be a folder called 'runN' or "
+            "'run<number>'."
+        )
 
 
 def infer_latest_run(
@@ -1626,7 +1631,7 @@ def install_workflow(
     source = Path(expand_path(source))
     if not workflow_name:
         workflow_name = source.name
-    validate_workflow_name(workflow_name)
+    validate_workflow_name(workflow_name, runNcheck=True)
     if run_name in WorkflowFiles.RESERVED_NAMES:
         raise WorkflowFilesError(f'Run name cannot be "{run_name}".')
     if run_name is not None and len(Path(run_name).parts) != 1:

tests/unit/test_workflow_files.py

@@ -181,12 +181,17 @@ def test_check_nested_dirs_install_dirs(
      ('$HOME/alone', WorkflowFilesError, "invalid workflow name"),
      ('./foo', WorkflowFilesError, "invalid workflow name"),
      ('meow/..', WorkflowFilesError,
-      "cannot be a path that points to the cylc-run directory or above")]
+      "cannot be a path that points to the cylc-run directory or above"),
+     ('run6', WorkflowFilesError, "cannot be a folder called 'runN'"),
+     ('e/run6', WorkflowFilesError, "cannot be a folder called 'runN'"),
+     ('runN', WorkflowFilesError, "cannot be a folder called 'runN'"),
+     ('e/runN', WorkflowFilesError, "cannot be a folder called 'runN'")]
 )
 def test_validate_workflow_name(reg, expected_err, expected_msg):
     if expected_err:
         with pytest.raises(expected_err) as exc:
-            workflow_files.validate_workflow_name(reg)
+            runNcheck = 'cannot be a folder called' in expected_msg
+            workflow_files.validate_workflow_name(reg, runNcheck=runNcheck)
         if expected_msg:
             assert expected_msg in str(exc.value)
     else:
@@ -1628,6 +1633,7 @@ def mocked_remote_clean_cmd_side_effect(reg, platform, rm_dirs, timeout):
         for p_name in failed_platforms:
             assert f"{p_name} - {PlatformError.MSG_TIDY}" in caplog.text
 
+
 @pytest.mark.parametrize(
     'rm_dirs, expected_args',
     [
@@ -1809,6 +1815,7 @@ def test_check_flow_file(
     else:
         assert check_flow_file(tmp_path) == tmp_path.joinpath(expected_file)
 
+
 def test_detect_both_flow_and_suite(tmp_path):
     """Test flow.cylc and suite.rc together in dir raises error."""
     tmp_path.joinpath(WorkflowFiles.FLOW_FILE).touch()
@@ -1824,6 +1831,7 @@ def test_detect_both_flow_and_suite(tmp_path):
             "#backward-compatibility"
         )
 
+
 @pytest.mark.parametrize(
     'flow_file_target, suiterc_exists, err, expected_file',
     [