t.list: Check connection to prevent creating temporal database

temporal/t.list/t.list.py

@@ -99,6 +99,7 @@
 from contextlib import nullcontext
 
 import grass.script as gs
+from grass.tools import Tools
 
 ############################################################################
 
@@ -149,6 +150,27 @@ def main():
     elif not separator:  # output_format == "plain"
         separator = "|"
 
+    tools = Tools()
+
+    conn = tools.t_connect(flags="p", format="json")
+
+    db_exists = conn["driver"] and conn["database"]
+
+    # if no connection is found
+    if not db_exists:
+        if output_format == "plain":
+            gs.message(
+                _("No temporal database exists in this mapset. No datasets to list.")
+            )
+        with (
+            open(outpath, "w")
+            if (outpath and outpath != "-")
+            else nullcontext(sys.stdout)
+        ) as out_file:
+            if output_format == "json":
+                out_file.write(json.dumps([], indent=4) + "\n")
+        return
+
     # Lazy import
     import grass.temporal as tgis
 

temporal/t.list/tests/conftest.py

@@ -56,3 +56,14 @@ def space_time_dataset(tmp_path_factory):
             name=dataset_name,
             map_names=names,
         )
+
+
+@pytest.fixture(scope="module")
+def empty_session(tmp_path_factory):
+    """Start an isolated session with no temporal database."""
+    tmp_path = tmp_path_factory.mktemp("empty_time_series")
+    project = tmp_path / "empty_project"
+    gs.create_project(project)
+
+    with gs.setup.init(project, env=os.environ.copy()) as session:
+        yield SimpleNamespace(session=session)

temporal/t.list/tests/test_t_list.py

@@ -131,3 +131,23 @@ def test_colhead_validation(space_time_dataset, output_format):
         assert status == 0
     else:
         assert status != 0
+
+
+def test_t_list_empty_database(empty_session):
+    """Verify that t.list handles a missing TGIS database without creating one."""
+    tools = Tools(session=empty_session.session)
+
+    json_result = tools.t_list(type="strds", format="json")
+    assert json_result.returncode == 0
+    assert json_result.stdout.strip() == "[]"
+
+    csv_result = tools.t_list(type="strds", format="csv")
+    assert csv_result is None
+
+    plain_result = tools.t_list(type="strds", format="plain")
+    assert plain_result is None
+
+    # Ensure no connection is established
+    result = tools.t_connect(flags="p", format="json")
+    db_exist = result["driver"] and result["database"]
+    assert not db_exist