BUG: Ensure correct behavior for rows ending in delimiter in loadtxt (#22836)

If a row ends in a delimiter, `add_fields` can be called twice without
any field actually being parsed.  This causes issues with the field
buffer setup.

closes gh-22833

1 files changed, 12 insertions, 0 deletions

diff --git a/numpy/lib/tests/test_loadtxt.py b/numpy/lib/tests/test_loadtxt.py
index 0b8fe3c47..819a8dda4 100644
--- a/numpy/lib/tests/test_loadtxt.py
+++ b/numpy/lib/tests/test_loadtxt.py
@@ -1011,3 +1011,15 @@ def test_control_characters_as_bytes():
     """Byte control characters (comments, delimiter) are supported."""
     a = np.loadtxt(StringIO("#header\n1,2,3"), comments=b"#", delimiter=b",")
     assert_equal(a, [1, 2, 3])
+
+
+@pytest.mark.filterwarnings('ignore::UserWarning')
+def test_field_growing_cases():
+    # Test empty field appending/growing (each field still takes 1 character)
+    # to see if the final field appending does not create issues.
+    res = np.loadtxt([""], delimiter=",", dtype=bytes)
+    assert len(res) == 0
+
+    for i in range(1, 1024):
+        res = np.loadtxt(["," * i], delimiter=",", dtype=bytes)
+        assert len(res) == i+1