normalize reported rows in BlockIndex, updated caching

Author: flexatone

src/_arraykit.c

@@ -5304,6 +5304,7 @@ BlockIndex_register(BlockIndexObject *self, PyObject *value) {
     Py_ssize_t alignment = PyArray_DIM(a, 0);
     if (self->row_count == -1) {
         self->row_count = alignment;
+        self->shape_recache = true; // setting rows, must recache shape
     }
     else if (self->row_count != alignment) {
         PyErr_Format(ErrorInitTypeBlocks,
@@ -5422,12 +5423,17 @@ BlockIndex_setstate(BlockIndexObject *self, PyObject *state)
 //------------------------------------------------------------------------------
 // getters
 
+// Never expose a negative row value to the caller
+#define AK_BI_ROWS(rows) ((rows) < 0 ? 0 : (rows))
+
 static PyObject *
 BlockIndex_shape_getter(BlockIndexObject *self, void* Py_UNUSED(closure))
 {
     if (self->shape == NULL || self->shape_recache) {
         Py_XDECREF(self->shape); // get rid of old if it exists
-        self->shape = AK_build_pair_ssize_t(self->row_count, self->bir_count);
+        self->shape = AK_build_pair_ssize_t(
+                AK_BI_ROWS(self->row_count),
+                self->bir_count);
     }
     // shape is not null and shape_recache is false
     Py_INCREF(self->shape); // for caller
@@ -5437,7 +5443,7 @@ BlockIndex_shape_getter(BlockIndexObject *self, void* Py_UNUSED(closure))
 
 static PyObject *
 BlockIndex_rows_getter(BlockIndexObject *self, void* Py_UNUSED(closure)){
-    return PyLong_FromSsize_t(self->row_count);
+    return PyLong_FromSsize_t(AK_BI_ROWS(self->row_count));
 }
 
 static PyObject *

test/test_block_index.py

@@ -16,9 +16,9 @@ def test_block_index_init_a(self) -> None:
         bi1 = BlockIndex()
         self.assertEqual(bi1.dtype, np.dtype(float))
         s = bi1.shape
-        self.assertEqual(s, (-1, 0))
+        self.assertEqual(s, (0, 0))
         del bi1
-        self.assertEqual(s, (-1, 0))
+        self.assertEqual(s, (0, 0))
         del s
 
     def test_block_index_init_b1(self) -> None:
@@ -850,3 +850,17 @@ def test_block_index_iter_block_c(self) -> None:
 
         slc = slice(None)
         self.assertEqual(list(bi1.iter_block()), [(i, slc) for i in range(8)])
+
+    #---------------------------------------------------------------------------
+
+    def test_block_index_shape_a(self) -> None:
+        bi1 = BlockIndex()
+        self.assertEqual(bi1.shape, (0, 0))
+        self.assertEqual(bi1.rows, 0)
+
+        bi1.register(np.array(()).reshape(2,0))
+        self.assertEqual(bi1.shape, (2, 0))
+        self.assertEqual(bi1.rows, 2)
+
+        with self.assertRaises(ErrorInitTypeBlocks):
+            bi1.register(np.array(()).reshape(3,0))