Handle shape mismatch for cirq.dirac_notation (#6179)

Throwing a value error when there is a shape mismatch between state_vector and qid_shape. It also throws an error when qid_shape is not mentioned and length of state_vector is not a power of 2.

Fixes #6165

cirq-core/cirq/qis/states.py

@@ -714,10 +714,22 @@ def dirac_notation(
     Returns:
         A pretty string consisting of a sum of computational basis kets
         and non-zero floats of the specified accuracy.
+
+    Raises:
+        ValueError: If there is a shape mismatch between state_vector and qid_shape.
+            Otherwise, when qid_shape is not mentioned and length of state_vector
+            is not a power of 2.
     """
     if qid_shape is None:
         qid_shape = (2,) * (len(state_vector).bit_length() - 1)
 
+    if len(state_vector) != np.prod(qid_shape, dtype=np.int64):
+        raise ValueError(
+            'state_vector has incorrect size. Expected {} but was {}.'.format(
+                np.prod(qid_shape, dtype=np.int64), len(state_vector)
+            )
+        )
+
     digit_separator = '' if max(qid_shape, default=0) < 10 else ','
     perm_list = [
         digit_separator.join(seq)
@@ -821,7 +833,6 @@ def to_valid_state_vector(
 def _qudit_values_to_state_tensor(
     *, state_vector: np.ndarray, qid_shape: Tuple[int, ...], dtype: Optional['DTypeLike']
 ) -> np.ndarray:
-
     for i in range(len(qid_shape)):
         s = state_vector[i]
         q = qid_shape[i]

cirq-core/cirq/qis/states_test.py

@@ -475,6 +475,13 @@ def test_dirac_notation_precision():
     assert_dirac_notation_python([sqrt, sqrt], "0.707|0⟩ + 0.707|1⟩", decimals=3)
 
 
+def test_dirac_notation_invalid():
+    with pytest.raises(ValueError, match='state_vector has incorrect size'):
+        _ = cirq.dirac_notation([0.0, 0.0, 1.0])
+    with pytest.raises(ValueError, match='state_vector has incorrect size'):
+        _ = cirq.dirac_notation([1.0, 1.0], qid_shape=(3,))
+
+
 def test_to_valid_state_vector():
     with pytest.raises(ValueError, match='Computational basis state is out of range'):
         cirq.to_valid_state_vector(2, 1)