[bug] MatrixType bug fix: Add additional restrictions for unpacking a…

… Matrix (#6795)

Issue: #5819

### Brief Summary

python/taichi/lang/ast/ast_transformer.py

@@ -153,6 +153,10 @@ def build_assign_unpack(ctx, node_target, values, is_static_assign):
 
         # Unpack: a, b, c = ti.Vector([1., 2., 3.])
         if isinstance(values, impl.Expr) and values.ptr.is_tensor():
+            if len(values.get_shape()) > 1:
+                raise ValueError(
+                    'Matrices with more than one columns cannot be unpacked')
+
             values = ctx.ast_builder.expand_expr([values.ptr])
             if len(values) == 1:
                 values = values[0]

tests/python/test_tuple_assign.py

@@ -207,8 +207,7 @@ def func():
         func()
 
 
-@test_utils.test(arch=get_host_arch_list())
-def test_unpack_mismatch_matrix():
+def _test_unpack_mismatch_matrix():
     a = ti.field(ti.f32, ())
     b = ti.field(ti.f32, ())
     c = ti.field(ti.f32, ())
@@ -223,6 +222,18 @@ def func():
         func()
 
 
+@test_utils.test(arch=get_host_arch_list())
+def test_unpack_mismatch_matrix():
+    _test_unpack_mismatch_matrix()
+
+
+@test_utils.test(arch=get_host_arch_list(),
+                 real_matrix=True,
+                 real_matrix_scalarize=True)
+def test_unpack_mismatch_matrix_scalarize():
+    _test_unpack_mismatch_matrix()
+
+
 @test_utils.test(arch=get_host_arch_list())
 def test_unpack_from_shape():
     a = ti.field(ti.f32, ())