explicit error for unbound Variable in program (#16971)

also allow Tensor(UOp, dtype)

test/backend/test_tensor_variable.py

@@ -28,16 +28,16 @@ class TestTensorVariable(unittest.TestCase):
 
   def test_variable_tensor_dtype_arg(self):
     vv = Variable("a", 1, 10).bind(2)
-    # TODO: dtype arg is silently dropped for a symbolic int, should be honored (or rejected)
-    try:
-      self.assertEqual(Tensor(vv, dtype=dtypes.float32).dtype, dtypes.float32)
-    except AssertionError: pass
+    t = Tensor(vv, dtype=dtypes.float32)
+    self.assertEqual(t.dtype, dtypes.float32)
+    self.assertEqual(t.item(), 2.0)
 
   def test_unbound_variable_tensor(self):
-    # TODO: Tensor creation from unbound variable should assert
-    # with self.assertRaises(AssertionError): Tensor(Variable("u", 1, 10))
-    t = Tensor(Variable("u", 1, 10))
-    self.assertRaises(KeyError, t.item)  # today it builds silently and fails at execution
+    # an unbound variable schedules fine, but can't execute
+    with self.assertRaisesRegex(RuntimeError, "unbound"): Tensor(Variable("u", 1, 10)).item()
+    with self.assertRaisesRegex(RuntimeError, "unbound"): (Tensor(Variable("u", 1, 10)) + 1).item()
+    # bound variables in an expression are fine
+    self.assertEqual(Tensor(Variable("u", 1, 10).bind(2) + 1).item(), 3)
 
   def test_shrink_beyond_buffer_variable(self):
     # TODO: shrink by a variable whose vmax exceeds the dim should fail at build, today only CHECK_OOB=1 rejects it

test/unit/test_multitensor.py

@@ -78,8 +78,9 @@ class TestMultiTensor(unittest.TestCase):
     self.assertEqual(Y.device, devices_2)
     np.testing.assert_equal(X.numpy(), Y.numpy())
 
-    with self.assertRaises(AssertionError):
-      _ = Tensor(X.uop, dtype=dtypes.float)
+    Z = Tensor(X.uop, dtype=dtypes.float)
+    self.assertEqual(Z.dtype, dtypes.float)
+    np.testing.assert_equal(Z.numpy(), [1.0, 2.0])
 
   def test_sharded_arange(self):
     sharded_arange = Tensor.arange(1000).clone().shard(devices_2, 0)

tinygrad/tensor.py

@@ -69,9 +69,9 @@ class Tensor(RandMixin):
 
     # create a UOp from the different types of inputs
     if isinstance(data, UOp):
-      assert _dtype is None or _dtype==data.dtype or data.dtype==dtypes.index, f"dtype mismatch: {_dtype} vs {data.dtype}"
       # if data is dtype.index that means that this is a symbolic int and we need to lower it to something we can make a Tensor out of
       if data.dtype == dtypes.index: data = _index_to_concrete_int(data)
+      if _dtype is not None: data = data.cast(_dtype)
     elif data is None:
       data = UOp.const(_dtype or dtypes.default_float, 0)
     elif isinstance(data, get_args(ConstType)):

tinygrad/uop/ops.py

@@ -1154,7 +1154,9 @@ class ProgramInfo:
     local_size = tuple([sym_infer(sz, var_vals) for sz in self.local_size]) if self.local_size is not None else None
     return global_size, local_size
 
-  def vals(self, var_vals:dict[str, int]): return tuple(var_vals[k.expr] if k.expr not in self.runtimevars else None for k in self.vars)
+  def vals(self, var_vals:dict[str, int]) -> tuple[int|None, ...]:
+    try: return tuple(var_vals[k.expr] if k.expr not in self.runtimevars else None for k in self.vars)
+    except KeyError as e: raise RuntimeError(f"unbound Variable {e} used by {self.function_name}") from None
 
   @staticmethod
   def from_sink(sink:UOp, aux:tuple=()) -> ProgramInfo: