[error] Improve kernel argument type mismatch error message

python/taichi/lang/impl.py

@@ -293,7 +293,7 @@ def make_constant_expr(val):
         else:
             assert False
     else:
-        raise ValueError(f'Bad constant scalar expression: {type(val)}')
+        raise ValueError(f'Invalid constant scalar expression: {type(val)}')
 
 
 def reset():

python/taichi/lang/kernel.py

@@ -190,14 +190,12 @@ def __init__(self, msg):
 
 class KernelArgError(Exception):
     def __init__(self, pos, needed, provided):
+        message = f'Argument {pos} (type={provided}) cannot be converted into required type {needed}'
+        super().__init__(message)
         self.pos = pos
         self.needed = needed
         self.provided = provided
 
-    def message(self):
-        return 'Argument {} (type={}) cannot be converted into required type {}'.format(
-            self.pos, str(self.needed), str(self.provided))
-
 
 def _get_global_vars(func):
     # Discussions: https://github.com/taichi-dev/taichi/issues/282
@@ -393,11 +391,11 @@ def func__(*args):
                 # Note: do not use sth like "needed == f32". That would be slow.
                 if id(needed) in real_type_ids:
                     if not isinstance(v, (float, int)):
-                        raise KernelArgError(i, needed, provided)
+                        raise KernelArgError(i, needed.to_string(), provided)
                     launch_ctx.set_arg_float(actual_argument_slot, float(v))
                 elif id(needed) in integer_type_ids:
                     if not isinstance(v, int):
-                        raise KernelArgError(i, needed, provided)
+                        raise KernelArgError(i, needed.to_string(), provided)
                     launch_ctx.set_arg_int(actual_argument_slot, int(v))
                 elif self.match_ext_arr(v, needed):
                     has_external_arrays = True

taichi/python/export_lang.cpp

@@ -88,6 +88,7 @@ void export_lang(py::module &m) {
       .def(py::init<Type *>())
       .def(py::self == py::self)
       .def("__hash__", &DataType::hash)
+      .def("to_string", &DataType::to_string)
       .def(py::pickle(
           [](const DataType &dt) {
             // Note: this only works for primitive types, which is fine for now.

tests/python/test_kernel_arg_errors.py

@@ -0,0 +1,16 @@
+import taichi as ti
+import pytest
+
+
+@ti.test(arch=ti.cpu)
+def test_pass_float_as_i32():
+    @ti.kernel
+    def foo(a: ti.i32):
+        pass
+
+    with pytest.raises(ti.KernelArgError) as e:
+        foo(1.2)
+
+    assert e.type is ti.KernelArgError
+    assert e.value.args[
+        0] == "Argument 0 (type=<class 'float'>) cannot be converted into required type i32"