Multiple return type hint with @ti.func not working on 1.7

[kmarchais]

Hello

Describe the bug
Since updating taichi to 1.7, I can't use type hinting for return tuple using a @ti.func, it was working under 1.6. Same behaviour with @ti.pyfunc. It works with @ti.real_func though.
Is it the expected behaviour?

To Reproduce

import taichi as ti
import taichi.math as tm

ti.init(arch=ti.cpu, debug=True)


@ti.func
def foo() -> tuple[int, tm.vec3]:
    a = 1
    b = tm.vec3(1.0, 2.0, 3.0)
    return a, b


@ti.kernel
def kernel() -> tuple[int, tm.vec3]:
    return foo()


print(kernel())

Log/Screenshots

$ python .\test-new-dev.py
[Taichi] version 1.7.0, llvm 15.0.1, commit 2fd24490, win, python 3.11.7  
[Taichi] Starting on arch=x64
Traceback (most recent call last):
  File "C:\Users\kevin\dev\taichi\test-new-dev.py", line 19, in <module>  
    print(kernel())
          ^^^^^^^^
  File "C:\Users\kevin\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\kernel_impl.py", line 1107, in wrapped
    raise type(e)("\n" + str(e)) from None
taichi.lang.exception.TaichiCompilationError:
File "C:\Users\kevin\dev\taichi\test-new-dev.py", line 16, in kernel:     
    return foo()
           ^^^^^
File "C:\Users\kevin\dev\taichi\test-new-dev.py", line 11, in foo:        
    return a, b
    ^^^^^^^^^^^
Traceback (most recent call last):
  File "C:\Users\kevin\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\ast\ast_transformer_utils.py", line 27, in __call__
    return method(ctx, node)
           ^^^^^^^^^^^^^^^^^
  File "C:\Users\kevin\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\ast\ast_transformer.py", line 928, in build_Return
    ctx.return_data[i] = ti_ops.cast(ctx.return_data[i], return_type)     
    ~~~~~~~~~~~~~~~^^^
TypeError: 'tuple' object does not support item assignment
...

[bobcao3]

I don't think we supports the standard square bracket type hints...

[lin-hitonami]

I don't think we supports the standard square bracket type hints...

We do support them in v1.7.0. Maybe we forgot to add support for the ti.func. However the type hint of ti.func isn't mandatory. You can remove the return type hint for now.

[kmarchais]

Indeed, it works without type hinting. However, I would still prefer to use type hinting though.
Temporarily I switched my func to real_func.