Error when from __future__ import annotations

[evan0greenup]

Describe the bug

When add from __future__ import annotation in the beginning of the source file, it will raise error.

To Reproduce

Just add from __future__ import annotation in any of example source files, the error will be thrown.

Log/Screenshots

(Skip)

$ python my_sample_code.py
[Taichi] mode=release
[Taichi] version 0.6.29, llvm 10.0.0, commit b63f6663, linux, python 3.8.3
...

Additional comments

In the future of Python release, from __future__ import annotations would be defaulted enabled. To get inspiration on how to support this, pydantic https://docs.pydantic.dev/latest/ would be a great resource to learn and research.