Generic strings/regex patterns in strings

Currently, we have str and LiteralStr. These don't do a good job expressing the range of values a string may have. Let's say we have the following function:

Email: TypeAlias = str

def send_email(email: Email) -> int:
    # Send an email
    ...

# passes
send_email("test@example.com")

# passes
send_email("badddd")

# passes even if unknown_var is only identified as `str`
send_email(unknown_var)

We could improve it by having something like this:

# This is a bad regex pattern, but you get the idea :)
Email: TypeAlias = str['[a-z0-9]+@[a-z0-9]+\.[a-z0-9]+']

def send_email(email: Email) -> int:
    # Send an email
    ...

# passes
send_email("test@example.com")

# fails
send_email("badddd")

# passes even if unknown_var is only identified as `str`
send_email(unknown_var)

A static type checker would be able to validate strings passed in by code. I would imagine this idea can be extended to Pattern and Match generics as well, but I haven't thought too deeply about them yet.

If we don't want to make str generic, we could add a new type to typing called StrPattern. We would need it anyways to backport to typing_extensions.

未指定实现文件或测试。首先检查现有对 str 和 LiteralStr 的处理方式，以及 typing_extensions 的约定；明确该功能使用通用 str 还是新的 StrPattern 类型，并在确定能够证明完成的测试之前，定义对字面量、变量、Pattern 和 Match 的预期行为。