Integrate from __future__ import annotations

[Repiteo]

• Requires Remove Python 3.6 support #4642

A conservative implementation of integrating from __future__ import annotations in the codebase. Updates all instances where type hints could utilize new syntax, utilizing newly added Ruff rules to find & adjust said instances. The resulting type-hints are much cleaner, even granting functionality which otherwise require 3.9 or 3.10 as their minimum Python version:

# Before
def some_function(env: "SConsEnvironment") -> Optional[Tuple[List[str], Union[int, float]]]:

# After
def some_function(env: SConsEnvironment) -> tuple[list[str], int | float]] | None:

As a result of this new implementation, the hacky workarounds for forward-declaring types will no longer be necessary. Namely, sctyping.py is no longer necessary & has been removed. Instead, one should use from typing import TYPE_CHECKING & resolve imports like any other.

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There's a more involved alternative of this PR that adds from __future__ import annotations as a required import instead, making it appear on ALL scripts in the codebase. While it's arguably a "better" option, it would also create significantly more noise in the changelog. If this approach were to be taken, it'd have to be part of a wider refactor.

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt and RELEASE.txt (and read the README.rst).
• I have updated the appropriate documentation

[mwichmann]

Not sure we should ditch sctypes - be good to have a standard place for SCons-specific type combinations. For example, a ton of environment methods take an argument that's either a pathname string, or a file node, or a list of pathname strings and/or file nodes. That one is always going to be awkward to describe, even if we can stop using Union.

[mwichmann]

Not sure we should ditch sctypes - be good to have a standard place for SCons-specific type combinations. For example, a ton of environment methods take an argument that's either a pathname string, or a file node, or a list of pathname strings and/or file nodes. That one is always going to be awkward to describe, even if we can stop using Union.

oops, I conflated sctypes and sctyping. never mind....

[mwichmann]

It's a pain that after years of requests, GitHub still doesn't support some form of stacked PRs. I've tried some external solutions to this, and frankly, they were unusable for the kind of workflow SCons uses.

[mwichmann]

Looks good!

[bdbaddog]

Good work. Thanks!