sage_setup will be used by the build system of various distribution packages (#29705).

So we make it a regular distribution package itself, with sources in pkgs/sage-setup/ (#31577) and install it with pip.

The actual Python source files are not moved because sage_setup takes part in Sage doctesting (see #31577).

sagelib's setup.py will no longer install sage_setup.

sage-setup will become a build-system requires of sagemath-standard (declared in pyproject.toml)

Follow-up:

• sage_setup: Do not fail if sage.env, sage.* are not available #29924: Do not fail if sage.env, sage.* are not available

References:

python - pip ignores dependency_links in setup.py - Stack Overflow
https://stackoverflow.com/questions/12518499/pip-ignores-dependency-links-in-setup-py

dependency_links flag ignored when package exists on PyPI · Issue #987 · pypa/setuptools
pypa/setuptools#987

Suggest alternatives for --process-dependency-links · Issue #6162 · pypa/pip
pypa/pip#6162

PEP 508 -- Dependency specification for Python Software Packages | Python.org
https://www.python.org/dev/peps/pep-0508/#pep440

PEP 440 -- Version Identification and Dependency Specification | Python.org
https://www.python.org/dev/peps/pep-0440/#local-version-segments

Depends on #32046

CC: @kiwifb @jhpalmieri @dimpase

Component: build

Keywords: sd111

Author: Matthias Koeppe

Branch/Commit: f84730e

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29847