feat: setup.py redesign and helpers (#2433)

* feat: setup.py redesign and helpers

* refactor: simpler design with two outputs

* refactor: helper file update and Windows support

* fix: review points from @YannickJadoul

* refactor: fixes to naming and more docs

* feat: more customization points

* feat: add entry point pybind11-config

* refactor: Try Extension-focused method

* refactor: rename alt/inplace to global

* fix: allow usage with git modules, better docs

* feat: global as an extra (@YannickJadoul's suggestion)

* feat: single version location

* fix: remove the requirement that setuptools must be imported first

* fix: some review points from @wjacob

* fix: use .in, add procedure to docs

* refactor: avoid monkeypatch copy

* docs: minor typos corrected

* fix: minor points from @YannickJadoul

* fix: typo on Windows C++ mode

* fix: MSVC 15 update 3+ have c++14 flag

See <https://docs.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=vs-2019>

* docs: discuss making SDists by hand

* ci: use pep517.build instead of manual setup.py

* refactor: more comments from @YannickJadoul

* docs: updates from @ktbarrett

* fix: change to newly recommended tool instead of pep517.build

This was intended as a proof of concept; build seems to be the correct replacement.

See https://github.com/pypa/pep517/pull/83

* docs: updates from @wjakob

* refactor: dual version locations

* docs: typo spotted by @wjakob

tools/setup_global.py.in

@@ -0,0 +1,53 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# Setup script for pybind11-global (in the sdist or in tools/setup_global.py in the repository)
+# This package is targeted for easy use from CMake.
+
+import contextlib
+import glob
+import os
+import re
+import shutil
+import subprocess
+import sys
+import tempfile
+
+# Setuptools has to be before distutils
+from setuptools import setup
+
+from distutils.command.install_headers import install_headers
+
+class InstallHeadersNested(install_headers):
+    def run(self):
+        headers = self.distribution.headers or []
+        for header in headers:
+            # Remove pybind11/include/
+            short_header = header.split("/", 2)[-1]
+
+            dst = os.path.join(self.install_dir, os.path.dirname(short_header))
+            self.mkpath(dst)
+            (out, _) = self.copy_file(header, dst)
+            self.outfiles.append(out)
+
+
+main_headers = glob.glob("pybind11/include/pybind11/*.h")
+detail_headers = glob.glob("pybind11/include/pybind11/detail/*.h")
+cmake_files = glob.glob("pybind11/share/cmake/pybind11/*.cmake")
+headers = main_headers + detail_headers
+
+cmdclass = {"install_headers": InstallHeadersNested}
+$extra_cmd
+
+setup(
+    name="pybind11_global",
+    version="$version",
+    packages=[],
+    headers=headers,
+    data_files=[
+        ("share/cmake/pybind11", cmake_files),
+        ("include/pybind11", main_headers),
+        ("include/pybind11/detail", detail_headers),
+    ],
+    cmdclass=cmdclass,
+)