PEP 656: Platform Tag for Linux Distributions Using Musl

pep-0656.rst

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+PEP: 656
+Title: Platform Tag for Linux Distributions Using Musl
+Author: Tzu-ping Chung <uranusjr@gmail.com>
+Sponsor: Brett Cannon <brett@python.org>
+PEP-Delegate: TBD
+Discussions-To: https://discuss.python.org/t/7165
+Status: Draft
+Type: Informational
+Content-Type: text/x-rst
+Created: 2021-03-17
+
+
+Abstract
+========
+
+This PEP proposes a new platfrom tag series ``musllinux`` for
+binary Python package distributions for a Python installation linked
+against musl on a Linux distribution. The tag works similarly to the
+"perennial manylinux" platform tags specified in :pep:`600`, but
+targeting platforms based on musl instead.
+
+
+Motivation
+==========
+
+With the wide use of containers, distributions such as Alpine Linux,
+[alpine]_ have been gaining more popularity than ever. Many of them
+based on musl, [musl]_ a different libc implementation from glibc, and
+therefore cannot use the existing ``manylinux`` platform tags. This
+means that Python package projects cannot deploy binary distributions
+on PyPI for them. Users of such projects demand build constraints from
+those projects, putting unnecessary burden on project maintainers.
+
+
+Rationale
+=========
+
+According to the documentation, musl has a stable ABI, and maintains
+backwards compatibility, [musl-compatibility]_ [compare-libcs]_ so a
+binary compiled against an earlier version of musl is guaranteed to
+run against a newer musl runtime. [musl-compat-ml]_ Therefore, we use
+a scheme similar to the glibc-version-based manylinux tags, but
+against musl versions instead of glibc.
+
+Logic behind the new platform tag largely follows :pep:`600`, and
+require wheels using this tag make similar promises. Please refer to
+the PEP for more details on rationale and reasoning behind the design.
+
+
+Specification
+=============
+
+Tags using the new scheme will take the form::
+
+    musllinux_${MUSLMAJOR}_${MUSLMINOR}_${ARCH}
+
+Distributions using the tag make similar promises to those discribed
+in :pep:`600`, including:
+
+1. The distribution works on any mainstream Linux distributions with
+   musl version ``${MUSLMAJOR}.${MUSLMINOR}`` or later.
+2. The distribution's ``${ARCH}`` matches the return value of
+   ``sysconfig.get_platform()`` on the host system.
+
+Example values::
+
+    musllinux_1_1_x86_64   # musl 1.1 running on x86-64.
+    musllinux_1_2_aarch64  # musl 1.2 running on ARM 64-bit.
+
+The value can be formatted with the following Python code::
+
+    import sysconfig
+
+    def format_musllinux(musl_version: tuple[int, int]) -> str:
+        os_name, sep, arch = sysconfig.get_platform().partition("-")
+        assert os_name == "linux" and sep, "Not a Linux"
+        arch = arch.replace("-", "_")
+        return f"musllinux_{musl_version[0]}_{musl_version[1]}_{arch}"
+
+It is recommended for Python package repositories, including PyPI, to
+accept platform tags matching the following regular expression::
+
+    musllinux_([0-9]+)_([0-9]+)_([^-]+)
+
+Python package repositories may impose additional requirements to
+reject Wheels with known issues, including but not limited to:
+
+* A ``musl_1_1`` wheel containing symbols only available in musl 1.2.
+* Wheel that depends on external libraries not considered generally
+  available to the intended audience of the package index.
+* A platform tag claiming compatibility to a non-existent musl version
+  (like ``musl_9000_0``).
+
+Such policies are ultimately up to individual package repositories.
+It is not the author's intention to impose restrictions to the
+maintainers.
+
+
+Backwards Compatibility
+=======================
+
+There are no backwards compatibility concerns in this PEP.
+
+
+Rejected Ideas
+==============
+
+Create a platform tag based specifically for Alpine Linux
+---------------------------------------------------------
+
+Past experience on the ``manylinux`` tag series shows this approach
+would be too costly time-wise. The author feels the "works well with
+others" rule both is more inclusive and works well enough in practice.
+
+
+References
+==========
+
+.. [alpine] https://alpinelinux.org/
+
+.. [musl] https://musl.libc.org
+
+.. [musl-compatibility] https://wiki.musl-libc.org/compatibility.html
+
+.. [compare-libcs] https://www.etalabs.net/compare_libcs.html
+
+.. [musl-compat-ml] https://mail.python.org/archives/list/distutils-sig@python.org/message/VRXSTNXWHPAVUW253ZCWWMP7WDTBAQDL/
+
+
+Copyright
+=========
+
+This document is placed in the public domain or under the
+CC0-1.0-Universal license, whichever is more permissive.
+
+
+..
+   Local Variables:
+   mode: indented-text
+   indent-tabs-mode: nil
+   sentence-end-double-space: t
+   fill-column: 70
+   coding: utf-8
+   End: