-------- Forwarded Message -------- Subject: F28 Self Contained Change: Avoid /usr/bin/python in RPM build Date: Tue, 9 Jan 2018 20:13:58 +0100 From: Jan Kurik jkurik@redhat.com Reply-To: Development discussions related to Fedora devel@lists.fedoraproject.org To: Development discussions related to Fedora devel@lists.fedoraproject.org, devel-announce@lists.fedoraproject.org

= Proposed Self Contained Change: Avoid /usr/bin/python in RPM build = https://fedoraproject.org/wiki/Changes/Avoid_usr_bin_python_in_RPM_Build

Change owner(s): * Petr Viktorin <python-devel at lists.fedoraproject.org> * Miro Hrončok <python-devel at lists.fedoraproject.org>

Deprecate, and later disable, running /usr/bin/python (as opposed to /usr/bin/python3 or /usr/bin/python2) during RPM build. Changes will be driven by Python SIG, but a few packages may fail to build (with the failure message providing an easy workaround).

== Detailed Description == === Motivation ===

Currently in Fedora (package names, executable names, etc.), python means Python 2. We would like to change it to mean Python 3, but to do that, we need to free it of the current meaning. This means explicitly using either "python2" or "python3" throughout Fedora. This is a multi-release effort tracked in Python SIG's "Finalizing Fedora Switch to Python3" document. This page describes a very focused subset of it.

Renaming packages (and associated changes to, for example, "Requires:" directives) is relatively straightforward, but making all Fedora-provided code avoid /usr/bin/python (as opposed to /usr/bin/python2) is both harder to achieve and harder to keep track of.

We would like to start deprecating /usr/bin/python (as opposed to /usr/bin/python2) at RPM build time. RPM build is a controlled environment: changes to it will not be felt by end users, breakages are almost immediately visible, and output of Koji builds can be nicely tracked and analyzed.

=== Specification ===

Python 2, when called as python or /usr/bin/python at RPM build time (as identified by the RPM_BUILD_ROOT environment variable), will print a deprecation warning to stderr. (Any program invoked during build that invokes /usr/bin/python will cause this warning as well.)

A new Taskotron check will be implemented to look for this warning and fail if it's found. We will look at the Taskotron results and work with packagers to switch to update the affected packages. (We'll look at the results to determine if we'll use automated pull requests, mass bug filing, or something else.)

The warning itself may cause some packages to fail to build, for example if a test relies on exact stderr contents. For these cases, it will be possible to turn the warning off using an environment variable, but we ask packagers that use of this workaround is tracked in Bugzilla. See Opt-Out below.

After all packages that BuildRequire python2 are re-built with this check passing, python will be switched to fail after printing the message.

The warning will not be effective if stderr output is hidden. So, after switching /usr/bin/python to fail, some packages may start failing to build. We will work with the packagers to fix these. (We'll look at results from the "warnings phase" to see how proactive we'll need to be here.)

The warning text will be:

DEPRECATION WARNING: python2 invoked with /usr/bin/python. Use /usr/bin/python3 or /usr/bin/python2 /usr/bin/python will be removed or switched to Python 3 in the future. If you cannot make the switch now, please follow instructions at https://fedoraproject.org/wiki/Changes/Avoid_usr_bin_python_in_RPM_Build#Qui...

(Using the Wiki link allows us to easily revise the instructions.)

=== Quick Opt-Out ===

In case switching to /usr/bin/python2 or /usr/bin/python3 is non-trivial, do these two things:

* Set the environment variable DISABLE_AMBIGUOUS_PYTHON_VERSION_WARNING=1 when calling /usr/bin/python * File a Bugzilla, and make it block our tracking bug (XXX - link)

All such bugs will need to be fixed before we make /usr/bin/python fail hard.

== Scope == * Proposal owners: Patch python2, write the Taskotron check, deal with warnings and failures.

* Other developers: Switch to using /usr/bin/python3 or /usr/bin/python2 explicitly at RPM build time (with help from Proposal owners if needed). Also tools that are invoked during build time of other packages that themselves use /usr/bin/python will need to be fixed.

* Release engineering: #7257: https://pagure.io/releng/issue/7257 Note: Depending on the timing, separate targeted rebuilds may be needed, but we can do these as Proven Packagers, no side-tags are required

* List of deliverables: N/A

* Policies and guidelines: Already existing "packages in Fedora ... MUST call the proper executable for the needed python major version directly, either /usr/bin/python2 or /usr/bin/python3 as appropriate" from Packaging:Python#Multiple_Python_Runtimes

* Trademark approval: N/A (not needed for this Change)