bug#22533: Python bytecode reproducibility

[Ricardo Wurmus <rekado@elephly.net>]

Hi Gábor,

> Nix had this issue, it seems they have a python 3.5 solution, which
> should be easy to adopt: https://github.com/NixOS/nixpkgs/issues/22570.
> WDYT?

Here’s the patch for Nix:

  https://patch-diff.githubusercontent.com/raw/NixOS/nixpkgs/pull/22585.diff

Here are the relevant changes to the Python packages:

* Python 3.4

  substituteInPlace "Lib/py_compile.py" --replace "source_stats['mtime']" "(1 if 'DETERMINISTIC_BUILD' in os.environ else source_stats['mtime'])"
  substituteInPlace "Lib/importlib/_bootstrap.py" --replace "source_mtime = int(source_stats['mtime'])" "source_mtime = 1"

* Python 3.5

  substituteInPlace "Lib/py_compile.py" --replace "source_stats['mtime']" "(1 if 'DETERMINISTIC_BUILD' in os.environ else source_stats['mtime'])"
  substituteInPlace "Lib/importlib/_bootstrap_external.py" --replace "source_mtime = int(st['mtime'])" "source_mtime = 1"

* Python 3.6
  substituteInPlace "Lib/py_compile.py" --replace "source_stats['mtime']" "(1 if 'DETERMINISTIC_BUILD' in os.environ else source_stats['mtime'])"
  substituteInPlace "Lib/importlib/_bootstrap_external.py" --replace "source_mtime = int(st['mtime'])" "source_mtime = 1"


For all packages they set these environment variables:

  - set PYTHONHASHSEED=0 (for hashes of str, bytes and datetime objects)

  - set DETERMINISTIC_BUILD; for conditional patching of the timestamp
    for package builds.  The timestamp is not patched in ad-hoc
    environments, because that would mess with Python’s ability to
    determine whether to compile source files.

They also rebuild all bytecode (with the exception of lib2to3 because it
is Python 2 code) three times, once for each optimization level.

--8<---------------cut here---------------start------------->8---
+    # Determinism: rebuild all bytecode
+    # We exclude lib2to3 because that's Python 2 code which fails
+    # We rebuild three times, once for each optimization level
+    find $out -name "*.py" | $out/bin/python -m compileall -q -f -x "lib2to3" -i -
+    find $out -name "*.py" | $out/bin/python -O -m compileall -q -f -x "lib2to3" -i -
+    find $out -name "*.py" | $out/bin/python -OO -m compileall -q -f -x "lib2to3" -i -
--8<---------------cut here---------------end--------------->8---

--
Ricardo

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