Per https://github.com/pantsbuild/pex/pull/734, I think our bit-for-bit reproducibility of Pex was a lie. Adding

--disable-cache

to the integration test, then running

tox -e py37-integration -- -k test_reproducible_build

, results in 4 failures like this:

E                       AssertionError: /var/folders/hm/qjjq4w3n0fsb07kp5bxbn8rw0000gn/T/tmplhw07ys7/pex0/.deps/future-0.17.1-py3-none-any.whl/future-0.17.1.dist-info/RECORD and /var/folders/hm/qjjq4w3n0fsb07kp5bxbn8rw0000gn/T/tmplhw07ys7/pex1/.deps/future-0.17.1-py3-none-any.whl/future-0.17.1.dist-info/RECORD have different content.
E                       assert [b'../../bin/...D,,\r\n', ...] == [b'../../bin/f...D,,\r\n', ...]
E                         At index 8 diff: b'future-0.17.1.dist-info/direct_url.json,sha256=7F4J29u5EP7AqxsrmEsapLhIiL0dY8l5GZr40Pzrp_0,229\r\n' != b'future-0.17.1.dist-info/direct_url.json,sha256=lz3ZispHJTXqJGCefZuoDn5ea6grUqSqOiI1savmViE,229\r\n'

Ok, great. Thanks for digging that up with a repro. I'll look into that and

SOURCE_DATE_EPOCH