Unconditional forcing of ``CHECKED_HASH`` invalidation was introduced in
3.7.0 in bpo-29708. The change is bad, as it unconditionally overrides
*invalidation_mode*, even if it was passed as an explicit argument to
``py_compile.compile()`` or ``compileall``. An environment variable
should *never* override an explicit argument to a library function.
That change leads to multiple test failures if the ``SOURCE_DATE_EPOCH``
environment variable is set.
This changes ``py_compile.compile()`` to only look at
``SOURCE_DATE_EPOCH`` if no explicit *invalidation_mode* was specified.
I also made various relevant tests run with explicit control over the
value of ``SOURCE_DATE_EPOCH``.
While looking at this, I noticed that ``zipimport`` does not work
with hash-based .pycs _at all_, though I left the fixes for
subsequent commits.
To support reproducible builds, the setting of of SOURCE_DATE_EPOCH triggers the py_compile module -- and by extension, compileall -- to forcibly compile with hash-based .pyc files. This eliminates the possibility of timestamp-based .pyc files which vary between builds.
Python now supports checking bytecode cache up-to-dateness with a hash of the
source contents rather than volatile source metadata. See the PEP for details.
While a fairly straightforward idea, quite a lot of code had to be modified due
to the pervasiveness of pyc implementation details in the codebase. Changes in
this commit include:
- The core changes to importlib to understand how to read, validate, and
regenerate hash-based pycs.
- Support for generating hash-based pycs in py_compile and compileall.
- Modifications to our siphash implementation to support passing a custom
key. We then expose it to importlib through _imp.
- Updates to all places in the interpreter, standard library, and tests that
manually generate or parse pyc files to grok the new format.
- Support in the interpreter command line code for long options like
--check-hash-based-pycs.
- Tests and documentation for all of the above.
The concept of .pyo files no longer exists. Now .pyc files have an
optional `opt-` tag which specifies if any extra optimizations beyond
the peepholer were applied.
Elvis Pranskevichus
Bernhard M. Wiedemann
Benjamin Peterson
Serhiy Storchaka
Brett Cannon
Barry Warsaw
Berker Peksag
Christian Heimes
Meador Inge