closes bpo-31650: PEP 552 (Deterministic pycs) implementation (#4575)

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.

1 files changed, 6 insertions, 0 deletions

diff --git a/Doc/glossary.rst b/Doc/glossary.rst
index ba4d300..e875e1f 100644
--- a/Doc/glossary.rst
+++ b/Doc/glossary.rst
@@ -458,6 +458,12 @@ Glossary
       is believed that overcoming this performance issue would make the
       implementation much more complicated and therefore costlier to maintain.
 
+
+   hash-based pyc
+      A bytecode cache file that uses the the hash rather than the last-modified
+      time of the corresponding source file to determine its validity. See
+      :ref:`pyc-invalidation`.
+
    hashable
       An object is *hashable* if it has a hash value which never changes during
       its lifetime (it needs a :meth:`__hash__` method), and can be compared to