bug#15552: 24.3.50; epa-file-cache-passphrase-for-symmetric-encryption not respected with GnuPG 2.x

[Stefan Monnier]

>>> It used to work like that with gpg1.  However, gpg2's implementation
>>> choice is that it does not leak the indication that gpg2 (actually
>>> gpg-agent) requires passphrase and it does not allow other tools than
>>> pinentry to inject passphrase.
>> IOW epa-file-cache-passphrase-for-symmetric-encryption only works for
>> gpg1 and not for gpg2?
> s/works/has no effect/

Same difference.  The docstring should prominently say that this var
doesn't work with gpg2 because gpg2 does not let Emacs cache the
passphrase (IIUC we can't make this var effective without changes in
gpg2).

> I didn't get the question correctly, then.
> Look at the matrix of (info "(epa) Caching Passphrases"), check when a
> user is suggested to "set up elisp passphrase cache".

That repeats the fact that symmetric encryption is handled differently
but still doesn't help me understand why.


        Stefan