bug#20982: 25.0.50; GPG uses GUI dialog box to ask for passphrase

[Mark Karpov <markkarpov@openmailbox.org>]

Daiki Ueno <ueno@gnu.org> writes:

> Richard Stallman <rms@gnu.org> writes:
>
>> Maybe Emacs developers can cooperate with Werner Koch to set up a a
>> way GPG and Emacs can work together better for reading the passphrase.
>>
>> There is the option of using gpg-agent.
>
> We are already working on that, see:
> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=20550
>
> and the recent discussions on gnupg-devel mailing list, to make
> gpg-agent (and pinentry) respect the INSIDE_EMACS envvar:
> https://lists.gnupg.org/pipermail/gnupg-devel/2015-June/029915.html
>
> Now that all patches had landed in both GnuPG (2.1.x) and Emacs (git
> master), maybe people who demand on this feature could try it, so it can
> be safely backported to the GnuPG stable series?
>
> Regards,

I would like to try this. I have

  ~ $ gpg --version
  gpg (GnuPG) 2.1.6
  libgcrypt 1.6.3
  Copyright (C) 2015 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
  This is free software: you are free to change and redistribute it.
  There is NO WARRANTY, to the extent permitted by law.
  
  Home: ~/.gnupg
  Supported algorithms:
  Pubkey: RSA, ELG, DSA, ECDH, ECDSA, EDDSA
  Cipher: IDEA, 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH,
          CAMELLIA128, CAMELLIA192, CAMELLIA256
  Hash: SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
  Compression: Uncompressed, ZIP, ZLIB, BZIP2

…and Emacs built from git master (head: 8c81ac9 master ; Spelling fixes).

This doesn't seem to work out-of-the-box. What additional steps should
one undertake to get rid of the dialog box?