Also remove the APT PPA

Mypy 0.790 complains that:

apt/package.py:473: error: Variable "builtins.NotImplemented" is not valid as a type
apt/package.py:473: note: See https://mypy.readthedocs.io/en/latest/common_issues.html#variables-vs-type-aliases

This worked fine in 0.782.

As a workaround, use Any instead of NotImplemented. Ugh

See https://github.com/python/mypy/issues/4791 for more
information.

Fix some issues reported by lintian

See merge request apt-team/python-apt!49

Fix sphinx docs

See merge request apt-team/python-apt!51

Fix a trivial "unused comment" complaint from mypy

Squash lots of warnings about improper C syntax by switching the docs
to use the sphinx cpp domain instead (which also required switching
c:data definitions to cpp:var as the latter domain lacks the "data"
definition).

The highlightlang directive was deprecated in favour of highlight.
Also fix a warning about parsing a code-block (which is actually an
e-mail snippet).

The HashStringList definition is already automatically including
:members: in its output, so the autoattribute:: redundantly re-defines
the "usable" attribute, leading to the warning.

At some point in its history, sphinx switched from using contents.rst to
index.rst as the master document and now warns that if projects aren't
using index.rst they need to explicitly set master_doc in their
configuration.

The defindex.html template has been obsolete for yonks and has been
removed, unremoved, deprecated, and finally (definitely?) removed as
of sphinx 3. See https://github.com/sphinx-doc/sphinx/issues/2986 for
the sordid history :)

Fixes: lintian: out-of-date-standards-version
See-also: https://lintian.debian.org/tags/out-of-date-standards-version.html

Fixes: lintian: debian-changelog-line-too-long
See-also: https://lintian.debian.org/tags/debian-changelog-line-too-long.html

Fixes: lintian: file-contains-trailing-whitespace
See-also: https://lintian.debian.org/tags/file-contains-trailing-whitespace.html

LP: #1874880

This includes, but might not be limited to:

- explicit version checks
- try/except ImportError wrapping of typing imports
- referencing imported types like `Type  # pyflakes` because
  older pyflakes stumbled upon them only being used in `# type`
  comments

Doing this via pybuild is somewhat nasty, as it does not
allow us to move all the common files into the common
package itself, so we have to hack around that.

I'd like to more declaratively state which files belong
into common, or for pybuild to figure that out itself
(it ain't hard), but meh, what can I do?

This fixes the problem where the wildcard that was
matching debug symbols "d-*" (formerly dm-*) also is
matching kfreebsd-, and hence caused FTBFS on freebsd.

Closes: #958118

Stop building for Python 2

See merge request apt-team/python-apt!48

Aside from dropping Python2 support, this also moves the
documentation from /usr/share/doc/python-apt to
/usr/share/python-apt-doc, which might be unfortunate.

The next step, in 2.1.1, will be to actually do code changes
to take advantage of Python 3.

Closes: #937579

[py2removal] Use pyflakes3 instead of pyflakes

See merge request apt-team/python-apt!46

python3-all-dev depends on python3-all, yet lintian bugs
us about runtime-test-file-uses-supported-python-versions-without-python-all-build-depends
- meh.

Gbp-Dch: ignore

Decode locale-encoded descriptions.

See merge request apt-team/python-apt!47

The translated description returned by libapt-pkg is, unlike other
fields, locale-encoded (see apt-pkg/deb/debrecords.cc). As such, try
decoding that description with the current locale.

python-apt currently uses (python 3) pycodestyle and (python 2) pyflakes
for code quality checks. It is one of the last users of pyflakes and
dropping this dependency should allow further removals of python 2
packages.

This necessitated two small fixes where python2-only builtins are
referred to (even when protected by version guards) to prevent pyflakes3
from identifying them as errors.

mypy 0.770 now requires that we explictly specify mutate_flag,
which smells like a bug to me. :/

Forwarded: https://github.com/python/typeshed/issues/3881

aptsources: Allow non-existent `source.list` file

See merge request apt-team/python-apt!45

Apt itself allows for the `sources.list` file to not exist,
and so should aptsources.

For example, the `puppetlabs/apt` Puppet module changed its
purging behavior for `sources.list` file to simply delete
the file instead of leaving a file with a comment as it
previously did. As a result, everyone enforcing source entry
purging via the Puppet module as a result receives an unnecessary
warning when this Python module is used prior to this change.

Improve type annotations for apt_pkg.TagFile and apt_pkg.TagSection

See merge request apt-team/python-apt!44