Revert a private API in the HTML formatter

[kurtmckee]

This should revert the behavior of the function without losing the overall caching behavior that was intended.

In addition to running the unit tests, I confirmed identical SHA1 checksums for before-and-after HTML documents generated with (and without) the -O noclasses option.

@asottile, please confirm that this fixes #1644. Thanks!

[asottile]

yep! can confirm -- thanks!

$ git clone git@github.com:chriskuehl/pygments-ansi-color
Cloning into 'pygments-ansi-color'...
remote: Enumerating objects: 92, done.
remote: Total 92 (delta 0), reused 0 (delta 0), pack-reused 92
Receiving objects: 100% (92/92), 21.86 KiB | 621.00 KiB/s, done.
Resolving deltas: 100% (46/46), done.

$ cd pygments-ansi-color/

$ tox --devenv venv
py create: /tmp/pygments-ansi-color/venv
py installdeps: -rrequirements-dev.txt
py develop-inst: /tmp/pygments-ansi-color
py installed: appdirs==1.4.4,attrs==20.3.0,cfgv==3.2.0,coverage==5.3.1,distlib==0.3.1,filelock==3.0.12,identify==1.5.10,iniconfig==1.1.1,nodeenv==1.5.0,packaging==20.8,pluggy==0.13.1,pre-commit==2.9.3,py==1.10.0,Pygments==2.7.3,-e git+git@github.com:chriskuehl/pygments-ansi-color@6c86544c34254c03845c6c122468bb102c70e3eb#egg=pygments_ansi_color,pyparsing==2.4.7,pytest==6.2.1,PyYAML==5.3.1,six==1.15.0,toml==0.10.2,virtualenv==20.2.2
___________________________________ summary ____________________________________
  py: skipped tests
  congratulations :)

$ venv/bin/pip install git+https://github.com/kurtmckee/pygments@fix-1644
Collecting git+https://github.com/kurtmckee/pygments@fix-1644
  Cloning https://github.com/kurtmckee/pygments (to revision fix-1644) to /tmp/pip-req-build-6medy8pu
Building wheels for collected packages: Pygments
  Building wheel for Pygments (setup.py) ... done
  Created wheel for Pygments: filename=Pygments-2.7.3.dev20201229-py3-none-any.whl size=951640 sha256=13c0bc3a35db5ea9e3740647b42d8a1acefcb07f05050b9ba3bf1bafc1217233
  Stored in directory: /tmp/pip-ephem-wheel-cache-ypriv75o/wheels/5a/f4/4f/e090c5a32f60b106eea9c6a23e5d75fc866eae9b6f24b526c1
Successfully built Pygments
Installing collected packages: Pygments
  Attempting uninstall: Pygments
    Found existing installation: Pygments 2.7.3
    Uninstalling Pygments-2.7.3:
      Successfully uninstalled Pygments-2.7.3
Successfully installed Pygments-2.7.3.dev20201229
WARNING: You are using pip version 20.2.4; however, version 20.3.3 is available.
You should consider upgrading via the '/tmp/pygments-ansi-color/venv/bin/python -m pip install --upgrade pip' command.

$ venv/bin/pytest tests
============================= test session starts ==============================
platform linux -- Python 3.8.5, pytest-6.2.1, py-1.10.0, pluggy-0.13.1
rootdir: /tmp/pygments-ansi-color
collected 30 items                                                             

tests/pygments_ansi_color_test.py ..............................         [100%]

============================== 30 passed in 0.07s ==============================

[Anteru]

@kurtmckee Thanks for the timely fix, much appreciated! I'll merge this for now, but I'd like to encourage @asottile to come up with either an alternative solution or a proposal for an API which would prevent this kind of breakage in the future. I definitely don't want people to rely on private APIs, and if it's generally useful (or can be made generally useful), we should move it to some well-defined public API.