Unasync'ed base dispatchers

[florimondmanca]

Refs #722

First smoll step towards unasync'ing HTTPX…: unasync AsyncDispatcher into SyncDispatcher. Allows us to setup the tooling and avoid impacting any public piece of API.

Mostly done, but marking as a draft as this is probably only worth considering once 0.11 is out…

[florimondmanca]

Just tried it out locally… the build works 👍

$ pip install "git+https://github.com/encode/httpx.git@unasynced-base-dispatchers"
$ python
Python 3.8.0 (default, Oct 16 2019, 18:21:21)
[Clang 11.0.0 (clang-1100.0.33.8)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import httpx
>>> r = httpx.get('https://www.google.com')
>>> httpx._sync.dispatch.base.SyncDispatcher
<class 'httpx._sync.dispatch.base.SyncDispatcher'>
>>> httpx.dispatch.base.SyncDispatcher
<class 'httpx._sync.dispatch.base.SyncDispatcher'>
>>>

[florimondmanca]

That's a bit funny, but listing unasync in the build-system.requires entry doesn't actually install it in a way that's available to the Python interpreter. I don't know when/where those dependencies are installed exactly — probably managed by pip in an opaque location…?

[florimondmanca]

Ah yes, the build will fail until python-trio/unasync@2c2c9b7 gets released. 😄 (I had a patched version of unasync installed locally.)

[florimondmanca]

Closing, we can revisit if/when moving forward on this in httpcore…