URLConfig preprocessor

[jmosbacher]

A few small improvements to URLConfigs, similar to #827 but a bit simpler implementation.

1. Formalizes the URL parsing as a string to AST and add reverse operation
2. Adds validate method that runs before the config is passed to the plugin.
3. Adds the ability to register preprocessors that can alter the URL/config before it is hashed.

Preprocessors are passed the config and return a new/same config. They are applied in order of higher precedence first.

[coveralls]

Coverage: 93.529% (-0.4%) from 93.91% when pulling bef1900 on url_config_preprocessor into eb0fe12 on master.

[JoranAngevaare]

@jmosbacher , looks good. In #827 you had a few tests, can you re-use those examples again?

Should we make the format_url_kwargs a default someday, or is xedocs already planned to use this feature?

Uhm, there are two self.format_url_kwargs methods? L193, L325 🤔

[jmosbacher]

@JoranAngevaare hmm you are right, now i realize why i left it as a draft for so long. I never got around to finishing polishing it and adding tests... Ill do that now.

[jmosbacher]

@JoranAngevaare I added some tests and documentation

[JoranAngevaare]

Nice work Yossi, I added a test to assert I understand it well.

Two final requests that I think would be useful for dummies like me:

• Add a preprossor_descr(cls) like protocol_descr(cls) and
• show(cls), that shows the overall state preprocessor + protocol (what is registered, what precedence is associated to each preprocessor, where is the code that adds it). We can add the output of that to the autodocs a la plugin tree, which would also solve URL protocols would benifit from autogenerated page #1111. The autodocs I can also do and/or make a separated PR for it

[jmosbacher]

Good idea. I added methods for the preprocessor as well as a print_summary method that prints both

[jmosbacher]

@JoranAngevaare did you want to already add the autodoc feature to this PR before its merged?

[JoranAngevaare]

@jmosbacher let's do it in a seperate PR, nice work Yossi, thanks!