Props blacklist

[alexcjohnson]

Fixes plotly/dash-core-components#440

Pares down the attributes of dash component classes on the Python side by doing two things:

• Remove the MutableMapping inheritance - we weren't using any of the mixins from that class anyway, except in tests. This stops setting attributes: clear, get, items, keys, pop, popitem, setdefault, update, values - all of these are now allowable as prop names. We still set the magic methods of the mapping interface.
• Prefix a couple of other methods (traverse and traverse_with_paths) with underscores, so these are allowable as well.

Then what's left we blacklist: during extract-meta, if any prop has a leading underscore or matches one of the remaining disallowed names, we fail (not just print a warning) and refuse to generate the python file. The names we forbid are:

• UNDEFINED
• REQUIRED
• to_plotly_json
• available_properties
• available_wildcard_properties

These are all used within generated components, or (in the case of to_plotly_json) in other packages, so it would be difficult to allow these without forcing all packages to be rebuilt. Fortunately I don't see these as particularly valuable prop names (unlike, say, values, items, and some of the other MutableMapping methods)

Error messages look like:

ERROR: "_foo" matches forbidden prop name pattern: /^_.*$/

extract-meta failed.


Error generating metadata in dash_core_components (status=0)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
...

• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR
• I have added entry in the CHANGELOG.md

[alexcjohnson]

Kind of a nice side effect, IMO, that components are now no longer always equal to each other - though I don't know why this would come up...

[alexcjohnson]

So that you can run the tests from any working directory, not just the repo root.

[alexcjohnson]

we don't write a response if the error was severe enough for us to set failed - this causes generate_components to fail as well.

[byronz]

💃 looks great, thanks Alex