Add a RemoveFromParent() function as a convenience to returning RemovalSentinel.REMOVE.
Introduce a `deep_remove()` on CSTNode analogous to `deep_replace()` but for removing.
We used _visit_and_replace_children to implement deep_clone, which was already
bad since it relied on the implicit behavior of _visit_and_replace_children to
make a copy on visit. If we fix that behavior in the future, deep_Clone would
have broken. However, its even more broken, because nodes that subclass from
BaseLeaf define their _visit_and_replace_children as returning self. So, not
only is this a bad coupling, but its also broken. Implement deep_clone properly
here.
When parsing, we don't always fill in defaults unless we have a good reason to. That, coupled with the fact that we use dataclasses that allow you to set a default on creation instead of runtime construction means that we accidentally aliased a whole bunch of SimpleWhitespace nodes. Fix that by switching to the datalasses field() method which allows runtime evaluation. We do this by creating a simple (untyped, unfortunately) helper on CSTNode which makes for easier creation.
This introduces a few new gotchas (namely attribute access and a bug with
Union[Callable]), but it also removes a whole host of pyre-fixmes and gets us
updated to a release of pyre that came out after May.
Standardize on the convention that private modules (those we don't expect people to directly import) are prefixed with an underscore. Everything under a directory/module that has an underscore is considered private, unless it is re-exported from a non-underscored module. Most things are exported from libcst directly, but there are a few things in libcst.tool, libcst.codegen and libcst.metadata that are namedspaced as such.
