@_nodoc attribute for hiding symbols from the symbol graph

[jack (Jack Lawrence)]

@ethankusters

Along these lines- I'm wondering if we should consider aligning this general design with SPI ? I can imagine wanting to hide certain symbols for general consumption of my documentation but expose them for certain audiences (just like with SPI).

I'm imagining something like: @_doc(docCategory) and then a corresponding --include-hidden-docs docCategory flag that can be passed to the symbol graph extract tool.

I like this, but I hesitate to add additional complexity when @spi already provides slicing for modules that present different views of public API to various clients. Do you have an example in mind?

In any case adding this flexibility is likely backwards-compatible if we wanted to introduce it later—we could interpret hidden and visible as special/default categories.