feat: export .from() etc. with behavior similar to dplyr::across()

[maelle]

Fix #1435

A drawback: the tree "nei" functions are actually only for index sequences but I let them output the same message. Is that bad?

Also, the help link does not work for me but it looks correct, maybe just a problem with my IDE version? I'd be grateful if you could try it on your side.

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[krlmlr]

Thanks, will try locally.

These days, I'd use generated code instead of clever code like this. One drawback is that environment(.from) is not the igraph environment; to achieve this, we'd need even cleverer code.

[krlmlr]

Would you like to add examples of correct usage, or a link to the help topic where they are described? Perhaps even merge with that existing help topic (if it, well, exists)?

[maelle]

These days, I'd use generated code instead of clever code like this. One drawback is that environment(.from) is not the igraph environment; to achieve this, we'd need even cleverer code.

Do we need to tackle this here?

[maelle]

Ooooh https://roxygen2.r-lib.org/articles/rd-formatting.html?q=link#operators

[maelle]

Would you like to add examples of correct usage, or a link to the help topic where they are described? Perhaps even merge with that existing help topic (if it, well, exists)?

Painstakingly added the links. 😁

[krlmlr]

Let's remove the keywords internal at some point, shouldn't be a blocker for now.

[maelle]

I don't think they should be external though. Users should only get to them from the error message.