embark-related parsing problems when multiple citekeys

[bdarcus]

Am unsure why this would turn up as a bug at this point, given how many people use this package, and how long that code has been stable.

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I ran into one more issue, which I thought I would like to report here. It affects multiple functions in the citar-citation-map, and has to do with the way they interact with citar-citation targets and citar-embark package.

Let me explain the problem by taking citar-copy-reference function as a specific example. This function accepts a list of citekeys, whose formatted references are to be inserted in the current buffer. When it receives its argument from citar--select-multiple or via an embark action on a citar-key target, all works well. But if the argument is from a citar-citation target with multiple keys, then citar-copy-reference fails to find the relevant bibliography entries.

I believe, the reason is that a citar-citation target produces a string obtained by concatenating individual keys with the " & " separator as done by the citar--stringify-keys function. Thus citar-copy-reference needs to unstringify the keys first, but its current implementation does not do this.

To give a concrete example, if citar-copy-reference is applied to the citar-citation target that corresponds to the LaTeX citation \cite{key1,key2}, then its argument becomes ("key1 & key2") instead of ("key1" "key2").

The problem can be fixed by unstringifying the argument first, e.g., by pre-processing it as follows:

(setq citekeys (mapcan #'citar--unstringify-keys citekeys))

The same issue, in fact, applies to functions citar-open, citar-open-links, citar-open-files, and citar-open-notes, each of which fails, in my case at least, to act on a citar-citation target with multiple keys.

Originally posted by @kslutsky in https://github.com/emacs-citar/citar/issues/834#issuecomment-2196233740