fix(decorations): expand pgfkeys internals in error msg

[muzimuzhi]

Motivation for this change

Implementation note:
Since \pgfkeyscurrentname would already been fully expanded in testers \pgfifdecoration and \pgfifmetadecoration, fully expansion, compared to one-step expansion, is also safe here.

Fixes #1082

Checklist

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• Code changes are licensed under GPLv2 + LPPLv1.3c
• Documentation changes are licensed under FDLv1.2

[muzimuzhi]

Please don't merge. I need check a thing. \pgfexpl@exp@args@@Ne seems not sufficient here.

[muzimuzhi]

Please don't merge. I need check a thing. \pgfexpl@exp@args@@Ne seems not sufficient here.

Unfortunately, my last commit 7943d07 is not a solution.

Here we face a usage \pgfkeys{key={arg1}{arg2}} and what's needed is to fully expand arg1 and leave arg2 unchanged before \pgfkeys expands. Hence

• \pgfexpl@exp@args@@Ne\pgfkeys{key={arg1}{arg2}} is wrong because it also expands arg2.
• All the existing /.expand xxx handlers can't help because they all treat keys as a single one arg.

To continue with \pgfexpl@exp@args@@Ne / \exp_args:Ne, arg2 should be wrapped by an \unexpanded:

\pgfexpl@exp@args@@Ne\pgfkeys{key={arg1}{\unexpanded{arg2}}}

Edit: Or, redefine /errors/unknown key and the like to always expand the arg representing "current key". Cons: may lead to less helpful error messages.

[ilayn]

Put it into another single key say errors/unknown key expanded that has /.code/expand once={{/pgf/decoration/\pgfkeyscurrentname}{#####1}} or whichever number is needed such that error message can be controlled. since nobody is using this there will be no backwards compatibility issue.

[hmenke]

If we need \unexpanded anyway we are better off using the more idiomatic /.expanded.

Suggested change

	% fully expand \pgfkeyscurrentname before being passed to
	% `/errors/unknown key`
	{\pgfexpl@exp@args@@Ne\pgfkeys{/errors/unknown
	key={/pgf/decoration/\pgfkeyscurrentname}{\unexpanded{#1}}}}},%
	{\pgfkeys{/errors/unknown
	key/.expanded={/pgf/decoration/\pgfkeyscurrentname}{\unexpanded{#1}}}}},%

[muzimuzhi]

oops, you're right. Should I remove pgfutil-expl.tex?

[hmenke]

Yes, please. We can do that later in a more coordinated fashion.

[muzimuzhi]

Unfortunatly,

• \pgfexpl@exp@args@@Ne\pgfkeys{key={... \pgfkeyscurrentname ...}} and
• \pgfkeys{key/.expanded={... \pgfkeyscurrentname ...}}

are different. In the first case, value of \pgfkeyscurrentname before this \pgfkeys is used. While in the second case, value of \pgfkeyscurrentname is updated to always hold .expanded, the name of just parsed handler.

This change caused the PR failed to fix the original issue, see also #1082 (comment).