Empty hook raises error with label-specific message

[muzimuzhi]

Brief outline of the bug

Empty hook label is not supported so it raises an expandable error with label-specific message:

! LaTeX hooks Error: Empty code label on line 41. Using 'top-level' instead.

Empty hook is not supported too, but the raised error is the same as that for empty label, thus misleading. (At least the suggestion to using top-level hook name is wrong.)

Minimal example showing the bug

\RequirePackage{latexbug}       % <--should be always the first line (see CONTRIBUTING)!
\AddToHook{myhook}[]{code} % empty label
\AddToHook{}{code}         % empty hook
\UseName{@@end}

Log file (required) and possibly PDF file

latex2e-empty-hook-misleading-message.log

[muzimuzhi]

The parsing of dot-syntax in hooks and labels shares the same function \__hook_parse_label_default:n.

One possibility is to make that function absorb a new boolean argument (as a marker) and pass it to the function \__hook_parse_dot_label:n which would raise different errors (empty-label or empty-hook) depending on the value of that boolean.

latex2e/base/lthooks.dtx

Lines 3425 to 3442 in 11f2110

	\cs_new_protected:Npn \@@_normalize_hook_args:Nnn #1 #2 #3
	{
	\@@_normalize_hook_args_aux:Nn #1
	{
	{ \@@_parse_label_default:n {#2} }
	{ \@@_parse_label_default:n {#3} }
	}
	}
	\cs_new_protected:Npn \@@_normalize_hook_rule_args:Nnnnn #1 #2 #3 #4 #5
	{
	\@@_normalize_hook_args_aux:Nn #1
	{
	{ \@@_parse_label_default:n {#2} }
	{ \@@_parse_label_default:n {#3} }
	{ \tl_trim_spaces:n {#4} }
	{ \@@_parse_label_default:n {#5} }
	}
	}

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity.

[muzimuzhi]

This issue is already fixed in dev ( fixed in dev Fixed in development branch, not in stable release ).