Linter Rule: Allow one herb:slots directive per template

Rule: herb-slots-single-directive

Description

Flags every herb:slots directive after the first one in a template.

Rationale

The engine reads only the first herb:slots directive in a template, so any later one does nothing, silently. The dangerous shape is a template that already opts into one mode near the top gaining a second directive with the other mode further down, where the author believes they switched modes and the engine never noticed. The offense names the directive that wins and its line, so the fix is one deletion.

The mode tokens themselves are validated by herb-slots-valid-mode, the way herb:state splits the same concerns between herb-state-directive-syntax and herb-state-single-declaration.

Examples

✅ Good

<%# herb:slots client %>

<div><%= @title %></div>

🚫 Bad

<%# herb:slots client %>

<div><%= @title %></div>

<%# herb:slots server %>
This template already declares `herb:slots client` on line 1, and the engine reads only the first directive, so this one does nothing. Remove it, and put the mode the template should use on the first directive. (herb-slots-single-directive)

References

• herb-slots-valid-mode
• herb-state-single-declaration