[mattboldt]

Hello! Another one from setting up ReActionView on my app (the first was marcoroth/herb#2778). Same disclosure as last time: I leaned on Claude for a lot of the digging here.

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With config.slots = true, Slots::Resolver is prepended to the view paths and rebuilds every HTML template with the :slots format. It answers any lookup whose formats include :slots. Once the MIME type is registered, a lookup with default formats lists every registered format, :slots among them, so the prepended resolver wins and the render returns the values Hash where the caller expected markup.

# config.slots = true
lookup = ActionView::LookupContext.new(ActionController::Base.view_paths)
lookup.formats.first(3)  # => [:html, :text, :js]

lookup.find_template("shared/record_search_input", [], true, [:builder]).format
# => :slots

In our app this showed up as about 31 no implicit conversion of Hash into String errors from renders that aren't pinned to [:html]: ActionView::TestCase view tests, ViewComponent tests, and template.render inside simple_form inputs.

This makes the resolver return nothing unless :slots is the first requested format. A slots request still resolves as before, and everything else falls through to the resolvers Rails built.

Tested with test/slots/resolver_test.rb, which gets a case for a lookup that lists :slots after :html, and bundle exec rake test on this branch rebased onto current main (234 runs, 0 failures, 3 skips). We've been running it as a local patch on 0.6.0: the lookup above returns :html, a [:slots] lookup still returns :slots, and all 31 of those errors go away.