Remove facets with no items from the API response

This brings the API response in line with the GUI response

app/controllers/concerns/blacklight/facet.rb

@@ -16,10 +16,13 @@ def facet_paginator(field_config, response_data)
       )
     end
 
+    # @param fields [Array<String>] a list of facet field names
+    # @return [Array<Solr::Response::Facets::FacetField>]
     def facets_from_request(fields = facet_field_names)
       fields.map { |field| facet_by_field_name(field) }.compact
     end
 
+    # @return [Array<String>] a list of the facet field names from the configuration
     def facet_field_names
       blacklight_config.facet_fields.values.map(&:field)
     end

app/presenters/blacklight/json_presenter.rb

@@ -4,7 +4,8 @@ class JsonPresenter
     include Blacklight::Facet
 
     # @param [Solr::Response] response raw solr response.
-    # @param [Array] facets list of facets
+    # @param [Array<Solr::Response::Facets::FacetField>] facets list of facets
+    # @param [Configuration] blacklight_config the configuration
     def initialize(response, facets, blacklight_config)
       @response = response
       @facets = facets
@@ -18,14 +19,17 @@ def documents
     end
 
     def search_facets_as_json
-      @facets.as_json.each do |f|
+      @facets.map do |display_facet|
+        next if display_facet.items.empty?
+        f = display_facet.as_json
         f.stringify_keys!
         f.delete "options"
         f["label"] = facet_configuration_for_field(f["name"]).label
         f["items"] = f["items"].as_json.each do |i|
           i['label'] ||= i['value']
         end
-      end
+        f
+      end.compact
     end
 
     # extract the pagination info from the response object

app/views/catalog/show.json.jbuilder

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 json.links do
   json.self polymorphic_url(@document)
 end

spec/presenters/blacklight/json_presenter_spec.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+require 'spec_helper'
+
+RSpec.describe Blacklight::JsonPresenter, api: true do
+  let(:response) { instance_double(Blacklight::Solr::Response, documents: docs, prev_page: nil, next_page: 2, total_pages: 3) }
+  let(:docs) do
+     [
+       SolrDocument.new(id: '123', title_tsim: 'Book1', author_tsim: 'Julie'),
+       SolrDocument.new(id: '456', title_tsim: 'Book2', author_tsim: 'Rosie')
+     ]
+  end
+
+  let(:facets) do
+    [
+      Blacklight::Solr::Response::Facets::FacetField.new("format_si", [{ label: "Book", value: 'Book', hits: 20 }])
+    ]
+  end
+
+  let(:config) do
+    Blacklight::Configuration.new do |config|
+      config.add_facet_field 'format', field: 'format_si', label: 'Format'
+      config.add_index_field 'title_tsim', label: 'Title:'
+    end
+  end
+
+  let(:presenter) { described_class.new(response, facets, config) }
+
+
+  describe '#search_facets_as_json' do
+    subject { presenter.search_facets_as_json }
+
+    context 'for defined facets that are present in the response' do
+      it 'has a label' do
+        expect(subject.first["label"]).to eq 'Format'
+      end
+    end
+
+
+    context 'when there are defined facets that are not in the response' do
+      before do
+        config.add_facet_field 'example_query_facet_field', label: 'Publish Date', query: {}
+      end
+
+      let(:facets) do
+        [
+          Blacklight::Solr::Response::Facets::FacetField.new("format_si", [{ label: "Book", value: 'Book', hits: 20 }]),
+          Blacklight::Solr::Response::Facets::FacetField.new("example_query_facet_field", [])
+        ]
+      end
+
+      it 'shows only facets that are defined' do
+        expect(subject.map { |f| f['name'] }).to eq ['format_si']
+      end
+    end
+  end
+end