Fix links that have been improperly cast to hashes.

Fixes #1784

.rubocop_todo.yml

@@ -37,6 +37,7 @@ Metrics/ClassLength:
   Exclude:
     - 'lib/blacklight/configuration.rb'
     - 'lib/blacklight/search_builder.rb'
+    - 'lib/blacklight/search_state.rb'
 
 # Offense count: 20
 Metrics/CyclomaticComplexity:

lib/blacklight/search_state.rb

@@ -114,7 +114,15 @@ def remove_facet_params(field, item)
       # from the session will get remove in the show view...
       p[:f] = (p[:f] || {}).dup
       p[:f][url_field] = (p[:f][url_field] || []).dup
-      p[:f][url_field] = p[:f][url_field] - [value]
+
+      collection = p[:f][url_field]
+      # collection should be an array, because we link to ?f[key][]=value,
+      # however, Facebook (and maybe some other PHP tools) tranform that parameters
+      # into ?f[key][0]=value, which Rails interprets as a Hash.
+      if collection.is_a? Hash
+        collection = collection.values
+      end
+      p[:f][url_field] = collection - [value]
       p[:f].delete(url_field) if p[:f][url_field].empty?
       p.delete(:f) if p[:f].empty?
       p

spec/lib/blacklight/search_state_spec.rb

@@ -266,6 +266,17 @@
       end
     end
 
+    context "when the facet_params is a HWIA" do
+      let(:facet_values) { { '0' => 'some_value', '1' => 'another_value' }.with_indifferent_access }
+      let(:facet_params) { { 'some_field' => facet_values } }
+
+      it "removes the facet / value tuple from the query parameters" do
+        params = search_state.remove_facet_params('some_field', 'some_value')
+        expect(params[:f]['some_field']).not_to include 'some_value'
+        expect(params[:f]['some_field']).to include 'another_value'
+      end
+    end
+
     context "when the facet has configuration" do
       before do
         allow(search_state).to receive(:facet_configuration_for_field).with('some_field').and_return(