Add support for dynamic field configuration for index, show and facet

fields, allowing configurations like:

```ruby
config.add_facet_field '*_facet'
config.add_show_field '*_display'
config.add_index_field 'title_*'
```

lib/blacklight/configuration/fields.rb

@@ -75,11 +75,29 @@ def add_solr_field config_key, *args, &block
             field_config_from_key_and_hash(config_key, *args)
           when Array
             field_config_from_array(config_key, *args)
+            return # we've iterated over the array above.
           else
             field_config_from_field_or_hash(config_key, *args)
         end
 
-        return if field_config.is_a? Array
+        # look up any dynamic fields
+        if field_config.field.to_s =~ /\*/ and luke_fields
+          salient_fields = luke_fields.select do |k,v| 
+            k =~ Regexp.new("^" + field_config.field.to_s.gsub('*', '.+') + "$")
+          end
+
+          salient_fields.each do |field, luke_config|
+            config = field_config.dup
+            config.field = field
+            if self[config_key.pluralize][ config.field ]
+              self[config_key.pluralize][ config.field ] = config.merge(self[config_key.pluralize][ config.field ])
+            else
+              add_solr_field(config_key, config)
+            end
+          end
+
+          return
+        end
 
         if block_given?
           yield field_config
@@ -94,6 +112,22 @@ def add_solr_field config_key, *args, &block
       end
 
       protected
+      def luke_fields
+        if @table[:luke_fields] === false
+          return nil
+        end
+
+        @table[:luke_fields] ||= begin
+          if has_key? :blacklight_solr
+            blacklight_solr.get('admin/luke', params: { fl: '*', 'json.nl' => 'map' })['fields']
+          end
+        rescue
+          false
+        end
+
+        @table[:luke_fields] || nil
+      end
+
       # Add a solr field by a solr field name and hash 
       def field_config_from_key_and_hash config_key, solr_field, field_or_hash = {}
         field_config = field_config_from_field_or_hash(config_key, field_or_hash)

spec/lib/blacklight/configuration_spec.rb

@@ -167,7 +167,18 @@
     it "should raise on nil solr field name" do
       expect { @config.add_facet_field(nil) }.to raise_error ArgumentError
     end
-
+
+    it "should take wild-carded field names and dereference them to solr fields" do
+      @config.stub(luke_fields: { 
+        "some_field_facet" => {}, 
+        "another_field_facet" => {},
+        "a_facet_field" => {},
+        })
+      @config.add_index_field "*_facet"
+
+      expect(@config.index_fields.keys).to eq ["some_field_facet", "another_field_facet"]
+    end
+
   end
 
   describe "add_index_field" do
@@ -201,6 +212,17 @@
       expect { @config.add_index_field(nil) }.to raise_error ArgumentError
     end
 
+    it "should take wild-carded field names and dereference them to solr fields" do
+      @config.stub(luke_fields: { 
+        "some_field_display" => {}, 
+        "another_field_display" => {},
+        "a_facet_field" => {},
+        })
+      @config.add_index_field "*_display"
+
+      expect(@config.index_fields.keys).to eq ["some_field_display", "another_field_display"]
+    end
+
   end
 
   describe "add_show_field" do
@@ -235,6 +257,17 @@
       expect { @config.add_show_field(nil) }.to raise_error ArgumentError
     end
 
+    it "should take wild-carded field names and dereference them to solr fields" do
+      @config.stub(luke_fields: { 
+        "some_field_display" => {}, 
+        "another_field_display" => {},
+        "a_facet_field" => {},
+        })
+      @config.add_show_field "*_display"
+
+      expect(@config.show_fields.keys).to eq ["some_field_display", "another_field_display"]
+    end
+
   end