Allow style paths relative to Jekyll's source directory (#180)

* Use site source path to qualify style location

* Fix tests by checking for existence of local style

* Add test that fails in master and succeeds in this branch

features/bibtex.feature

@@ -369,3 +369,49 @@ Feature: BibTeX
     Then the _site directory should exist
     And the "_site/scholar.html" file should exist
     And I should not see "{%[\w*]raw[\w*]%}" in "_site/scholar.html"
+
+  @config @bibliography @style
+  Scenario: A custom style with Jekyll source directory set
+    Given I have a configuration file with:
+      | key     | value              |
+      | source  | src                |
+    And I have a scholar configuration with:
+      | key     | value              |
+      | source  | _bibliography      |
+      | style   | _styles/custom.csl |
+    And I have a "src" directory
+    And I have a "src/_bibliography" directory
+    And I have a "src/_styles" directory
+    And I have a file "src/_styles/custom.csl":
+      """
+      <style>
+        <citation>
+          <layout>
+            <text variable="title"/>
+          </layout>
+        </citation>
+        <bibliography>
+          <layout>
+            <text variable="title"/>
+          </layout>
+        </bibliography>
+      </style>
+      """
+    And I have a file "src/_bibliography/references.bib":
+      """
+      @book{ruby,
+        title     = {The Ruby Programming Language},
+        author    = {Flanagan, David and Matsumoto, Yukihiro},
+        year      = {2008},
+        publisher = {O'Reilly Media}
+      }
+      """
+    And I have a page "src/scholar.html":
+      """
+      ---
+      ---
+      {% bibliography --style _styles/custom.csl %}
+      """
+    When I run jekyll
+    Then the _site directory should exist
+    And I should see "The Ruby Programming Language" in "_site/scholar.html"
\ No newline at end of file

lib/jekyll/scholar/utilities.rb

@@ -598,12 +598,12 @@ module Jekyll
           item.label = label unless label.nil?
 
           item
-        }, STYLES[style].citation
+        }, style_cache(style).citation
       end
 
       def render_bibliography(entry, index = nil)
         renderer.render citation_item_for(entry, index),
-          STYLES[style].bibliography
+          style_cache(style).bibliography
       end
 
       def citation_item_for(entry, citation_number = nil)
@@ -693,6 +693,25 @@ module Jekyll
         config.merge!(site.config['scholar'] || {})
         self
       end
+
+      # Try to resolve local style paths
+      # relative to Jekyll's source directory
+      def style_cache(style_name)
+        style =
+          if site && site.source
+            site_relative_style = File.join(site.source, style_name)
+
+            if Pathname.new(style_name).relative? && File.exist?(site_relative_style)
+              site_relative_style
+            else
+              style_name
+            end
+          else
+            style_name
+          end
+
+        STYLES[style]
+      end
     end
 
   end