resolves #1737 add backlink from bibref on bibliography entry to firs…

…t reference to that entry in the document (PR #2221)

CHANGELOG.adoc

@@ -11,6 +11,7 @@ Enhancements::
 
 * add `save_theme` helper to work with a copy of the theme within a scope (#2196)
 * add support for `scale` attribute or `iw` unit on `pdfwidth` attribute on image macros (#1933)
+* add backlink from bibref on bibliography entry to first reference to that entry in the document (#1737)
 
 == 2.0.7 (2022-06-03) - @mojavelinux
 

lib/asciidoctor/pdf/converter.rb

@@ -404,6 +404,7 @@ def init_pdf doc
         @list_bullets = []
         @bottom_gutters = [{}]
         @rendered_footnotes = []
+        @bibref_refs = ::Set.new
         @conum_glyphs = ConumSets[@theme.conum_glyphs || 'circled'] || (@theme.conum_glyphs.split ',').map do |r|
           from, to = r.lstrip.split '-', 2
           to ? ((get_char from)..(get_char to)).to_a : [(get_char from)]
@@ -2393,20 +2394,25 @@ def convert_inline_anchor node
               if (text = ref.xreftext node.attr 'xrefstyle', nil, true)&.include? '<a'
                 text = text.gsub DropAnchorRx, ''
               end
+              if ref.inline? && ref.type == :bibref && !scratch? && (@bibref_refs.add? refid)
+                anchor = %(<a id="_bibref_ref_#{refid}">#{DummyText}</a>)
+              end
               @resolving_xref = nil
             end
-            %(<a anchor="#{derive_anchor_from_id refid}">#{text || "[#{refid}]"}</a>).gsub ']', '&#93;'
+            %(#{anchor || ''}<a anchor="#{derive_anchor_from_id refid}">#{text || "[#{refid}]"}</a>).gsub ']', '&#93;'
           else
             %(<a anchor="#{doc.attr 'pdf-anchor'}">#{node.text || '[^top&#93;'}</a>)
           end
         when :ref
           # NOTE: destination is created inside callback registered by FormattedTextTransform#build_fragment
           %(<a id="#{node.id}">#{DummyText}</a>)
         when :bibref
-          # NOTE: destination is created inside callback registered by FormattedTextTransform#build_fragment
+          id = node.id
           # NOTE: technically node.text should be node.reftext, but subs have already been applied to text
-          reftext = (reftext = node.reftext) ? %([#{reftext}]) : %([#{node.id}])
-          %(<a id="#{node.id}">#{DummyText}</a>#{reftext})
+          reftext = (reftext = node.reftext) ? %([#{reftext}]) : %([#{id}])
+          reftext = %(<a anchor="_bibref_ref_#{id}">#{reftext}</a>) if @bibref_refs.include? id
+          # NOTE: destination is created inside callback registered by FormattedTextTransform#build_fragment
+          %(<a id="#{id}">#{DummyText}</a>#{reftext})
         else
           log :warn, %(unknown anchor type: #{node.type.inspect})
           nil

spec/list_spec.rb

@@ -2112,5 +2112,32 @@
       (expect lines).to include 'The recommended reading includes [1].'
       (expect lines).to include '▪ [1] Bar, Foo. All The Things. 2010.'
     end
+
+    it 'should create bidirectional links between first bibref reference and entry' do
+      pdf = to_pdf <<~'EOS'
+      The recommended reading includes <<bar>>.
+
+      Did you read <<bar>>?
+
+      <<<
+
+      [bibliography]
+      == Bibliography
+
+      * [[[bar]]] Bar, Foo. All The Things. 2010.
+      * [[[baz]]] Baz. The Rest of the Story. 2020.
+      EOS
+
+      forward_refs = get_annotations pdf, 1
+      (expect forward_refs).to have_size 2
+      (expect forward_refs.map {|it| it[:Dest] }.uniq).to eql %w(bar)
+      ids = (get_names pdf).keys
+      (expect ids).to include '_bibref_ref_bar'
+      (expect ids).to include 'bar'
+      (expect ids).to include 'baz'
+      back_refs = get_annotations pdf, 2
+      (expect back_refs).to have_size 1
+      (expect back_refs[0][:Dest]).to eql '_bibref_ref_bar'
+    end
   end
 end