resolves asciidoctor#1737 add backlink from bibref to first reference…

… to that entry in the document

CHANGELOG.adoc

@@ -5,6 +5,12 @@
 This document provides a high-level view of the changes to the {project-name} by release.
 For a detailed view of what has changed, refer to the {url-repo}/commits/main[commit history] on GitHub.
 
+== Unreleased
+
+Enhancements::
+
+* add backlink from bibref to first reference to that entry in the document (#1737)
+
 == 2.0.6 (2022-05-30) - @mojavelinux
 
 Bug Fixes::

lib/asciidoctor/pdf/converter.rb

@@ -400,6 +400,7 @@ 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)]
@@ -2373,20 +2374,23 @@ def convert_inline_anchor node
               if (text = ref.xreftext node.attr 'xrefstyle', nil, true)&.include? '<a'
                 text = text.gsub DropAnchorRx, ''
               end
+              backref = %(<a id="_bibref_ref_#{refid}">#{DummyText}</a>) if ref.inline? && ref.type == :bibref && (@bibref_refs.add? refid)
               @resolving_xref = nil
             end
-            %(<a anchor="#{derive_anchor_from_id refid}">#{text || "[#{refid}]"}</a>).gsub ']', '&#93;'
+            %(#{backref || ''}<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 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