backport #1833 align footnotes block to bottom of page it is placed on

7 files changed, 150 insertions, 132 deletions

diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index 1da1594a..cc34895a 100644
--- a/CHANGELOG.adoc
+++ b/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 {uri-repo}/commits/v1.6.x[commit history] on GitHub.
 
+== Unreleased
+
+Enhancements::
+
+* align footnotes block to the bottom of the page it is placed on (#1833)
+
 == 1.6.0 (2021-05-10) - @mojavelinux
 
 Enhancements::
diff --git a/examples/basic-example.pdf b/examples/basic-example.pdf
index 3ee319ce..74118970 100644
--- a/examples/basic-example.pdf
+++ b/examples/basic-example.pdf
@@ -47,7 +47,7 @@ endobj
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@@ -956,24 +956,24 @@ endobj
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 %%EOF
diff --git a/examples/chronicles-example.pdf b/examples/chronicles-example.pdf
index c6ea7f07..66e0f714 100644
--- a/examples/chronicles-example.pdf
+++ b/examples/chronicles-example.pdf
@@ -2638,7 +2638,7 @@ ET
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diff --git a/lib/asciidoctor/pdf/converter.rb b/lib/asciidoctor/pdf/converter.rb
index 5c1374dc..0eeab4a2 100644
--- a/lib/asciidoctor/pdf/converter.rb
+++ b/lib/asciidoctor/pdf/converter.rb
@@ -607,13 +607,18 @@ module Asciidoctor
       def layout_footnotes node
         return if (fns = (doc = node.document).footnotes - @footnotes).empty?
         theme_margin :footnotes, :top
-        theme_font :footnotes do
-          (title = doc.attr 'footnotes-title') && (layout_caption title, category: :footnotes)
-          item_spacing = @theme.footnotes_item_spacing || 0
-          fns.each do |fn|
-            layout_prose %(<a id="_footnotedef_#{index = fn.index}">#{DummyText}</a>[<a anchor="_footnoteref_#{index}">#{index}</a>] #{fn.text}), margin_bottom: item_spacing, hyphenate: true
+        with_dry_run do |box_height = nil|
+          if box_height && (delta = cursor - box_height) > 0
+            move_down delta
+          end
+          theme_font :footnotes do
+            (title = doc.attr 'footnotes-title') && (layout_caption title, category: :footnotes)
+            item_spacing = @theme.footnotes_item_spacing
+            fns.each do |fn|
+              layout_prose %(<a id="_footnotedef_#{index = fn.index}">#{DummyText}</a>[<a anchor="_footnoteref_#{index}">#{index}</a>] #{fn.text}), margin_bottom: item_spacing, hyphenate: true
+            end
+            @footnotes += fns unless scratch?
           end
-          @footnotes += fns
         end
         nil
       end
diff --git a/lib/asciidoctor/pdf/ext/prawn/extensions.rb b/lib/asciidoctor/pdf/ext/prawn/extensions.rb
index fc565f12..218427dd 100644
--- a/lib/asciidoctor/pdf/ext/prawn/extensions.rb
+++ b/lib/asciidoctor/pdf/ext/prawn/extensions.rb
@@ -903,6 +903,11 @@ module Asciidoctor
         [(whole_pages * full_page_height + partial_page_height), whole_pages, partial_page_height]
       end
 
+      def with_dry_run &block
+        total_height, = dry_run(&block)
+        instance_exec total_height, &block
+      end
+
       # Attempt to keep the objects generated in the block on the same page
       #
       # TODO: short-circuit nested usage
diff --git a/spec/footnote_spec.rb b/spec/footnote_spec.rb
index 462c8dc8..0a717b63 100644
--- a/spec/footnote_spec.rb
+++ b/spec/footnote_spec.rb
@@ -24,6 +24,7 @@ describe 'Asciidoctor::PDF::Converter - Footnote' do
     # footnote item
     (expect (strings.slice 6, 3).join).to eql '[1] More about that thing.'
     (expect text[6][:y]).to be < text[5][:y]
+    (expect text[6][:y]).to be < 60
     (expect text[6][:page_number]).to be 1
     (expect text[6][:font_size]).to be 8
     (expect (text.slice 6, 3).map {|it| [it[:y], it[:font_size]] }.uniq).to have_size 1
@@ -58,6 +59,7 @@ describe 'Asciidoctor::PDF::Converter - Footnote' do
     (expect strings.slice(-3, 3).join).to eql '[1] More about that thing.'
     (expect text[-1][:page_number]).to be 2
     (expect text[-1][:font_size]).to be 8
+    (expect text[-1][:y]).to be < 60
   end
 
   it 'should add title to footnotes block if footnotes-title is set' do
diff --git a/spec/reference/open-unbreakable-option-fit.pdf b/spec/reference/open-unbreakable-option-fit.pdf
index ac413af1..ec35bf30 100644
--- a/spec/reference/open-unbreakable-option-fit.pdf
+++ b/spec/reference/open-unbreakable-option-fit.pdf
@@ -4,8 +4,8 @@
 << /Title (Untitled)
 /Creator (Asciidoctor PDF 1.6.1.dev, based on Prawn 2.4.0)
 /Producer (Asciidoctor PDF 1.6.1.dev, based on Prawn 2.4.0)
-/ModDate (D:20210904153834-06'00')
-/CreationDate (D:20210904153834-06'00')
+/ModDate (D:20210904154011-06'00')
+/CreationDate (D:20210904154011-06'00')
 >>
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@@ -393,7 +393,7 @@ endobj
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+<< /Length 6683
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