resolves asciidoctor#2480 ensure indentation is preserved at page tra…

…nsition of index when media=prepress

CHANGELOG.adoc

@@ -40,6 +40,7 @@ Improvements::
 
 Bug Fixes::
 
+* ensure indentation is preserved at page transition of index when media=prepress; prevents margin from shifting to the left (#2480)
 * correctly map all icons from FontAwesome 4 (#2373)
 * resolve remote image in document title or section title with autogenerated ID
 * keep caret between items in menu macro with previous item if items wrap

lib/asciidoctor/pdf/ext/prawn/document/column_box.rb

@@ -15,8 +15,11 @@ def move_past_bottom
     initial_margins = doc.page.margins
     parent_.move_past_bottom
     if doc.page.margins != initial_margins
-      doc.bounds = self.class.new doc, parent_, [(margin_box = doc.margin_box).absolute_left, @y],
+      doc.bounds = bounds = self.class.new doc, parent_, [(margin_box = doc.margin_box).absolute_left, @y],
         columns: @columns, reflow_margins: @reflow_margins, spacer: @spacer, width: margin_box.width, height: @height
+      # ensure indentation is preserved across page break
+      bounds.add_left_padding @total_left_padding if @total_left_padding > 0
+      bounds.add_right_padding @total_right_padding if @total_right_padding > 0
     end
     nil
   end

spec/index_spec.rb

@@ -945,6 +945,63 @@
     (expect s_category_text[:x]).to eql 36.0
   end
 
+  # this happens if the term sits right on the page boundary and the hanging indent is still active
+  it 'should preserve indentation when recreating column box on subsequent pages' do
+    pdf_theme = {
+      page_margin: 54,
+      page_margin_inner: 72,
+      page_margin_outer: 36,
+    }
+    pdf = to_pdf <<~'END', pdf_theme: pdf_theme, analyze: true
+    = Document Title
+    :doctype: book
+    :media: prepress
+    :notitle:
+    :pdf-page-size: A5
+
+    == Chapter
+
+    ((foo)) and ((bar))
+
+    ((yin)) and ((yang))
+
+    ((tea)) and ((coffee))
+
+    ((left)) and ((right))
+
+    ((salt)) and ((pepper))
+
+    ((up)) and ((down))
+
+    ((sugar)) and ((spice))
+
+    ((day)) and ((night))
+
+    ((melody)) and ((harmony))
+
+    ((inside)) and ((outside))
+
+    ((forward)) and ((back))
+
+    ((cake)) and ((icing))
+
+    ((to)) and ((fro))
+
+    ((apples)) and ((oranges))
+
+    ((over)) and ((under))
+
+    ((light)) and ((dark))
+
+    [index]
+    == Index
+    END
+
+    u_category_text = pdf.find_unique_text 'U', page_number: 4
+    (expect u_category_text).not_to be_nil
+    (expect u_category_text[:x]).to eql 36.0
+  end
+
   it 'should preserve column count on subsequent pages' do
     pdf_theme = {
       page_margin: 36,