fixes colspan width calculations, e.g. #407

lib/prawn/table.rb

@@ -552,15 +552,42 @@ def natural_column_widths
       @natural_column_widths ||=
         begin
           widths_by_column = Hash.new(0)
+
+          #calculate widths of rows without any span dummy
+          rows_with_a_span_dummy = Hash.new(false)
           cells.each do |cell|
+            rows_with_a_span_dummy[cell.row] = true if cell.is_a?(Cell::SpanDummy)
+          end
+
+          #calculate natural column width for all rows that do not include a span dummy
+          cells.each do |cell|
+            unless rows_with_a_span_dummy[cell.row]
+              widths_by_column[cell.column] = [widths_by_column[cell.column], cell.width.to_f].max
+            end
+          end
+
+          #integrate natural column widths for all rows that do include a span dummy
+          cells.each do |cell|
+            next unless rows_with_a_span_dummy[cell.row]
+            #the width of a SpanDummy cell will be calculated by the "mother" cell
             next if cell.is_a?(Cell::SpanDummy)
 
-            # Split the width of colspanned cells evenly by columns
-            width_per_column = cell.width.to_f / cell.colspan
-            cell.colspan.times do |i|
-              widths_by_column[cell.column + i] =
-                [widths_by_column[cell.column + i], width_per_column].max
+            if cell.colspan == 1
+              widths_by_column[cell.column] = [widths_by_column[cell.column], cell.width.to_f].max
+            else
+              #calculate the current with of all cells that will be spanned by the current cell
+              current_width_of_spanned_cells = widths_by_column.to_a[cell.column..(cell.column + cell.colspan - 1)].collect{|key, value| value}.inject(0, :+)
+              #update the Hash only if the new with is at least equal to the old one
+              if cell.width.to_f > current_width_of_spanned_cells
+                # Split the width of colspanned cells evenly by columns
+                width_per_column = cell.width.to_f / cell.colspan
+                # Update the Hash
+                cell.colspan.times do |i|
+                  widths_by_column[cell.column + i] = width_per_column
+                end
+              end
             end
+
           end
           widths_by_column.sort_by { |col, _| col }.map { |_, w| w }
         end

spec/table_spec.rb

@@ -91,15 +91,35 @@
       pdf = Prawn::Document.new
       first = {:content=>"Foooo fo foooooo",:width=>50,:align=>:center}
       second = {:content=>"Foooo",:colspan=>2,:width=>70,:align=>:center}
-      third = {:content=>"fooooooooooo, fooooooooooooo, fooo, foooooo fooooo",:width=>55,:align=>:center}
-      fourth = {:content=>"Bar",:width=>15,:align=>:center}
+      third = {:content=>"fooooooooooo, fooooooooooooo, fooo, foooooo fooooo",:width=>50,:align=>:center}
+      fourth = {:content=>"Bar",:width=>20,:align=>:center}
       table_content = [[
       first,
       [[second],[third,fourth]]
       ]]
       pdf.move_down(20)
+      table = Prawn::Table.new table_content, pdf
       pdf.table(table_content)
     end
+
+    #https://github.com/prawnpdf/prawn/issues/407#issuecomment-28556698
+    it "correctly computes column widths with empty cells + colspan" do
+      data = [['', ''],
+              [{:content => '', :colspan => 2}]
+              ]
+      pdf = Prawn::Document.new
+      table = Prawn::Table.new data, pdf, :column_widths => [50, 200]
+      table.column_widths.should == [50.0, 200.0]
+    end
+
+    it "illustrates a variant of problem in issue #407 - comment 28556698" do 
+      pdf = Prawn::Document.new
+      table_data = [["a", "b", "c"], [{:content=>"d", :colspan=>3}]]
+      column_widths = [50, 60, 400]
+      pdf.table(table_data, 
+        :column_widths => column_widths
+      )
+    end
   end
 
   describe "#initialize" do