fixes colspan width calculations, e.g. #407

lib/prawn/table.rb

@@ -6,13 +6,14 @@
 #
 # This is free software. Please see the LICENSE and COPYING files for details.
 
-require 'prawn/table/cells'
-require 'prawn/table/cell'
-require 'prawn/table/cell/in_table'
-require 'prawn/table/cell/text'
-require 'prawn/table/cell/subtable'
-require 'prawn/table/cell/image'
-require 'prawn/table/cell/span_dummy'
+require_relative 'table/column_width_calculator'
+require_relative 'table/cells'
+require_relative 'table/cell'
+require_relative 'table/cell/in_table'
+require_relative 'table/cell/text'
+require_relative 'table/cell/subtable'
+require_relative 'table/cell/image'
+require_relative 'table/cell/span_dummy'
 
 module Prawn
 
@@ -549,21 +550,7 @@ def assert_proper_table_data(data)
     # Returns an array of each column's natural (unconstrained) width.
     #
     def natural_column_widths
-      @natural_column_widths ||=
-        begin
-          widths_by_column = Hash.new(0)
-          cells.each do |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
-            end
-          end
-          widths_by_column.sort_by { |col, _| col }.map { |_, w| w }
-        end
+      @natural_column_widths ||= ColumnWidthCalculator.new(cells).natural_widths
     end
 
     # Returns the "natural" (unconstrained) width of the table. This may be

lib/prawn/table/column_width_calculator.rb

@@ -0,0 +1,55 @@
+module Prawn
+  class Table
+    class ColumnWidthCalculator
+      def initialize(cells)
+        @cells = cells
+
+        @widths_by_column        = Hash.new(0)
+        @rows_with_a_span_dummy  = Hash.new(false)
+      end
+
+      def natural_widths
+        @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)
+
+          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
+    end
+  end
+end

spec/table_spec.rb

@@ -91,15 +91,36 @@
       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]
+
+      # Before we fixed #407, this line incorrectly raise a CannotFit error
+      pdf.table(table_data, :column_widths => column_widths)
+    end
   end
 
   describe "#initialize" do