Use a simple implementation of range subtract and use it with cache

Author: tompng

lib/reline/line_editor.rb

@@ -660,42 +660,9 @@ def add_dialog_proc(name, p, context = nil)
   end
 
   private def range_subtract(base_ranges, subtract_ranges)
-    points = []
-    base_ranges.each do |range|
-      points << [range.begin, 1, 1]
-      points << [range.end, -1, 1]
-    end
-    subtract_ranges.each do |range|
-      points << [range.begin, 1, -1]
-      points << [range.end, -1, -1]
-    end
-    ranges = []
-    base_count = 0
-    subtract_count = 0
-    open = false
-    points.sort.each do |point, diff, mode|
-      if mode == 1
-        base_count += diff
-      else
-        subtract_count += diff
-      end
-      next if open == (base_count > 0 && subtract_count == 0)
-      open = !open
-      if open
-        if ranges.last&.end === point
-          ranges[-1] = (ranges.last.begin...)
-        else
-          ranges << (point...)
-        end
-      else
-        if ranges.last.begin === point
-          ranges.pop
-        else
-          ranges[-1] = ranges.last.begin...point
-        end
-      end
-    end
-    ranges
+    indices = base_ranges.flat_map(&:to_a).uniq.sort - subtract_ranges.flat_map(&:to_a)
+    chunks = indices.chunk_while { |a, b| a + 1 == b }
+    chunks.map { |a| a.first...a.last + 1 }
   end
 
   private def dialog_range(dialog, dialog_y)
@@ -725,8 +692,10 @@ def add_dialog_proc(name, p, context = nil)
     end
     return if old_dialog_ranges.empty? && new_dialog_ranges.empty?
     ranges_to_restore = {}
+    subtract_cache = {}
     old_dialog_ranges.each do |y, old_x_ranges|
-      ranges = range_subtract(old_x_ranges, new_dialog_ranges[y] || [])
+      new_x_ranges = new_dialog_ranges[y] || []
+      ranges = subtract_cache[[old_x_ranges, new_x_ranges]] ||= range_subtract(old_x_ranges, new_x_ranges)
       ranges_to_restore[y] = ranges if ranges.any?
     end