Re-implement prev_spaces feature for pasted code

Author: tompng

lib/irb/ruby-lex.rb

@@ -356,6 +356,16 @@ def free_indent_token?(token)
     %i[on_tstring_beg on_backtick on_regexp_beg on_symbeg].include?(token.event)
   end
 
+  def indent_difference(lines, line_results, open_token)
+    return 0 unless open_token
+    line_index = open_token.pos[0] - 1
+    _tokens, prev_opens, _next_opens, min_depth = line_results[line_index]
+    indent_level, _nesting_level = calc_nesting_depth(prev_opens.take(min_depth))
+    calculated_indent = 2 * indent_level
+    actual_indent = lines[line_index][/^ */].size
+    actual_indent - calculated_indent
+  end
+
   def process_indent_level(tokens, lines, line_index, is_newline)
     line_results = IRB::NestingParser.parse_by_line(tokens)
     result = line_results[line_index]
@@ -374,10 +384,16 @@ def process_indent_level(tokens, lines, line_index, is_newline)
 
     preserve_indent = lines[line_index - (is_newline ? 1 : 0)][/^ */].size
 
+    # Calculates base indent for pasted code
+    # irb(main):001:1*     if 1 # Base indent is 4
+    # irb(main):002:1*       2
+    # irb(main):003:0>     end
+    base_indent = [0, indent_difference(lines, line_results, prev_opens.last)].max
+
     if free_indent_token?(prev_opens.last)
       if is_newline && prev_opens.last.pos[0] == line_index
         # First newline inside free-indent token
-        indent
+        base_indent + indent
       else
         # Accept any number of indent inside free-indent token
         preserve_indent
@@ -395,21 +411,21 @@ def process_indent_level(tokens, lines, line_index, is_newline)
       if prev_opens.size < next_opens.size || prev_opens.last == next_opens.last
         if is_newline && lines[line_index].empty? && line_results[line_index - 1][1].last != prev_opens.last
           # First line in heredoc
-          indent
+          tok.match?(/^<<[-~]/) ? base_indent + indent : indent
         elsif tok.match?(/^<<~/)
           # Accept extra indent spaces inside `<<~` heredoc
-          [indent, preserve_indent].max
+          [base_indent + indent, preserve_indent].max
         else
           # Accept any number of indent inside other heredoc
           preserve_indent
         end
       else
         # Heredoc close
         prev_line_indent_level, _prev_line_nesting_level = calc_nesting_depth(prev_opens)
-        tok.match?(/^<<[~-]/) ? 2 * (prev_line_indent_level - 1) : 0
+        tok.match?(/^<<[~-]/) ? base_indent + 2 * (prev_line_indent_level - 1) : 0
       end
     else
-      indent
+      base_indent + indent
     end
   end