erb.rb: preserve the behavior for invalid syntax

comment. Fix regression at r58948.

I even don't want to deprecate it because deprecation needs to lex all
embedded Ruby script using Ripper and it would be slow.  So Let me just
keep this behavior of Ruby 2.4. No change is the best compatibility.

This commit stopped using String#-@ because it's harmful for "ambiguous
first argument" warning if we really want to maintain this behavior.

[Bug #14243]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61497 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/erb.rb

@@ -291,7 +291,7 @@ class ERB
   # <i>Generates</i>:
   #
   #   #coding:UTF-8
-  #   _erbout=+''; _erbout.<<(-"Got "); _erbout.<<(( obj ).to_s); _erbout.<<(-"!\n"); _erbout
+  #   _erbout=+''; _erbout.<< "Got ".freeze; _erbout.<<(( obj ).to_s); _erbout.<< "!\n".freeze; _erbout
   #
   # By default the output is sent to the print method.  For example:
   #
@@ -302,7 +302,7 @@ class ERB
   # <i>Generates</i>:
   #
   #   #coding:UTF-8
-  #   print(-"Got "); print(( obj ).to_s); print(-"!\n")
+  #   print "Got ".freeze; print(( obj ).to_s); print "!\n".freeze
   #
   # == Evaluation
   #
@@ -576,17 +576,8 @@ class ERB
       end
     end
 
-    def content_dump(s) # :nodoc:
-      n = s.count("\n")
-      if n > 0
-        s.dump << "\n" * n
-      else
-        s.dump
-      end
-    end
-
     def add_put_cmd(out, content)
-      out.push("#{@put_cmd}(-#{content_dump(content)})")
+      out.push("#{@put_cmd} #{content.dump}.freeze#{"\n" * content.count("\n")}")
     end
 
     def add_insert_cmd(out, content)
@@ -668,7 +659,7 @@ class ERB
       when '<%='
         add_insert_cmd(out, content)
       when '<%#'
-        # out.push("# #{content_dump(content)}")
+        # commented out
       end
     end
 

test/erb/test_erb.rb

@@ -622,6 +622,13 @@ EOS
     erb = @erb.new("<%= 1 %>")
     assert_raise(TypeError) { erb.result_with_hash({ 1 => "1" }) }
   end
+
+  # Bug#14243
+  def test_half_working_comment_backward_compatibility
+    assert_nothing_raised do
+      @erb.new("<% # comment %>\n").result
+    end
+  end
 end
 
 class TestERBCoreWOStrScan < TestERBCore