erb.rb: frozen-string-literal safe

* lib/erb.rb (ERB#set_eoutvar): explicitly make mutable string as
  a buffer to make ERB work with --enable-frozen-string-literal.
  [ruby-core:73561] [Bug #12031]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53682 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 18 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 06e25a7ecd..73371bc898 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Jan 29 11:13:33 2016  Jeremy Evans  <code@jeremyevans.net>
+
+	* lib/erb.rb (ERB#set_eoutvar): explicitly make mutable string as
+	  a buffer to make ERB work with --enable-frozen-string-literal.
+	  [ruby-core:73561] [Bug #12031]
+
 Fri Jan 29 10:44:56 2016  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
 
 	* lib/net/http/header.rb: Warn nil variable on HTTP Header.
diff --git a/lib/erb.rb b/lib/erb.rb
index 5223a280ad..2e9fad98b4 100644
--- a/lib/erb.rb
+++ b/lib/erb.rb
@@ -280,7 +280,7 @@ class ERB
   # ERB#src:
   #
   #   compiler = ERB::Compiler.new('<>')
-  #   compiler.pre_cmd    = ["_erbout=''"]
+  #   compiler.pre_cmd    = ["_erbout=String.new"]
   #   compiler.put_cmd    = "_erbout.concat"
   #   compiler.insert_cmd = "_erbout.concat"
   #   compiler.post_cmd   = ["_erbout"]
@@ -291,7 +291,7 @@ class ERB
   # <i>Generates</i>:
   #
   #   #coding:UTF-8
-  #   _erbout=''; _erbout.concat "Got "; _erbout.concat(( obj ).to_s); _erbout.concat "!\n"; _erbout
+  #   _erbout=String.new; _erbout.concat "Got "; _erbout.concat(( obj ).to_s); _erbout.concat "!\n"; _erbout
   #
   # By default the output is sent to the print method.  For example:
   #
@@ -860,7 +860,7 @@ class ERB
   def set_eoutvar(compiler, eoutvar = '_erbout')
     compiler.put_cmd = "#{eoutvar}.concat"
     compiler.insert_cmd = "#{eoutvar}.concat"
-    compiler.pre_cmd = ["#{eoutvar} = ''"]
+    compiler.pre_cmd = ["#{eoutvar} = String.new"]
     compiler.post_cmd = ["#{eoutvar}.force_encoding(__ENCODING__)"]
   end
 
diff --git a/test/erb/test_erb.rb b/test/erb/test_erb.rb
index 29fbf97686..97f45af73d 100644
--- a/test/erb/test_erb.rb
+++ b/test/erb/test_erb.rb
@@ -534,6 +534,15 @@ EOS
     EOS
     assert_equal(ans, extended_erb.new(src).result)
   end
+
+  def test_frozen_string_literal
+    bug12031 = '[ruby-core:73561] [Bug #12031]'
+    e = @erb.new("<%#encoding: us-ascii%>a")
+    e.src.sub!(/\A#(?:-\*-)?(.*)(?:-\*-)?/) {
+      '# -*- \1; frozen-string-literal: true -*-'
+    }
+    assert_equal("a", e.result, bug12031)
+  end
 end
 
 class TestERBCoreWOStrScan < TestERBCore