erb.rb: increase warn level only when non-zero safe_level

is given.

This is merging Eric's patch in [Bug #15479] to Ruby 2.6's behavior in r66631.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66632 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/erb.rb

@@ -814,7 +814,7 @@ class ERB
   def initialize(str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eoutvar=NOT_GIVEN, trim_mode: nil, eoutvar: '_erbout')
     # Complex initializer for $SAFE deprecation at [Feature #14256]. Use keyword arguments to pass trim_mode or eoutvar.
     if safe_level != NOT_GIVEN
-      warn 'Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.', uplevel: 1 if $VERBOSE
+      warn 'Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.', uplevel: 1 if $VERBOSE || !ZERO_SAFE_LEVELS.include?(safe_level)
     else
       safe_level = nil
     end
@@ -836,6 +836,8 @@ class ERB
   end
   NOT_GIVEN = Object.new
   private_constant :NOT_GIVEN
+  ZERO_SAFE_LEVELS = [0, nil]
+  private_constant :ZERO_SAFE_LEVELS
 
   ##
   # Creates a new compiler for ERB.  See ERB::Compiler.new for details

test/erb/test_erb.rb

@@ -663,12 +663,18 @@ EOS
 
   # [deprecated] These interfaces will be removed later
   def test_deprecated_interface_warnings
-    [nil, 0, 1, 2].each do |safe|
+    [nil, 0].each do |safe|
       assert_warning(/2nd argument of ERB.new is deprecated/) do
         ERB.new('', safe)
       end
     end
 
+    [1, 2].each do |safe|
+      assert_warn(/2nd argument of ERB.new is deprecated/) do
+        ERB.new('', safe)
+      end
+    end
+
     [nil, '', '%', '%<>'].each do |trim|
       assert_warning(/3rd argument of ERB.new is deprecated/) do
         ERB.new('', nil, trim)