[ruby/psych] Raise specific error when aliases are not enabled

https://github.com/ruby/psych/commit/0c11ddcf46

3 files changed, 9 insertions, 2 deletions

diff --git a/ext/psych/lib/psych.rb b/ext/psych/lib/psych.rb
index 42d79efb83..4a2ab58514 100644
--- a/ext/psych/lib/psych.rb
+++ b/ext/psych/lib/psych.rb
@@ -307,7 +307,7 @@ module Psych
   # A Psych::DisallowedClass exception will be raised if the yaml contains a
   # class that isn't in the +permitted_classes+ list.
   #
-  # A Psych::BadAlias exception will be raised if the yaml contains aliases
+  # A Psych::AliasesNotEnabled exception will be raised if the yaml contains aliases
   # but the +aliases+ keyword argument is set to false.
   #
   # +filename+ will be used in the exception message if any exception is raised
diff --git a/ext/psych/lib/psych/exception.rb b/ext/psych/lib/psych/exception.rb
index f473b95a3b..04a9a906a4 100644
--- a/ext/psych/lib/psych/exception.rb
+++ b/ext/psych/lib/psych/exception.rb
@@ -6,6 +6,13 @@ module Psych
   class BadAlias < Exception
   end
 
+  # Subclasses `BadAlias` for backwards compatibility
+  class AliasesNotEnabled < BadAlias
+    def initialize
+      super "Alias parsing was not enabled. To enable it, pass `aliases: true` to `Psych::load` or `Psych::safe_load`."
+    end
+  end
+
   class DisallowedClass < Exception
     def initialize action, klass_name
       super "Tried to #{action} unspecified class: #{klass_name}"
diff --git a/ext/psych/lib/psych/visitors/to_ruby.rb b/ext/psych/lib/psych/visitors/to_ruby.rb
index 935bc74f21..0bf5198ccc 100644
--- a/ext/psych/lib/psych/visitors/to_ruby.rb
+++ b/ext/psych/lib/psych/visitors/to_ruby.rb
@@ -427,7 +427,7 @@ module Psych
 
     class NoAliasRuby < ToRuby
       def visit_Psych_Nodes_Alias o
-        raise BadAlias, "Unknown alias: #{o.anchor}"
+        raise AliasesNotEnabled
       end
     end
   end