1 files changed, 17 insertions, 15 deletions

diff --git a/activesupport/lib/active_support/core_ext/hash/keys.rb b/activesupport/lib/active_support/core_ext/hash/keys.rb
index b4c451ace4..3d41aa8572 100644
--- a/activesupport/lib/active_support/core_ext/hash/keys.rb
+++ b/activesupport/lib/active_support/core_ext/hash/keys.rb
@@ -1,10 +1,10 @@
 class Hash
-  # Return a new hash with all keys converted using the block operation.
+  # Returns a new hash with all keys converted using the block operation.
   #
   #  hash = { name: 'Rob', age: '28' }
   #
   #  hash.transform_keys{ |key| key.to_s.upcase }
-  #  # => { "NAME" => "Rob", "AGE" => "28" }
+  #  # => {"NAME"=>"Rob", "AGE"=>"28"}
   def transform_keys
     result = {}
     each_key do |key|
@@ -22,12 +22,12 @@ class Hash
     self
   end
 
-  # Return a new hash with all keys converted to strings.
+  # Returns a new hash with all keys converted to strings.
   #
   #   hash = { name: 'Rob', age: '28' }
   #
   #   hash.stringify_keys
-  #   #=> { "name" => "Rob", "age" => "28" }
+  #   # => { "name" => "Rob", "age" => "28" }
   def stringify_keys
     transform_keys{ |key| key.to_s }
   end
@@ -38,13 +38,13 @@ class Hash
     transform_keys!{ |key| key.to_s }
   end
 
-  # Return a new hash with all keys converted to symbols, as long as
+  # Returns a new hash with all keys converted to symbols, as long as
   # they respond to +to_sym+.
   #
   #   hash = { 'name' => 'Rob', 'age' => '28' }
   #
   #   hash.symbolize_keys
-  #   #=> { name: "Rob", age: "28" }
+  #   # => { name: "Rob", age: "28" }
   def symbolize_keys
     transform_keys{ |key| key.to_sym rescue key }
   end
@@ -61,24 +61,26 @@ class Hash
   # on a mismatch. Note that keys are NOT treated indifferently, meaning if you
   # use strings for keys but assert symbols as keys, this will fail.
   #
-  #   { name: 'Rob', years: '28' }.assert_valid_keys(:name, :age) # => raises "ArgumentError: Unknown key: years"
-  #   { name: 'Rob', age: '28' }.assert_valid_keys('name', 'age') # => raises "ArgumentError: Unknown key: name"
+  #   { name: 'Rob', years: '28' }.assert_valid_keys(:name, :age) # => raises "ArgumentError: Unknown key: :years. Valid keys are: :name, :age"
+  #   { name: 'Rob', age: '28' }.assert_valid_keys('name', 'age') # => raises "ArgumentError: Unknown key: :name. Valid keys are: 'name', 'age'"
   #   { name: 'Rob', age: '28' }.assert_valid_keys(:name, :age)   # => passes, raises nothing
   def assert_valid_keys(*valid_keys)
     valid_keys.flatten!
     each_key do |k|
-      raise ArgumentError.new("Unknown key: #{k}") unless valid_keys.include?(k)
+      unless valid_keys.include?(k)
+        raise ArgumentError.new("Unknown key: #{k.inspect}. Valid keys are: #{valid_keys.map(&:inspect).join(', ')}")
+      end
     end
   end
 
-  # Return a new hash with all keys converted by the block operation.
+  # Returns a new hash with all keys converted by the block operation.
   # This includes the keys from the root hash and from all
   # nested hashes.
   #
   #  hash = { person: { name: 'Rob', age: '28' } }
   #
   #  hash.deep_transform_keys{ |key| key.to_s.upcase }
-  #  # => { "PERSON" => { "NAME" => "Rob", "AGE" => "28" } }
+  #  # => {"PERSON"=>{"NAME"=>"Rob", "AGE"=>"28"}}
   def deep_transform_keys(&block)
     result = {}
     each do |key, value|
@@ -98,14 +100,14 @@ class Hash
     self
   end
 
-  # Return a new hash with all keys converted to strings.
+  # Returns a new hash with all keys converted to strings.
   # This includes the keys from the root hash and from all
   # nested hashes.
   #
   #   hash = { person: { name: 'Rob', age: '28' } }
   #
   #   hash.deep_stringify_keys
-  #   # => { "person" => { "name" => "Rob", "age" => "28" } }
+  #   # => {"person"=>{"name"=>"Rob", "age"=>"28"}}
   def deep_stringify_keys
     deep_transform_keys{ |key| key.to_s }
   end
@@ -117,14 +119,14 @@ class Hash
     deep_transform_keys!{ |key| key.to_s }
   end
 
-  # Return a new hash with all keys converted to symbols, as long as
+  # Returns a new hash with all keys converted to symbols, as long as
   # they respond to +to_sym+. This includes the keys from the root hash
   # and from all nested hashes.
   #
   #   hash = { 'person' => { 'name' => 'Rob', 'age' => '28' } }
   #
   #   hash.deep_symbolize_keys
-  #   # => { person: { name: "Rob", age: "28" } }
+  #   # => {:person=>{:name=>"Rob", :age=>"28"}}
   def deep_symbolize_keys
     deep_transform_keys{ |key| key.to_sym rescue key }
   end