Merge pull request #39347 from p8/did-you-mean-for-parameter-missing

Add DidYouMean for ParameterMissing

actionpack/lib/action_controller/metal/strong_parameters.rb

@@ -19,12 +19,36 @@ module ActionController
   #   params.require(:a)
   #   # => ActionController::ParameterMissing: param is missing or the value is empty: a
   class ParameterMissing < KeyError
-    attr_reader :param # :nodoc:
+    attr_reader :param, :keys # :nodoc:
 
-    def initialize(param) # :nodoc:
+    def initialize(param, keys = nil) # :nodoc:
       @param = param
+      @keys  = keys
       super("param is missing or the value is empty: #{param}")
     end
+
+    class Correction
+      def initialize(error)
+        @error = error
+      end
+
+      def corrections
+        if @error.param && @error.keys
+          maybe_these = @error.keys
+
+          maybe_these.sort_by { |n|
+            DidYouMean::Jaro.distance(@error.param.to_s, n)
+          }.reverse.first(4)
+        else
+          []
+        end
+      end
+    end
+
+    # We may not have DYM, and DYM might not let us register error handlers
+    if defined?(DidYouMean) && DidYouMean.respond_to?(:correct_error)
+      DidYouMean.correct_error(self, Correction)
+    end
   end
 
   # Raised when a supplied parameter is not expected and
@@ -480,7 +504,7 @@ def require(key)
       if value.present? || value == false
         value
       else
-        raise ParameterMissing.new(key)
+        raise ParameterMissing.new(key, @parameters.keys)
       end
     end
 
@@ -617,7 +641,7 @@ def fetch(key, *args)
           if block_given?
             yield
           else
-            args.fetch(0) { raise ActionController::ParameterMissing.new(key) }
+            args.fetch(0) { raise ActionController::ParameterMissing.new(key, @parameters.keys) }
           end
         }
       )

actionpack/test/controller/required_params_test.rb

@@ -22,6 +22,20 @@ class ActionControllerRequiredParamsTest < ActionController::TestCase
     end
   end
 
+  if defined?(DidYouMean) && DidYouMean.respond_to?(:correct_error)
+    test "exceptions have suggestions for fix" do
+      error = assert_raise ActionController::ParameterMissing do
+        post :create, params: { magazine: { name: "Mjallo!" } }
+      end
+      assert_match "Did you mean?", error.message
+
+      error = assert_raise ActionController::ParameterMissing do
+        post :create, params: { book: { title: "Mjallo!" } }
+      end
+      assert_match "Did you mean?", error.message
+    end
+  end
+
   test "required parameters that are present will not raise" do
     post :create, params: { book: { name: "Mjallo!" } }
     assert_response :ok