Improve missing param error message

Author: José Valim

lib/phoenix/exceptions.ex

@@ -15,7 +15,8 @@ defmodule Phoenix.MissingParamError do
   defexception [:message, plug_status: 400]
 
   def exception([key: value]) do
-    msg = "expected key for #{inspect value} to be present"
+    msg = "expected key #{inspect value} to be present in params, " <>
+          "please send the expected key or adapt your scrub_params/2 call"
     %Phoenix.MissingParamError{message: msg}
   end
 end

test/phoenix/controller/controller_test.exs

@@ -333,11 +333,11 @@ defmodule Phoenix.Controller.ControllerTest do
   end
 
   test "scrub_params/2 raises Phoenix.MissingParamError for missing key" do
-    assert_raise(Phoenix.MissingParamError, "expected key for \"foo\" to be present", fn ->
+    assert_raise(Phoenix.MissingParamError, ~r"expected key \"foo\" to be present in params", fn ->
       conn(:get, "/") |> fetch_query_params |> scrub_params("foo")
     end)
 
-    assert_raise(Phoenix.MissingParamError, "expected key for \"foo\" to be present", fn ->
+    assert_raise(Phoenix.MissingParamError, ~r"expected key \"foo\" to be present in params", fn ->
       conn(:get, "/?foo=") |> fetch_query_params |> scrub_params("foo")
     end)
   end