set_flash.now works only if called before any other qualifier

In the 3.0.0 `set_flash[:foo].now` is no longer a valid syntax, only the
`set_flash.now[:foo]` is valid[1].

Since this can create a false positive when people updating, we will raise a
exception to make the things more explicit.

[1]: https://github.com/thoughtbot/shoulda-matchers/pull/752

NEWS.md

@@ -86,6 +86,11 @@
   * `set_session['key'].to(nil)` will no longer pass when the key in question
     has not been set yet. ([535fe05])
 
+* Change `set_flash` so that `set_flash[:foo].now` is no longer valid syntax.
+  You'll want to use `set_flash.now[:foo]` instead. This was changed in order to
+  more closely align with how `flash.now` works when used in a controller.
+  ([#755], [#752])
+
 * Change behavior of `validate_uniqueness_of` when the matcher is not
   qualified with any scopes, but your validation is. Previously the following
   test would pass when it now fails:
@@ -115,6 +120,8 @@
 [535fe05]: https://github.com/thoughtbot/shoulda-matchers/commit/535fe05be8686fdafd8b22f2ed5c4192bd565d50
 [eaaa2d8]: https://github.com/thoughtbot/shoulda-matchers/commit/eaaa2d83e5cd31a3ca0a1aaa65441ea1a4fffa49
 [6ac7b81]: https://github.com/thoughtbot/shoulda-matchers/commit/6ac7b8158cfba3b518eb3da3c24345e4473b416f
+[#755]: https://github.com/thoughtbot/shoulda-matchers/pull/755
+[#752]: https://github.com/thoughtbot/shoulda-matchers/pull/752
 
 ### Bug fixes
 

lib/shoulda/matchers/action_controller/set_flash_matcher.rb

@@ -129,8 +129,8 @@ module Shoulda
       #         before { get :show }
       #
       #         it { should set_flash.now }
-      #         it { should set_flash[:foo].now }
-      #         it { should set_flash[:foo].to('bar').now }
+      #         it { should set_flash.now[:foo] }
+      #         it { should set_flash.now[:foo].to('bar') }
       #       end
       #     end
       #
@@ -140,8 +140,8 @@ module Shoulda
       #         setup { get :show }
       #
       #         should set_flash.now
-      #         should set_flash[:foo].now
-      #         should set_flash[:foo].to('bar').now
+      #         should set_flash.now[:foo]
+      #         should set_flash.now[:foo].to('bar')
       #       end
       #     end
       #
@@ -173,6 +173,10 @@ module Shoulda
         end
 
         def now
+          if key || expected_value
+            raise QualifierOrderError
+          end
+
           store = FlashStore.now
           @underlying_matcher = SetSessionOrFlashMatcher.new(store)
           self
@@ -184,18 +188,40 @@ module Shoulda
         end
 
         def [](key)
+          @key = key
           underlying_matcher[key]
           self
         end
 
         def to(expected_value = nil, &block)
+          @expected_value = expected_value
           underlying_matcher.to(expected_value, &block)
           self
         end
 
         protected
 
-        attr_reader :underlying_matcher
+        attr_reader :underlying_matcher, :key, :expected_value
+
+        # @private
+        class QualifierOrderError < StandardError
+          def message
+            <<-MESSAGE.strip
+Using `set_flash` with the `now` qualifier and specifying `now` after other
+qualifiers is no longer allowed.
+
+You'll want to use `now` immediately after `set_flash`. For instance:
+
+    # Valid
+    should set_flash.now[:foo]
+    should set_flash.now[:foo].to('bar')
+
+    # Invalid
+    should set_flash[:foo].now
+    should set_flash[:foo].to('bar').now
+            MESSAGE
+          end
+        end
       end
     end
   end

spec/unit/shoulda/matchers/action_controller/set_flash_matcher_spec.rb

@@ -40,4 +40,28 @@ describe Shoulda::Matchers::ActionController::SetFlashMatcher, type: :controller
       expect(controller).not_to set_flash.now['key for flash']
     end
   end
+
+  context 'when the now qualifier is called after the key is set' do
+    it 'raises a QualifierOrderError' do
+      controller = build_fake_response
+
+      usage = lambda do
+        expect(controller).to set_flash['any key'].now
+      end
+
+      expect(&usage).to raise_error(described_class::QualifierOrderError)
+    end
+  end
+
+  context 'when the now qualifier is called after the to qualifier' do
+    it 'raises a QualifierOrderError' do
+      controller = build_fake_response
+
+      usage = lambda do
+        expect(controller).to set_flash.to('any value').now
+      end
+
+      expect(&usage).to raise_error(described_class::QualifierOrderError)
+    end
+  end
 end