fix #553 by implementing a better error and updating the README

CHANGELOG.md

@@ -7,6 +7,7 @@
 ## Fixed
 
  - [#554][] - Non-detailed error should not lose options when merged.
+ - [#553][] - Improve error handling and documentation for hash filter defaults.
 
 # [5.2.0][] (2022-10-22)
 
@@ -1372,3 +1373,4 @@ Example.run
   [#539]: https://github.com/AaronLasseigne/active_interaction/issues/539
   [#545]: https://github.com/AaronLasseigne/active_interaction/issues/545
   [#554]: https://github.com/AaronLasseigne/active_interaction/issues/554
+  [#553]: https://github.com/AaronLasseigne/active_interaction/issues/553

README.md

@@ -358,7 +358,8 @@ HashInteraction.run!(preferences: { newsletter: true, 'sweepstakes' => false })
 
 Setting default hash values can be tricky. The default value has to be either
 `nil` or `{}`. Use `nil` to make the hash optional. Use `{}` if you want to set
-some defaults for values inside the hash.
+some defaults for values inside the hash. If any nested filter uses a
+[lazy default](#defaults) then the hash must also use a lazy default.
 
 ``` rb
 hash :optional,

lib/active_interaction/filters/hash_filter.rb

@@ -25,7 +25,7 @@ class HashFilter < Filter
 
     register :hash
 
-    def process(value, context)
+    def process(value, context) # rubocop:disable Metrics/AbcSize
       input = super
 
       return HashInput.new(self, value: input.value, error: input.errors.first) if input.errors.first
@@ -36,6 +36,10 @@ def process(value, context)
       children = {}
 
       filters.each do |name, filter|
+        if filter.options[:default].is_a?(Proc) && !options[:default].is_a?(Proc)
+          raise InvalidDefaultError, "#{self.name}: must use a lazy default if any nested filter uses a lazy default"
+        end
+
         filter.process(input.value[name], context).tap do |result|
           value[name] = result.value
           children[name.to_sym] = result

spec/active_interaction/integration/hash_interaction_spec.rb

@@ -71,4 +71,36 @@
       end.to raise_error ActiveInteraction::InvalidDefaultError
     end
   end
+
+  context 'with a default' do
+    context 'with a lazy nested default' do
+      it 'raises an error' do
+        expect do
+          Class.new(ActiveInteraction::Base) do
+            hash :b, default: {} do
+              hash :x, default: -> { {} }
+            end
+          end
+        end.to raise_error ActiveInteraction::InvalidDefaultError
+      end
+    end
+  end
+
+  context 'with a lazy default' do
+    context 'with a lazy nested default' do
+      it 'returns the correct value' do
+        klass = Class.new(ActiveInteraction::Base) do
+          hash :b, default: -> { {} } do
+            hash :x, default: -> { {} }
+          end
+
+          def execute
+            b
+          end
+        end
+
+        expect(klass.run!).to eql('x' => {})
+      end
+    end
+  end
 end