Fixes how errors are passed to list & struct children.

wagtail_react_streamfield/blocks/block.py

@@ -16,6 +16,19 @@ def get_default(self):
             default = default()
         return default
 
+    def get_children_errors(self, errors):
+        if errors:
+            if len(errors) > 1:
+                # We rely on Block.get_children_errors throwing
+                # a single ValidationError with a specially crafted 'params'
+                # attribute that we can pull apart and distribute
+                # to the child blocks.
+                raise TypeError(
+                    'Block.get_children_errors unexpectedly '
+                    'received multiple errors.'
+                )
+            return errors.as_data()[0].params
+
     def prepare_value(self, value, errors=None):
         """
         Returns the value as it will be displayed in react-streamfield.

wagtail_react_streamfield/blocks/list_block.py

@@ -54,8 +54,7 @@ def value_from_datadict(self, data, files, prefix):
             for child_block_data in data['value']]
 
     def prepare_value(self, value, errors=None):
-        children_errors = (None if errors is None
-                           else errors.as_data()[0].params)
+        children_errors = self.get_children_errors(errors)
         if children_errors is None:
             children_errors = [None] * len(value)
         prepared_value = []
@@ -67,7 +66,7 @@ def prepare_value(self, value, errors=None):
                 'type': self.child_block.name,
                 'hasError': bool(child_errors),
                 'value': self.child_block.prepare_value(child_value,
-                                                        errors=errors),
+                                                        errors=child_errors),
             })
             if html is not None:
                 child_value['html'] = html

wagtail_react_streamfield/blocks/stream_block.py

@@ -53,8 +53,9 @@ def value_from_datadict(self, data, files, prefix):
     def prepare_value(self, value, errors=None):
         if value is None:
             return []
-        children_errors = ({} if errors is None
-                           else errors.as_data()[0].params)
+        children_errors = self.get_children_errors(errors)
+        if children_errors is None:
+            children_errors = {}
         prepared_value = []
         for i, stream_child in enumerate(value):
             child_errors = children_errors.get(i)

wagtail_react_streamfield/blocks/struct_block.py

@@ -58,8 +58,9 @@ def value_from_datadict(self, data, files, prefix):
         ])
 
     def prepare_value(self, value, errors=None):
-        children_errors = ({} if errors is None
-                           else errors.as_data()[0].params)
+        children_errors = self.get_children_errors(errors)
+        if children_errors is None:
+            children_errors = {}
         prepared_value = []
         for k, child_block in self.child_blocks.items():
             child_errors = (None if children_errors is None
@@ -71,7 +72,8 @@ def prepare_value(self, value, errors=None):
                 'id': str(uuid4()),
                 'type': k,
                 'hasError': bool(child_errors),
-                'value': child_block.prepare_value(child_value, errors=errors),
+                'value': child_block.prepare_value(child_value,
+                                                   errors=child_errors),
             })
             if html is not None:
                 child_value['html'] = html

wagtail_react_streamfield/monkey_patch.py

@@ -63,9 +63,9 @@ def patch():
     _patch_streamfield_panel()
     _patch_block_widget()
     _patch_with(Block, NewBlock,
-                'FIELD_NAME_TEMPLATE', 'get_default', 'prepare_value',
-                'get_instance_html', 'definition', 'html_declarations',
-                'all_html_declarations')
+                'FIELD_NAME_TEMPLATE', 'get_default', 'get_children_errors',
+                'prepare_value', 'get_instance_html', 'definition',
+                'html_declarations', 'all_html_declarations')
     Block._meta_class.closed = False
     _patch_with(BaseStreamBlock, NewBaseStreamBlock,
                 'definition', 'sorted_child_blocks', 'render_list_member',