Reinstate stream_data as a deprecated property of StreamValue

This (hopefully) fully replicates the old behaviour of stream_data, returning raw JSON data for lazy StreamValues and the tuple representation for non-lazy values.

wagtail/core/blocks/stream_block.py

@@ -1,4 +1,5 @@
 import uuid
+import warnings
 
 from collections import OrderedDict, defaultdict
 from collections.abc import MutableSequence
@@ -14,6 +15,7 @@ from django.utils.translation import gettext as _
 
 from wagtail.admin.staticfiles import versioned_static
 from wagtail.core.utils import escape_script
+from wagtail.utils.deprecation import RemovedInWagtail214Warning
 
 from .base import Block, BoundBlock, DeclarativeSubBlocksMetaclass
 from .utils import indent, js_dict
@@ -421,6 +423,12 @@ class StreamValue(MutableSequence):
                 'id': self.id,
             }
 
+        def _as_tuple(self):
+            if self.id:
+                return (self.block.name, self.value, self.id)
+            else:
+                return (self.block.name, self.value)
+
     class RawDataView(MutableSequence):
         """
         Internal helper class to present the stream data in raw JSONish format. For backwards
@@ -460,6 +468,38 @@ class StreamValue(MutableSequence):
         def __repr__(self):
             return repr(list(self))
 
+    class TupleView(MutableSequence):
+        """
+        RemovedInWagtail214Warning:
+        Internal helper class to replicate the old behaviour of StreamValue.stream_data on a
+        non-lazy StreamValue. This only exists for backwards compatibility and can be dropped
+        once stream_data has been retired.
+        """
+        def __init__(self, stream_value):
+            self.stream_value = stream_value
+
+        def __getitem__(self, i):
+            # convert BoundBlock to tuple representation on retrieval
+            return self.stream_value[i]._as_tuple()
+
+        # all other methods can be proxied directly to StreamValue, since its assignment /
+        # insertion methods accept the tuple representation
+
+        def __len__(self):
+            return len(self.stream_value)
+
+        def __setitem__(self, i, item):
+            self.stream_value[i] = item
+
+        def __delitem__(self, i):
+            del self.stream_value[i]
+
+        def insert(self, i, item):
+            self.stream_value.insert(i, item)
+
+        def __repr__(self):
+            return repr(list(self))
+
     def __init__(self, stream_block, stream_data, is_lazy=False, raw_text=None):
         """
         Construct a StreamValue linked to the given StreamBlock,
@@ -536,6 +576,19 @@ class StreamValue(MutableSequence):
     def raw_data(self):
         return StreamValue.RawDataView(self)
 
+    @cached_property
+    def stream_data(self):
+        warnings.warn(
+            "The stream_data property of StreamField / StreamBlock values is deprecated.\n"
+            "HINT: Instead of value.stream_data[i], retrieve block objects with value[i] "
+            "or access the raw JSON-like data via value.raw_data[i].",
+            RemovedInWagtail214Warning
+        )
+        if self.is_lazy:
+            return StreamValue.RawDataView(self)
+        else:
+            return StreamValue.TupleView(self)
+
     def _prefetch_blocks(self, type_name):
         """
         Populate _bound_blocks with all items in this stream of type `type_name` that exist in