Allow state to be rendered multiple times (#4030)

* state render

* add test

* formatting

* changelog

CHANGELOG.md

@@ -6,7 +6,8 @@
 
 ## Bug Fixes:
 
-No changes to highlight.
+- Fixes bug where rendering the same `gr.State` across different Interfaces/Blocks within
+a larger Blocks would not work by [@abidlabs](https://github.com/abidlabs) in [PR 4030](https://github.com/gradio-app/gradio/pull/4030)
 
 ## Documentation Changes:
 

gradio/blocks.py

@@ -843,10 +843,13 @@ class Blocks(BlockContext):
                 raise DuplicateBlockError(
                     f"A block with id: {self._id} has already been rendered in the current Blocks."
                 )
-            if not set(Context.root_block.blocks).isdisjoint(self.blocks):
-                raise DuplicateBlockError(
-                    "At least one block in this Blocks has already been rendered."
-                )
+            overlapping_ids = set(Context.root_block.blocks).intersection(self.blocks)
+            for id in overlapping_ids:
+                # State componenents are allowed to be reused between Blocks
+                if not isinstance(self.blocks[id], components.State):
+                    raise DuplicateBlockError(
+                        "At least one block in this Blocks has already been rendered."
+                    )
 
             Context.root_block.blocks.update(self.blocks)
             Context.root_block.fns.extend(self.fns)

test/test_blocks.py

@@ -1036,6 +1036,24 @@ class TestRender:
             io3 = io2.render()
         assert io2 == io3
 
+    def test_no_error_if_state_rendered_multiple_times(self):
+        state = gr.State("")
+        gr.TabbedInterface(
+            [
+                gr.Interface(
+                    lambda _, x: (x, "I don't know"),
+                    inputs=[state, gr.Textbox()],
+                    outputs=[state, gr.Textbox()],
+                ),
+                gr.Interface(
+                    lambda s: (s, f"User question: {s}"),
+                    inputs=[state],
+                    outputs=[state, gr.Textbox(interactive=False)],
+                ),
+            ],
+            ["Ask question", "Show question"],
+        )
+
 
 class TestCancel:
     @pytest.mark.skipif(