Fix uniqDynPure crashing after being reconnected

src/Specular/Internal/Incremental.purs

@@ -152,7 +152,14 @@ connect = mkEffectFn1 \node -> do
       pure unit
 
   value <- runEffectFn1 source.compute node
-  runEffectFn2 Node.set_value node value
+
+  -- Note: `compute` can return `none`, which means "do not update the value",
+  -- in cases where we're re-connecting a node which was previously alive.
+  -- In that case, don't erase the previous value.
+  if Optional.isSome value then
+    runEffectFn2 Node.set_value node value
+  else
+    pure unit
 
   runEffectFn1 Profiling.end mark
 

test/node/DynamicSpec.purs

@@ -167,6 +167,22 @@ spec = describe "Dynamic" $ do
       -- clean up
       liftEffect unsub1
 
+    it "works after disconnecting and reconnecting" $ withLeakCheck do
+      log <- liftEffect $ new []
+      root <- Ref.new 1
+      let dyn = uniqDynPure (Ref.value root)
+      unsub1 <- liftEffect $ execCleanupT do
+        subscribeEvent_ (append log) (changed dyn)
+      liftEffect unsub1
+
+      unsub2 <- liftEffect $ execCleanupT do
+        subscribeEvent_ (append log) (changed dyn)
+
+      readDynamic dyn `shouldReturn` 1
+
+      -- clean up
+      liftEffect unsub2
+
   describe "foldDynMaybe" $ do
     it "triggers only when function returns Just" $ withLeakCheck $ do
       { event, fire } <- liftEffect newEvent