fix(graphcache): Fix deadlocked layers between deferred and optimisti…

…c layers

.changeset/poor-items-shake.md

@@ -0,0 +1,5 @@
+---
+'@urql/exchange-graphcache': patch
+---
+
+Fix a deadlock condition in Graphcache's layers, which is caused by subscriptions (or other deferred layers) starting before one-off mutation layers. This causes the mutation to not be completed, which keeps its data preferred above the deferred layer. That in turn means that layers stop squashing, which causes new results to be missing indefinitely, when they overlap.

exchanges/graphcache/src/store/data.ts

@@ -161,11 +161,9 @@ export const clearDataState = () => {
     while (
       --i >= 0 &&
       data.refLock.has(data.optimisticOrder[i]) &&
-      data.commutativeKeys.has(data.optimisticOrder[i]) &&
-      !data.deferredKeys.has(data.optimisticOrder[i])
-    ) {
+      data.commutativeKeys.has(data.optimisticOrder[i])
+    )
       squashLayer(data.optimisticOrder[i]);
-    }
   }
 
   currentOwnership = null;
@@ -535,20 +533,17 @@ export const reserveLayer = (
 
   let index = data.optimisticOrder.indexOf(layerKey);
   if (index > -1) {
-    if (!data.commutativeKeys.has(layerKey) && !hasNext) {
-      data.optimisticOrder.splice(index, 1);
-      // Protect optimistic layers from being turned into non-optimistic layers
-      // while preserving optimistic data
+    data.optimisticOrder.splice(index, 1);
+    // Protect optimistic layers from being turned into non-optimistic layers
+    // while preserving optimistic data
+    if (!data.commutativeKeys.has(layerKey) && !hasNext)
       clearLayer(data, layerKey);
-    } else {
-      return;
-    }
   }
 
   // If the layer has future results then we'll move it past any layer that's
   // still empty, so currently pending operations will take precedence over it
   for (
-    index = 0;
+    index = index > -1 ? index : 0;
     hasNext &&
     index < data.optimisticOrder.length &&
     !data.deferredKeys.has(data.optimisticOrder[index]) &&