(core) - Fix Client hang on promisified sources

.changeset/empty-zoos-compete.md

@@ -0,0 +1,5 @@
+---
+'@urql/core': patch
+---
+
+Fix a condition under which the `Client` would hang when a query is started and consumed with `toPromise()`

packages/core/src/client.test.ts

@@ -10,6 +10,7 @@ import {
   subscribe,
   filter,
   toArray,
+  toPromise,
   tap,
   take,
 } from 'wonka';
@@ -893,4 +894,30 @@ describe('shared sources behavior', () => {
     );
     expect(resultTwo).toHaveBeenCalledTimes(0);
   });
+
+  it('supports promisified sources', async () => {
+    const exchange: Exchange = () => ops$ => {
+      return pipe(
+        ops$,
+        map(op => ({ stale: true, data: 1, operation: op }))
+      );
+    };
+
+    const client = createClient({
+      url: 'test',
+      exchanges: [exchange],
+    });
+
+    const resultOne = await pipe(
+      client.executeRequestOperation(queryOperation),
+      take(1),
+      toPromise
+    );
+
+    expect(resultOne).toEqual({
+      data: 1,
+      operation: queryOperation,
+      stale: true,
+    });
+  });
 });

packages/core/src/client.ts

@@ -2,6 +2,7 @@
 
 import {
   filter,
+  make,
   makeSubject,
   onEnd,
   onPush,
@@ -285,31 +286,37 @@ export class Client {
       };
     }
 
-    const prevReplay = activeOperation.replay;
-    const subject = makeSubject<OperationResult>();
     const isNetworkOperation =
       operation.context.requestPolicy === 'cache-and-network' ||
       operation.context.requestPolicy === 'network-only';
 
-    return pipe(
-      merge([subject.source, activeOperation.source]),
-      onStart(() => {
-        this.activeOperations.set(operation.key, activeOperation!);
-        if (operation.kind === 'subscription') {
-          return this.dispatchOperation(operation);
-        } else if (isNetworkOperation) {
-          this.dispatchOperation(operation);
-        }
-
-        if (prevReplay != null && prevReplay === activeOperation!.replay) {
-          subject.next(
-            isNetworkOperation ? { ...prevReplay, stale: true } : prevReplay
-          );
-        } else if (!isNetworkOperation) {
-          this.dispatchOperation(operation);
-        }
-      })
-    );
+    return make(observer => {
+      activeOperation =
+        this.activeOperations.get(operation.key) || activeOperation!;
+      const prevReplay = activeOperation.replay;
+
+      return pipe(
+        activeOperation.source,
+        onStart(() => {
+          this.activeOperations.set(operation.key, activeOperation!);
+          if (operation.kind === 'subscription') {
+            return this.dispatchOperation(operation);
+          } else if (isNetworkOperation) {
+            this.dispatchOperation(operation);
+          }
+
+          if (prevReplay != null && prevReplay === activeOperation!.replay) {
+            observer.next(
+              isNetworkOperation ? { ...prevReplay, stale: true } : prevReplay
+            );
+          } else if (!isNetworkOperation) {
+            this.dispatchOperation(operation);
+          }
+        }),
+        onEnd(observer.complete),
+        subscribe(observer.next)
+      ).unsubscribe;
+    });
   }
 
   query<Data = any, Variables extends object = {}>(