feat(execute): Resolve promise context values (#2806)

Co-authored-by: Phil Pluckthun <phil@kitten.sh>

.changeset/olive-rings-yawn.md

@@ -0,0 +1,5 @@
+---
+'@urql/exchange-execute': minor
+---
+
+The `context` option, which may be set to a context value or a function returning a context, can now return a `Promise` and will be correctly resolved and awaited.

exchanges/execute/src/execute.test.ts

@@ -144,6 +144,33 @@ describe('on operation', () => {
     });
   });
 
+  it('calls execute after executing context as a function returning a Promise', async () => {
+    const context = async operation => {
+      expect(operation).toBe(queryOperation);
+      return 'CALCULATED_USER_ID=' + 8 * 10;
+    };
+
+    await pipe(
+      fromValue(queryOperation),
+      executeExchange({ schema, context })(exchangeArgs),
+      take(1),
+      toPromise
+    );
+
+    expect(mocked(execute)).toBeCalledTimes(1);
+    expect(mocked(execute)).toBeCalledWith({
+      schema,
+      document: queryOperation.query,
+      rootValue: undefined,
+      contextValue: 'CALCULATED_USER_ID=80',
+      variableValues: queryOperation.variables,
+      operationName: expectedQueryOperationName,
+      fieldResolver: undefined,
+      typeResolver: undefined,
+      subscribeFieldResolver: undefined,
+    });
+  });
+
   it('should return data from subscribe', async () => {
     const context = 'USER_ID=123';
 

exchanges/execute/src/execute.ts

@@ -46,14 +46,15 @@ const asyncIterator =
 
 const makeExecuteSource = (
   operation: Operation,
-  args: ExecuteParams
+  _args: ExecuteParams
 ): Source<OperationResult> => {
   return make<OperationResult>(observer => {
     let iterator: AsyncIterator<ExecutionResult>;
     let ended = false;
 
     Promise.resolve()
-      .then(() => {
+      .then(async () => ({ ..._args, contextValue: await _args.contextValue }))
+      .then(args => {
         if (ended) return;
         if (operation.kind === 'subscription') {
           return subscribe(args) as any;