Ensure @client @export variables in watched queries are updated

The changes made in #5946 helped address an issue where queries
with `@client @export` variables were making unnecessary
network requests. While those changes work, they're currently
preventing watched queries using `@client @export` from updating
the `@export`ed variable, as new data is received. This commit
fixes that issue.

CHANGELOG.md

@@ -142,6 +142,9 @@
 - Refined `useLazyQuery` types to help prevent runtime errors.  <br/>
   [@benmosher](https://github.com/benmosher) in [#5935](https://github.com/apollographql/apollo-client/pull/5935)
 
+- Make sure `@client @export` variables used in watched queries are updated each time the query receives new data that changes the value of the `@export` variable.  <br/>
+  [@hwillson](https://github.com/hwillson) in [#5986](https://github.com/apollographql/apollo-client/pull/5986)
+
 ## Apollo Client 2.6.8
 
 ### Apollo Client (2.6.8)

src/__tests__/local-state/export.ts

@@ -754,8 +754,7 @@ describe('@client @export tests', () => {
             });
             done();
           }
-
-          resultCount +=1;
+          resultCount += 1;
         }
       });
     }
@@ -904,4 +903,65 @@ describe('@client @export tests', () => {
       });
     }
   );
+
+  it(
+    "should update @client @export variables on each broadcast if they've " +
+    "changed",
+    done => {
+      const cache = new InMemoryCache();
+
+      const widgetCountQuery = gql`{ widgetCount @client }`;
+      cache.writeQuery({
+        query: widgetCountQuery,
+        data: {
+          widgetCount: 100
+        }
+      });
+
+      const client = new ApolloClient({
+        cache,
+        resolvers: {
+          Query: {
+            doubleWidgets(_, { widgetCount }) {
+              return widgetCount ? widgetCount * 2 : 0;
+            }
+          }
+        }
+      });
+
+      const doubleWidgetsQuery = gql`
+        query DoubleWidgets($widgetCount: Int!) {
+          widgetCount @client @export(as: "widgetCount")
+          doubleWidgets(widgetCount: $widgetCount) @client
+        }
+      `;
+
+      let count = 0;
+      const obs = client.watchQuery({ query: doubleWidgetsQuery });
+      obs.subscribe({
+        next({ data }) {
+          switch (count) {
+            case 0:
+              expect(data.widgetCount).toEqual(100);
+              expect(data.doubleWidgets).toEqual(200);
+
+              client.writeQuery({
+                query: widgetCountQuery,
+                data: {
+                  widgetCount: 500
+                }
+              });
+              break;
+            case 1:
+              expect(data.widgetCount).toEqual(500);
+              expect(data.doubleWidgets).toEqual(1000);
+              done();
+              break;
+            default:
+          }
+          count += 1;
+        },
+      });
+    }
+  );
 });

src/core/ObservableQuery.ts

@@ -590,10 +590,7 @@ export class ObservableQuery<
       iterateObserversSafely(this.observers, 'error', this.lastError = error);
     };
 
-    const {
-      hasClientExports,
-      serverQuery
-    } = queryManager.transform(this.options.query);
+    const { hasClientExports } = queryManager.transform(this.options.query);
 
     queryManager.observeQuery<TData>(queryId, this.options, {
       next: (result: ApolloQueryResult<TData>) => {
@@ -605,9 +602,8 @@ export class ObservableQuery<
           // Before calling `next` on each observer, we need to first see if
           // the query is using `@client @export` directives, and update
           // any variables that might have changed. If `@export` variables have
-          // changed, and the query is requesting both local and remote
-          // data, `setVariables` is used as a network refetch might be
-          // needed to pull in new data, using the updated `@export` variables.
+          // changed, `setVariables` is used to query the cache first, followed
+          // by the network if needed.
           if (hasClientExports) {
             queryManager.getLocalState().addExportedVariables(
               query,
@@ -618,11 +614,10 @@ export class ObservableQuery<
                 !result.loading &&
                 previousResult &&
                 fetchPolicy !== 'cache-only' &&
-                serverQuery &&
                 !equal(previousVariables, variables)
               ) {
                 this.setVariables(variables).then(updatedResult => {
-                  iterateObserversSafely(this.observers, 'next', updatedResult)
+                  iterateObserversSafely(this.observers, 'next', updatedResult);
                 });
               } else {
                 this.variables = this.options.variables = variables;