Add populate exchange (#120)

* Populate exchange

* Fix linting

* Add missing snapshots

* Use heler fns

* Add imports

* Add types for error codes (still not very clear)

src/__snapshots__/populate.test.ts.snap

@@ -0,0 +1,114 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`on (query w/ fragment) -> mutation mutation query matches snapshot 1`] = `
+"mutation MyMutation {
+  addTodo {
+    ...Todo_PopulateFragment_0
+  }
+}
+
+fragment Todo_PopulateFragment_0 on Todo {
+  ...TodoFragment
+}
+
+fragment TodoFragment on Todo {
+  id
+  text
+}
+"
+`;
+
+exports[`on (query w/ unused fragment) -> mutation mutation query matches snapshot 1`] = `
+"mutation MyMutation {
+  addTodo {
+    ...Todo_PopulateFragment_0
+  }
+}
+
+fragment Todo_PopulateFragment_0 on Todo {
+  id
+  text
+}
+"
+`;
+
+exports[`on mutation mutation query matches snapshot 1`] = `
+"mutation MyMutation {
+  addTodo {
+    __typename
+  }
+}
+"
+`;
+
+exports[`on query -> (mutation w/ interface return type) mutation query matches snapshot 1`] = `
+"mutation MyMutation {
+  removeTodo {
+    ...Todo_PopulateFragment_0
+    ...User_PopulateFragment_0
+  }
+}
+
+fragment Todo_PopulateFragment_0 on Todo {
+  id
+  name
+}
+
+fragment User_PopulateFragment_0 on User {
+  id
+  text
+}
+"
+`;
+
+exports[`on query -> (mutation w/ union return type) mutation query matches snapshot 1`] = `
+"mutation MyMutation {
+  updateTodo {
+    ...User_PopulateFragment_0
+    ...Todo_PopulateFragment_0
+  }
+}
+
+fragment User_PopulateFragment_0 on User {
+  id
+  text
+}
+
+fragment Todo_PopulateFragment_0 on Todo {
+  id
+  name
+}
+"
+`;
+
+exports[`on query -> mutation mutation query matches snapshot 1`] = `
+"mutation MyMutation {
+  addTodo {
+    ...Todo_PopulateFragment_0
+    ...Todo_PopulateFragment_1
+  }
+}
+
+fragment Todo_PopulateFragment_0 on Todo {
+  id
+  text
+  creator {
+    id
+    name
+  }
+}
+
+fragment Todo_PopulateFragment_1 on Todo {
+  text
+}
+"
+`;
+
+exports[`on query -> teardown -> mutation mutation query matches snapshot 1`] = `
+"mutation MyMutation {
+  addTodo {
+    __typename
+  }
+}
+"
+`;

src/helpers/help.ts

@@ -4,7 +4,7 @@
 // You can read more about the messages themselves in `docs/help.md`
 
 import { Kind, ExecutableDefinitionNode, InlineFragmentNode } from 'graphql';
-import { Ref } from '../types';
+import { Ref, ErrorCode } from '../types';
 
 type DebugNode = ExecutableDefinitionNode | InlineFragmentNode;
 
@@ -37,7 +37,7 @@ const getDebugOutput = (): string =>
     ? '\n(Caused At: ' + currentDebugStack.current.join(', ') + ')'
     : '';
 
-export const invariant = (clause: any, message: string, code: number) => {
+export const invariant = (clause: any, message: string, code: ErrorCode) => {
   if (!clause) {
     let errorMessage = message || 'Minfied Error #' + code + '\n';
     if (process.env.NODE_ENV !== 'production') {
@@ -50,7 +50,7 @@ export const invariant = (clause: any, message: string, code: number) => {
   }
 };
 
-export const warn = (message: string, code: number) => {
+export const warn = (message: string, code: ErrorCode) => {
   if (!cache.has(message)) {
     console.warn(message + getDebugOutput() + helpUrl + code);
     cache.add(message);

src/index.ts

@@ -2,3 +2,4 @@ export * from './operations';
 export * from './types';
 export { Store } from './store';
 export { cacheExchange } from './exchange';
+export { populateExchange } from './populate';