Avoid creating a core CJS bundle by re-using main bundle exports

These changes help avoid creating a CJS specific bundle for
`@apollo/client/core` by comparing `dist/apollo-client.cjs.js`
and `dist/react/index.js` exports, then re-exporting all
non-React exports from the main CJS bundle.

config/prepareDist.js

@@ -11,8 +11,13 @@
 // - Create a new `package.json` for each sub-set bundle we support, and
 //   store it in the appropriate dist sub-directory.
 
-const packageJson = require('../package.json');
 const fs = require('fs');
+const recast = require('recast');
+
+
+/* @apollo/client */
+
+const packageJson = require('../package.json');
 
 // The root package.json is marked as private to prevent publishing
 // from happening in the root of the project. This sets the package back to
@@ -44,6 +49,9 @@ const destDir = `${srcDir}/dist`;
 fs.copyFileSync(`${srcDir}/README.md`,  `${destDir}/README.md`);
 fs.copyFileSync(`${srcDir}/LICENSE`,  `${destDir}/LICENSE`);
 
+
+/* @apollo/client/core */
+
 function buildPackageJson(bundleName) {
   return JSON.stringify({
     name: `@apollo/client/${bundleName}`,
@@ -60,3 +68,35 @@ fs.writeFileSync(
   `${__dirname}/../dist/core/package.json`,
   buildPackageJson('core')
 );
+
+// Build a new `core.cjs.js` entry point file, that includes everything
+// except the exports listed in `src/react/index.ts`. Copy this file into
+// the `dist/core` directory, to allow Apollo Client core only imports
+// using `@apollo/client/core`.
+
+const reactIndexSrc = fs.readFileSync(`${__dirname}/../dist/react/index.js`);
+const reactExports = [];
+const ast = recast.parse(reactIndexSrc);
+recast.visit(ast, {
+  visitExportSpecifier(path) {
+    reactExports.push(path.value.exported.name);
+    return false;
+  }
+});
+
+const coreCjs = [
+  "const allExports = require('../apollo-client.cjs');",
+  `const filteredExports =
+    Object.keys(allExports)
+      .filter(key => !['${reactExports.join("', '")}'].includes(key))
+      .reduce((acc, key) => {
+        acc[key] = allExports[key];
+        return acc;
+      }, {});`,
+  "module.exports = filteredExports;"
+].join('\n');
+
+fs.writeFileSync(
+  `${__dirname}/../dist/core/core.cjs.js`,
+  coreCjs
+);

config/rollup.config.js

@@ -4,6 +4,8 @@ import { terser as minify } from 'rollup-plugin-terser';
 import cjs from 'rollup-plugin-commonjs';
 import fs from 'fs';
 
+import packageJson from '../package.json';
+
 const distDir = './dist';
 
 const globals = {
@@ -137,24 +139,12 @@ function prepareTesting() {
   };
 }
 
-import packageJson from '../package.json';
-const corePackageJson = require(`../${distDir}/core/package.json`);
-const coreDir = `${distDir}/core`;
-
 function rollup() {
   return [
-    // @apollo/client
     prepareESM(packageJson.module, distDir),
     prepareCJS(packageJson.module, packageJson.main),
     prepareCJSMinified(packageJson.main),
     prepareTesting(),
-
-    // @apollo/client/core
-    prepareCJS(
-      `${coreDir}/${corePackageJson.module}`,
-      `${coreDir}/${corePackageJson.main}`
-    ),
-    prepareCJSMinified(`${coreDir}/${corePackageJson.main}`),
   ];
 }
 

package.json

@@ -30,7 +30,7 @@
   "scripts": {
     "prebuild": "npm run clean",
     "build": "npx tsc",
-    "postbuild": "npm run prepdist && npm run bundle",
+    "postbuild": "npm run bundle && npm run prepdist",
     "watch": "npx tsc-watch --onSuccess \"npm run postbuild\"",
     "clean": "npx rimraf -r dist coverage lib",
     "test": "jest --config ./config/jest.config.js",
@@ -89,6 +89,7 @@
     "prop-types": "15.7.2",
     "react": "^16.11.0",
     "react-dom": "^16.11.0",
+    "recast": "^0.18.5",
     "rimraf": "^3.0.0",
     "rollup": "1.21.2",
     "rollup-plugin-commonjs": "^10.1.0",

src/index.ts

@@ -1,21 +1,2 @@
-/* Core */
-
 export * from './core';
-
-/* React */
-
-export { ApolloProvider } from './react/context/ApolloProvider';
-export { ApolloConsumer } from './react/context/ApolloConsumer';
-export {
-  getApolloContext,
-  resetApolloContext,
-  ApolloContextValue
-} from './react/context/ApolloContext';
-export { useQuery } from './react/hooks/useQuery';
-export { useLazyQuery } from './react/hooks/useLazyQuery';
-export { useMutation } from './react/hooks/useMutation';
-export { useSubscription } from './react/hooks/useSubscription';
-export { useApolloClient } from './react/hooks/useApolloClient';
-export { RenderPromises } from './react/ssr/RenderPromises';
-export * from './react/types/types';
-export * from './react/parser/parser';
+export * from './react';

src/react/index.ts

@@ -0,0 +1,21 @@
+export { ApolloProvider } from './context/ApolloProvider';
+export { ApolloConsumer } from './context/ApolloConsumer';
+export {
+  getApolloContext,
+  resetApolloContext,
+  ApolloContextValue
+} from './context/ApolloContext';
+export { useQuery } from './hooks/useQuery';
+export { useLazyQuery } from './hooks/useLazyQuery';
+export { useMutation } from './hooks/useMutation';
+export { useSubscription } from './hooks/useSubscription';
+export { useApolloClient } from './hooks/useApolloClient';
+export { RenderPromises } from './ssr/RenderPromises';
+export {
+  DocumentType,
+  IDocumentDefinition,
+  operationName,
+  parser
+} from './parser/parser';
+
+export * from './types/types';