Fix the parse error when specifying an unknown version.

Summary:
**Motivation**

When running `react-native-git-upgrade` with an unknown version, the error message isn't very helpful

**Test Plan**

- Publish the `master` branch to Sinopia
- Run `react-native-git-upgrade 0.666.0` inside a RN project
- Error message is `SyntaxError: Unexpected end of JSON input`
- Publish this branch to Sinopia
- Run `react-native-git-upgrade 0.666.0` inside a RN project
- Error message should be `Error: The specified version of React Native 0.666.0 doesn't exist.
Re-run the react-native-git-upgrade command with an existing version,
for example: "react-native-git-upgrade 0.38.0",
or without arguments to upgrade to the latest: "react-native-git-upgrade".`
Closes #11264

Differential Revision: D4265553

Pulled By: mkonicek

fbshipit-source-id: 8597eb09cc3397bfa6d2205a9b3bb30acfad530f

Author: ncuillery

react-native-git-upgrade/checks.js

@@ -54,21 +54,9 @@ function checkGitAvailable() {
   }
 }
 
-function checkNewVersionValid(newVersion, requestedVersion) {
-  if (!semver.valid(newVersion) && requestedVersion) {
-    throw new Error(
-      'The specified version of React Native ' + requestedVersion + ' doesn\'t exist.\n' +
-      'Re-run the react-native-git-upgrade command with an existing version,\n' +
-      'for example: "react-native-git-upgrade 0.38.0",\n' +
-      'or without arguments to upgrade to the latest: "react-native-git-upgrade".'
-    );
-  }
-}
-
 module.exports = {
   checkDeclaredVersion,
   checkMatchingVersions,
   checkReactPeerDependency,
   checkGitAvailable,
-  checkNewVersionValid,
 };

react-native-git-upgrade/cliEntry.js

@@ -10,6 +10,7 @@
 
 const fs = require('fs');
 const os = require('os');
+const assert = require('assert');
 const path = require('path');
 const shell = require('shelljs');
 const Promise = require('promise');
@@ -25,7 +26,6 @@ const {
   checkMatchingVersions,
   checkReactPeerDependency,
   checkGitAvailable,
-  checkNewVersionValid
 } = require('./checks');
 
 log.heading = 'git-upgrade';
@@ -96,6 +96,25 @@ function readPackageFiles(useYarn) {
   }
 }
 
+function parseInformationJsonOutput(jsonOutput, requestedVersion) {
+  try {
+    const output = JSON.parse(jsonOutput);
+    const newVersion = output.version;
+    const newReactVersionRange = output['peerDependencies.react'];
+
+    assert(semver.valid(newVersion));
+
+    return {newVersion, newReactVersionRange}
+  } catch (err) {
+    throw new Error(
+      'The specified version of React Native ' + requestedVersion + ' doesn\'t exist.\n' +
+      'Re-run the react-native-git-upgrade command with an existing version,\n' +
+      'for example: "react-native-git-upgrade 0.38.0",\n' +
+      'or without arguments to upgrade to the latest: "react-native-git-upgrade".'
+    );
+  }
+}
+
 
 function setupWorkingDir(tmpDir) {
   return new Promise((resolve, reject) => {
@@ -240,15 +259,11 @@ async function run(requestedVersion, cliArgs) {
 
     log.info('Get information from NPM registry');
     const viewCommand = 'npm view react-native@' + (requestedVersion || 'latest') + ' peerDependencies.react version --json';
-    const viewOutput = await exec(viewCommand, verbose).then(JSON.parse);
-    const newVersion = viewOutput.version;
-    const newReactVersionRange = viewOutput['peerDependencies.react'];
+    const jsonOutput = await exec(viewCommand, verbose);
+    const {newVersion, newReactVersionRange} = parseInformationJsonOutput(jsonOutput, requestedVersion);
     // Print which versions we're upgrading to
     log.info('Upgrading to React Native ' + newVersion + (newReactVersionRange ? ', React ' + newReactVersionRange : ''));
 
-    log.info('Check new version');
-    checkNewVersionValid(newVersion, requestedVersion);
-
     log.info('Setup temporary working directory');
     await setupWorkingDir(tmpDir);