✨ Colorize filenames with conflicts when upgrading

Summary:
Visually show files merged with conflicts when running `react-native-git-upgrade`.

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After running `react-native-git-upgrade`, files with conflicts are not immediately recognised visually. With this patch, files with conflicts are highlighted in red.

![image](https://user-images.githubusercontent.com/771989/36086385-fc183baa-1006-11e8-8862-0867b82b7ec1.png)

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  CATEGORY
[----------]        TYPE
[ CLI      ]   [-------------]      LOCATION
[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAL  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
[ IOS      ]   [ FEATURE     ]   [ {Directory} ]   |-----------|
[ ANDROID  ]   [ MINOR       ]   [ {Framework} ] - | {Message} |
[----------]   [-------------]   [-------------]   |-----------|

[CATEGORY] [TYPE] [LOCATION] - MESSAGE

 EXAMPLES:

 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
-->
[CLI] [ENHANCEMENT] [react-native-git-upgrade/cliEntry.js] - Print files with conflicts in red.
Closes #17947

Differential Revision: D6977042

Pulled By: hramos

fbshipit-source-id: 3c67561ea3acbee227a7a0cf42857af4fb75c75c

react-native-git-upgrade/cliEntry.js

@@ -33,23 +33,32 @@ log.heading = 'git-upgrade';
 /**
  * Promisify the callback-based shelljs function exec
  * @param logOutput If true, log the stdout of the command.
+ * @param logger Custom logger to modify the output, invoked with the data and the stream.
  * @returns {Promise}
  */
-function exec(command, logOutput) {
+function exec(command, logOutput, logger = null) {
   return new Promise((resolve, reject) => {
     let stderr, stdout = '';
     const child = shell.exec(command, {async: true, silent: true});
 
     child.stdout.on('data', data => {
       stdout += data;
       if (logOutput) {
-        process.stdout.write(data);
+        if (logger) {
+          logger(data, process.stdout);
+        } else {
+          process.stdout.write(data);
+        }
       }
     });
 
     child.stderr.on('data', data => {
       stderr += data;
-      process.stderr.write(data);
+      if (logger) {
+        logger(data, process.stderr);
+      } else {
+        process.stderr.write(data);
+      }
     });
 
     child.on('exit', (code, signal) => {
@@ -359,7 +368,13 @@ async function run(requestedVersion, cliArgs) {
 
     try {
       log.info('Apply the patch');
-      await exec(`git apply --3way ${patchPath}`, true);
+      await exec(`git apply --3way ${patchPath}`, true, (data, stream) => {
+        if (data.indexOf('conflicts') >= 0 || data.startsWith('U ')) {
+          stream.write(`\x1b[31m${data}\x1b[0m`);
+        } else {
+          stream.write(data);
+        }
+      });
     } catch (err) {
       log.warn(
         'The upgrade process succeeded but there might be conflicts to be resolved. ' +