Update gh pages task (#3762)

* Add task for updating github pages from develop

gulpfile.js

@@ -56,6 +56,7 @@ module.exports = {
   gitSyncMaster: gitTasks.syncMaster,
   gitCreateRC: gitTasks.createRC,
   gitRecompile: gitTasks.recompile,
+  gitUpdateGithubPages: gitTasks.updateGithubPages,
   typings: typings.typings,
   package: packageTasks.package,
   checkLicenses: licenseTasks.checkLicenses

package.json

@@ -41,6 +41,7 @@
     "test:setupselenium": "selenium-standalone install --config=./tests/scripts/selenium-config.js",
     "test:startselenium": "selenium-standalone start --config=./tests/scripts/selenium-config.js",
     "typings": "gulp typings",
+    "updateGithubPages": "gulp gitUpdateGithubPages",
     "version": "gulp build && git add -A"
   },
   "main": "./index.js",

scripts/gulpfiles/git_tasks.js

@@ -21,7 +21,7 @@ const upstream_url = "https://github.com/google/blockly.git";
 function syncBranch(branchName) {
   return function(done) {
     execSync('git stash save -m "Stash for sync"', { stdio: 'inherit' });
-    execSync('git checkout ' + branchName, { stdio: 'inherit' });
+    checkoutBranch(branchName);
     execSync('git pull ' + upstream_url + ' ' + branchName,
         { stdio: 'inherit' });
     execSync('git push origin ' + branchName, { stdio: 'inherit' });
@@ -56,6 +56,13 @@ function getRCBranchName() {
   return 'rc_' + yyyy + '_' + mm;
 };
 
+// If branch does not exist then create the branch. 
+// If branch exists switch to branch.
+function checkoutBranch(branchName) {
+  execSync('git checkout ' + branchName + ' || git checkout -b ' + branchName,
+   { stdio: 'inherit' });
+}
+
 // Recompile and push to origin.
 const recompile = gulp.series(
   syncDevelop,
@@ -93,9 +100,20 @@ const createRC = gulp.series(
   },
 );
 
+// Update github pages with what is currently in develop.
+const updateGithubPages = gulp.series(
+  syncBranch('gh-pages'),
+  function(done) {
+    execSync('git pull ' + upstream_url + ' develop', { stdio: 'inherit' });
+    execSync('git push ' + upstream_url + ' gh-pages', { stdio: 'inherit' });
+    done();
+  }
+);
+
 module.exports = {
   syncDevelop: syncDevelop,
   syncMaster: syncMaster,
   createRC: createRC,
-  recompile: recompile
+  recompile: recompile,
+  updateGithubPages: updateGithubPages
 }