Change fetch arguments up a bit, start migrating

src/js/git/commands.js

@@ -265,8 +265,20 @@ var commandConfig = {
       command.twoArgsImpliedOrigin(generalArgs);
       assertOriginSpecified(generalArgs);
 
-      if (generalArgs[1]) {
+      var firstArg = generalArgs[1];
-        var tracking = assertBranchIsRemoteTracking(engine, generalArgs[1]);
+      if (firstArg && isColonRefspec(firstArg)) {
+        var refspecParts = firstArg.split(':');
+        options.source = refspecParts[0];
+        options.destination = refspecParts[1];
+
+        // destination will be created by fetch, but check source
+        assertIsRef(engine.origin, options.source);
+      } else if (firstArg) {
+        // here is the deal -- its JUST like git push. the first arg
+        // is used as both the destination and the source, so we need
+        // to make sure it exists as the source on REMOTE and then
+        // the destination will be created locally
+        var tracking = assertBranchIsRemoteTracking(engine, firstArg);
         options.branches = [engine.refs[tracking]];
       }
 

src/js/git/index.js

@@ -1051,6 +1051,7 @@ GitEngine.prototype.fetch = function(options) {
       )
     ));
   }, this);
+
   if (!commitsToMake.length && !options.dontThrowOnNoFetch) {
     throw new GitError({
       msg: intl.str('git-error-origin-fetch-uptodate')

todo.txt

@@ -19,10 +19,6 @@ Argument things:
 
 aka fetch + merge, just like expected. ill probably still update o/master just for sanity. master is the source on the remote and HEAD is the source on local (place to merge). o/master gets updated regardless
 
-so "git push origin branchNotOnLocal" fails but "git push origin someBranch" will make the someBranch on remote.
-
-3) HOWEVER if I'm git push-ing on banana and I say "git push origin master" then it pretends Im checked out on master. aka master is both source and destination, as expected. this is really 3
-
 Cases to handle / things to edit
 =======================