Fetch instead of pull if the working tree isn't tracking remote.

[yoichi]

Problem

I'm using ghq on a git repository. ghq get -u gives an error when I'm on a branch that has not been pushed to the remote.

Proposal

Invoke git fetch instead of git pull in such situation.

How to reproduce

~/ghq/github.com/x-motemen/ghq% git checkout -b local-branch
Switched to a new branch 'local-branch'
~/ghq/github.com/x-motemen/ghq% ghq get -u github.com/x-motemen/ghq
    update /Users/yoichi/ghq/github.com/x-motemen/ghq
       git pull --ff-only
There is no tracking information for the current branch.
Please specify which branch you want to merge with.
See git-pull(1) for details.

    git pull <remote> <branch>

If you wish to set tracking information for this branch you can do so with:

    git branch --set-upstream-to=<remote>/<branch> local-branch

     error failed to get "github.com/x-motemen/ghq": /usr/local/bin/git: exit status 1

[coveralls]

Pull Request Test Coverage Report for Build 139766044

• 6 of 8 (75.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.08%) to 85.646%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
vcs.go	6	8	75.0%

Totals
Change from base Build 126705609:	-0.08%
Covered Lines:	1080
Relevant Lines:	1261

---

💛 - Coveralls

[yoichi]

After I submit this PR, I found that we can judge the condition with the exit code of git rev-parse @{u}. The code will be simpler since it does not require output parsing.

Note: The 2 conditions are not same when the upstream is set and deleted.

• git rev-parse @{u} gives an error
• git status -b gives output like ## master...origin/master [gone]

[yoichi]

@{u} is also a bit better about the range of git versions it supports.

• @{u} is introduced in git/git@28fb843
• git status -b is introduced in git/git@05a59a0

[Songmu]

Yes, I also had trouble with this behavior when bundle updating. It's a good fix.

This change looks generally good. I'll check it out later.

[coveralls]

Pull Request Test Coverage Report for Build 139610110

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• 27 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.09%) to 85.636%

---

Files with Coverage Reduction	New Missed Lines	%
vcs.go	27	86.83%

Totals
Change from base Build 126705609:	-0.09%
Covered Lines:	1091
Relevant Lines:	1274

---

💛 - Coveralls