From 426d648681261edacd395e722b5d969b1eee018c Mon Sep 17 00:00:00 2001
From: epriestley <git@epriestley.com>
Date: Tue, 22 Dec 2015 06:09:38 -0800
Subject: [PATCH] In Drydock, don't reset current branch to point at unrelated
 commit

Summary:
Fixes T10037. When we're building commit `aabbccdd`, we currently do this to check it out:

  git reset --hard aabbccdd

However, this has an undesirable side effect of moving the current branch pointer to point at `aabbccdd`. The current branch pointer may be some totally different branch which `aabbccdd` is not part of, so this is confusing and misleading.

Instead, use `git reset --hard HEAD` to get the primary effect we want (destroying staged changes) and then `git checkout aabbccdd` to checkout the commit in a detached HEAD state.

Test Plan:
  - Ran a build (a commit-focused operation) successfully.
  - Verified working copy was pointed at a detached HEAD afterward:

```
builder@sbuild001:/var/drydock/workingcopy-167/repo/git-test-ii$ git status
HEAD detached at ffc7635
nothing to commit, working directory clean
```

  - Ran a land (a branch-foused operation) successfully.
  - Verified working copy was pointed at a branch afterward:

```
builder@sbuild001:/core/data/drydock/workingcopy-168/repo/git-test$ git status
On branch master
Your branch is up-to-date with 'origin/master'.

nothing to commit, working directory clean
```

Reviewers: chad

Reviewed By: chad

Subscribers: yelirekim

Maniphest Tasks: T10037

Differential Revision: https://secure.phabricator.com/D14850
---
 .../DrydockWorkingCopyBlueprintImplementation.php | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php b/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php
index f39353a8f4..d60a65580b 100644
--- a/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php
+++ b/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php
@@ -249,11 +249,15 @@ final class DrydockWorkingCopyBlueprintImplementation
 
       $ref = idx($spec, 'ref');
 
+      // Reset things first, in case previous builds left anything staged or
+      // dirty.
+      $cmd[] = 'git reset --hard HEAD';
+
       if ($commit !== null) {
-        $cmd[] = 'git reset --hard %s';
+        $cmd[] = 'git checkout %s --';
         $arg[] = $commit;
       } else if ($branch !== null) {
-        $cmd[] = 'git checkout %s';
+        $cmd[] = 'git checkout %s --';
         $arg[] = $branch;
 
         $cmd[] = 'git reset --hard origin/%s';
@@ -267,13 +271,8 @@ final class DrydockWorkingCopyBlueprintImplementation
         $arg[] = $ref_ref;
         $arg[] = $ref_ref;
 
-        $cmd[] = 'git checkout %s';
+        $cmd[] = 'git checkout %s --';
         $arg[] = $ref_ref;
-
-        $cmd[] = 'git reset --hard %s';
-        $arg[] = $ref_ref;
-      } else {
-        $cmd[] = 'git reset --hard HEAD';
       }
 
       $cmd = implode(' && ', $cmd);