From 6ed02ab06cea6abd9377b0d7f19be1a0c0c58742 Mon Sep 17 00:00:00 2001
From: Ash Wilson <smashwilson@github.com>
Date: Thu, 9 Aug 2018 16:03:57 -0400
Subject: [PATCH 1/2] Use deleteRef() to "reset" the initial commit

---
 lib/git-shell-out-strategy.js |  4 ++++
 test/git-strategies.test.js   | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/lib/git-shell-out-strategy.js b/lib/git-shell-out-strategy.js
index 011e07f83d..c8d5ae1a2b 100644
--- a/lib/git-shell-out-strategy.js
+++ b/lib/git-shell-out-strategy.js
@@ -812,6 +812,10 @@ export default class GitShellOutStrategy {
     return this.exec(['reset', `--${type}`, revision]);
   }
 
+  deleteRef(ref) {
+    return this.exec(['update-ref', '-d', ref]);
+  }
+
   /**
    * Branches
    */
diff --git a/test/git-strategies.test.js b/test/git-strategies.test.js
index b5c6c53c71..686138469d 100644
--- a/test/git-strategies.test.js
+++ b/test/git-strategies.test.js
@@ -714,6 +714,31 @@ import * as reporterProxy from '../lib/reporter-proxy';
       });
     });
 
+    describe('deleteRef()', function() {
+      it('soft-resets an initial commit', async function() {
+        const workingDirPath = await cloneRepository('three-files');
+        const git = createTestStrategy(workingDirPath);
+
+        // Ensure that three-files still has only a single commit
+        assert.lengthOf(await git.getCommits({max: 10}), 1);
+
+        // Put something into the index to ensure it doesn't get lost
+        fs.appendFileSync(path.join(workingDirPath, 'a.txt'), 'zzz\n', 'utf8');
+        await git.exec(['add', '.']);
+
+        await git.deleteRef('HEAD');
+
+        const after = await git.getCommit('HEAD');
+        assert.isTrue(after.unbornRef);
+
+        const stagedChanges = await git.getDiffsForFilePath('a.txt', {staged: true});
+        assert.lengthOf(stagedChanges, 1);
+        const stagedChange = stagedChanges[0];
+        assert.strictEqual(stagedChange.newPath, 'a.txt');
+        assert.deepEqual(stagedChange.hunks[0].lines, ['+foo', '+zzz']);
+      });
+    });
+
     describe('getBranches()', function() {
       const sha = '66d11860af6d28eb38349ef83de475597cb0e8b4';
 

From abd40e10fe8577f619ee3391d2f739dad12392b9 Mon Sep 17 00:00:00 2001
From: Ash Wilson <smashwilson@github.com>
Date: Thu, 9 Aug 2018 16:21:30 -0400
Subject: [PATCH 2/2] Fall back to update-ref -d on the initial commit

---
 lib/models/repository-states/present.js | 13 +++++-
 test/models/repository.test.js          | 57 +++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/lib/models/repository-states/present.js b/lib/models/repository-states/present.js
index c7b42da7c6..a6034a898b 100644
--- a/lib/models/repository-states/present.js
+++ b/lib/models/repository-states/present.js
@@ -341,7 +341,18 @@ export default class Present extends State {
         ...Keys.filePatch.eachWithOpts({staged: true}),
         Keys.headDescription,
       ],
-      () => this.git().reset('soft', 'HEAD~'),
+      async () => {
+        try {
+          await this.git().reset('soft', 'HEAD~');
+        } catch (e) {
+          if (/unknown revision/.test(e.stdErr)) {
+            // Initial commit
+            await this.git().deleteRef('HEAD');
+          } else {
+            throw e;
+          }
+        }
+      },
     );
   }
 
diff --git a/test/models/repository.test.js b/test/models/repository.test.js
index 0e7c9274d4..3003496211 100644
--- a/test/models/repository.test.js
+++ b/test/models/repository.test.js
@@ -575,6 +575,63 @@ describe('Repository', function() {
     });
   });
 
+  describe('undoLastCommit()', function() {
+    it('performs a soft reset', async function() {
+      const workingDirPath = await cloneRepository('multiple-commits');
+      const repo = new Repository(workingDirPath);
+      await repo.getLoadPromise();
+
+      fs.appendFileSync(path.join(workingDirPath, 'file.txt'), 'qqq\n', 'utf8');
+      await repo.git.exec(['add', '.']);
+      await repo.git.commit('add stuff');
+
+      const parentCommit = await repo.git.getCommit('HEAD~');
+
+      await repo.undoLastCommit();
+
+      const commitAfterReset = await repo.git.getCommit('HEAD');
+      assert.strictEqual(commitAfterReset.sha, parentCommit.sha);
+
+      const fp = await repo.getFilePatchForPath('file.txt', {staged: true});
+      assert.strictEqual(
+        fp.toString(),
+        dedent`
+          diff --git a/file.txt b/file.txt
+          --- a/file.txt
+          +++ b/file.txt
+          @@ -1,1 +1,2 @@
+           three
+          +qqq\n
+        `,
+      );
+    });
+
+    it('deletes the HEAD ref when only a single commit is present', async function() {
+      const workingDirPath = await cloneRepository('three-files');
+      const repo = new Repository(workingDirPath);
+      await repo.getLoadPromise();
+
+      fs.appendFileSync(path.join(workingDirPath, 'b.txt'), 'qqq\n', 'utf8');
+      await repo.git.exec(['add', '.']);
+
+      await repo.undoLastCommit();
+
+      const fp = await repo.getFilePatchForPath('b.txt', {staged: true});
+      assert.strictEqual(
+        fp.toString(),
+        dedent`
+          diff --git a/b.txt b/b.txt
+          new file mode 100644
+          --- /dev/null
+          +++ b/b.txt
+          @@ -0,0 +1,2 @@
+          +bar
+          +qqq\n
+        `,
+      );
+    });
+  });
+
   describe('fetch(branchName, {remoteName})', function() {
     it('brings commits from the remote and updates remote branch, and does not update branch', async function() {
       const {localRepoPath} = await setUpLocalAndRemoteRepositories({remoteAhead: true});