tl;dr I did git reset HEAD without thinking, but was able to recover my lost work using a helpful git feature that I wanted to highlight. Learn from my mistakes and how to undo them.

I’ve been working on changes for a local project when my editor started spewing weird linter errors, so I went digging a little to fix that. This involved restarting vim several times. My computer had also crashed a couple times in recent days which left several .swp files dangling. I had been good about removing most of them but I missed one .swo file that was remaining. Long story short when I recovered from this file it removed several hours worth of recent changes.

No worries though, I’ll just restore from the last commit right? Except it wasn’t until after I ran git reset HEAD that I realized my latest commit was several hours old. Thankfully I had run git add consistently, so I knew my changes existed somewhere in my local object store. They just weren’t tied to a commit or really any tracking tools.

Enter git fsck --lost-found

--lost-found
    Write dangling objects into .git/lost-found/commit/ or
    .git/lost-found/other/, depending on type. If the object is a blob, the
    contents are written into the file, rather than its object name.

My changes existed somewhere as a dangling blob in the object store, so with a list of these blobs I figured I might be able to recover. Turns out it was much easier than I though it’d be.

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$ git fsck --lost-found | grep blob | tail -5
Checking object directories: 100% (256/256), done.
Checking objects: 100% (3986/3986), done.
dangling blob 7cfd69a20f6fe079b76e0eac62585acb544edd57
dangling blob f43e095668cdcb2274936e2cfdb86b3ef4326f62
dangling blob f6fee461567174ad01662420347bf979569de806
dangling blob 43ff423b391e642b53083bbe00f361863ff67ab2
dangling blob e17f0d9bed49f29d1fe101332a79026a54620a92

Other than just writing out objects to the .git/lost-found dir, git fsck also prints the blobs/commits it finds dangling. We can extract these blobs and grep through them to hopefully find my changes.

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$ for blob in $(git fsck --lost-found | grep blob | cut -d ' ' -f3); \
    do git cat-file -p $blob | grep "package foobar" && echo $blob; done
Checking object directories: 100% (256/256), done.
Checking objects: 100% (3986/3986), done.
package foobar 
069dac305daa21948d2ec3f52f2b680992b58fec
$ git cat-file -p 069dac305daa21948d2ec3f52f2b680992b58fec | head
package foobar
 
import (
        "fmt"
...

In sum, firstly don’t get into this state

• Commit early and often, you can clean up changes later
• Don’t blindly reload from old swp files
• Don’t blindly run git reset

If you ignore all that advice though and lose some changes, all hope isn’t lost. Git has some extremely useful recovery tools if you know where to look.