Add changes generated by pre-commit

Loosely related to #806 .

I sometimes find myself doing the following:

• Edit some files.
• Run git add -p and stage only some of my edits.
• Run git commit -m "Some message".
  • pre-commit stashes all the unstaged changes,
  • runs all hooks, which change the working tree,
  • pops the stashed edits,
  • and rejects the commit.

The changes generated by the pre-commit hooks are now intermixed with the unstaged edits. I can’t just run git add -u && !!, as that will stage too much. Instead I need to run git add -p and select only the unstaged changes generated by my hooks.

Could pre-commit generate a patch of changes it generates and store that patch in .git? Then I could do something like the following:

git add -p
git commit -m "Some message."
cat .git/pre-commit/patch
git apply --index .git/pre-commit/patch && !-2

Or is there already a way to do this?

[blueyed]

I often run into this myself…

A workaround is also to use git stash -k (--keep-index) before committing, so any changes from pre-commit can be added using git add -u.

But it needs to be done before.

I would like if pre-commit could just not restore the changes from the patch (optionally), allowing for git add -u, and then restoring it manually - a command to do so could be given for copy’n’paste.

[asottile]

as you’ve learned from #806 and #747 – pre-commit will not modify your staging area since this is judged as an unsafe operation

as for generating a patch, there is one which is stored in ~/.cache/pre-commit which represents the parts pre-commit unstages. You’re free to reverse-apply that, then staged, then commit, then apply the patch again and you’ll be back to your desired state.

Let me know if this works for you!

Here’s a sample workflow for that:

$ git diff --staged
diff --git a/t b/t
index f00c965..dc76404 100644
--- a/t
+++ b/t
@@ -1,6 +1,6 @@
 1
 2
-3
+3 # trailing whitespace 
 4
 5
 6
$ git diff
diff --git a/t b/t
index dc76404..8e6f928 100644
--- a/t
+++ b/t
@@ -4,7 +4,7 @@
 4
 5
 6
-7
+7 # don't stage me
 8
 9
 10

And when I commit:

$ git commit -m "hi"
[WARNING] Unstaged files detected.
[INFO] Stashing unstaged files to /Users/asottile/.cache/pre-commit/patch1544222126.
Trim Trailing Whitespace.................................................Failed
hookid: trailing-whitespace

Files were modified by this hook. Additional output:

Fixing t

Fix End of Files.........................................................Passed
Check Yaml...........................................(no files to check)Skipped
Check for added large files..............................................Passed
[INFO] Restored changes from /Users/asottile/.cache/pre-commit/patch1544222126.

Now I can remove the parts I didn’t want to commit:

$ git apply --reverse /Users/asottile/.cache/pre-commit/patch1544222126
$ git add -u
$ git diff --staged
diff --git a/t b/t
index f00c965..50cfb57 100644
--- a/t
+++ b/t
@@ -1,6 +1,6 @@
 1
 2
-3
+3 # trailing whitespace
 4
 5
 6

And then commit and then restore:

$ git commit -m "wat"
Trim Trailing Whitespace.................................................Passed
Fix End of Files.........................................................Passed
Check Yaml...........................................(no files to check)Skipped
Check for added large files..............................................Passed
[master 13f3873] wat
 1 file changed, 1 insertion(+), 1 deletion(-)
$ git apply /Users/asottile/.cache/pre-commit/patch1544222126
$ git diff
diff --git a/t b/t
index 50cfb57..6900639 100644
--- a/t
+++ b/t
@@ -4,7 +4,7 @@
 4
 5
 6
-7
+7 # don't stage me
 8
 9
 10