Interactive staging errors out

[tristan-unity]

Describe the bug
The interactive staging, where you can stage by chunks/lines does not appear to work.

To Reproduce
Steps to reproduce the behavior:

1. Create an empty repository git init.
2. Create a file containing two lines.

line one
line two

3. Commit the file.
4. Edit the file.

line one and something
line two
line three

5. Select the file and press enter to go the staging view.
6. Select the first chunk line one and something.
7. Stage the chunk

Screenshots

Screen.Recording.2025-02-04.at.6.36.57.pm.mov

Version info:

~/g/lazygit-interactive-staging-repro (master)> lazygit --version
commit=, build date=, build source=homebrew, version=0.45.2, os=darwin, arch=arm64, git version=2.48.1

~/g/lazygit-interactive-staging-repro (master)> git --version
git version 2.48.1

Additional context
OS: MacOS
Terminal Emulator: Ghostty
Shell: fish

I have used git add -p to stage the first chunk.

~/g/lazygit-interactive-staging-repro (master)> git diff
diff --git a/test.txt b/test.txt
index e5c5c55..9b53c18 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,3 @@
-line one
+line one and something
 line two
+line three

~/g/lazygit-interactive-staging-repro (master)> git add -p test.txt
diff --git a/test.txt b/test.txt
index e5c5c55..9b53c18 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,3 @@
-line one
+line one and something
 line two
+line three
(1/1) Stage this hunk [y,n,q,a,d,s,e,p,?]? e

~/g/lazygit-interactive-staging-repro (master)> git diff --cached
diff --git a/test.txt b/test.txt
index e5c5c55..92186d0 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,2 @@
-line one
+line one and something
 line two

I then used git diff --cached > p.patch to make patch that should be similar to what I imagine lazygit is using.

~/g/lazygit-interactive-staging-repro (master)> git diff --cached > p.patch
~/g/lazygit-interactive-staging-repro (master)> cat p.patch
diff --git a/test.txt b/test.txt
index e5c5c55..92186d0 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,2 @@
-line one
+line one and something
 line two

I then reset the staging area with git restore --staged test.txt.

~/g/lazygit-interactive-staging-repro (master)> git restore --staged test.txt
~/g/lazygit-interactive-staging-repro (master)> git diff
diff --git a/test.txt b/test.txt
index e5c5c55..9b53c18 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,3 @@
-line one
+line one and something
 line two
+line three

Finally I used git apply --cached p.patch and the patch was applied succesfully.

~/g/lazygit-interactive-staging-repro (master)> git apply --cached p.patch
~/g/lazygit-interactive-staging-repro (master)> git diff
diff --git a/test.txt b/test.txt
index 92186d0..9b53c18 100644
--- a/test.txt
+++ b/test.txt
@@ -1,2 +1,3 @@
 line one and something
 line two
+line three

[stefanhaller]

This seems to happen only with a diff context size of 0. (Press { until it's zero.) Are you using that intentionally?

If I follow your command line scenario and create the patch using git diff --cached -U0 > p.patch, trying to apply it fails with the same error message that lazygit gives.

I'm not going to investigate more at this point, but maybe this gives you clues what else to experiment with.

We only recently allowed to set the context size all the way down to 0; maybe that wasn't a good idea... (?)

[stefanhaller]

Interesting discussion in the magit repo: magit/magit#4222

What they ended up doing is disabling staging/unstaging when the context size is 0, and I suppose we should simply do the same. The result is pretty much the same as what we have now, except that the error message would be less confusing.

PRs welcome. :)

[stefanhaller]

Heck, it was such an easy change that I just made a PR: #4235