Fix git apply error during applying custom patch

[black-desk]

• PR Description

Man page of git apply says that:

  --unidiff-zero
      By default, git apply expects that the patch being applied is a
      unified diff with at least one line of context. This provides
      good safety measures, but breaks down when applying a diff
      generated with --unified=0. To bypass these checks use
      --unidiff-zero.

      Note, for the reasons stated above, the usage of context-free
      patches is discouraged.

Lazygit always render custom patch with zero context,
so this --unidiff-zero option is needed when pass such patch to
git apply.

Check https://github.com/black-desk/lazygit-bug-report-2025-04-29
for details.

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[stefanhaller]

Lazygit always render custom patch with zero context

This is not true; it only does this if you set your diff context size to 0 (by pressing { repeatedly) before starting to create a patch.

I don't think we should use the --unidiff-zero option; there are good reasons why git discourages this. Instead, we should show a better error message when users start to create a custom patch while the diff context is zero, similar to what we did for normal staging in #4235.

[black-desk]

Lazygit always render custom patch with zero context

This is not true; it only does this if you set your diff context size to 0 (by pressing { repeatedly) before starting to create a patch.

Oh, but I do not remember I have done this before. Is it defaults to zero?

I don't think we should use the --unidiff-zero option; there are good reasons why git discourages this. Instead, we should show a better error message when users start to create a custom patch while the diff context is zero, similar to what we did for normal staging in #4235.

[stefanhaller]

This is not true; it only does this if you set your diff context size to 0 (by pressing { repeatedly) before starting to create a patch.

Oh, but I do not remember I have done this before. Is it defaults to zero?

No, that would be very weird. It defaults to 3. It is stored in state.yml, so if you do set it to 0, this gets remembered across restarts of lazygit.

[black-desk]

This is not true; it only does this if you set your diff context size to 0 (by pressing { repeatedly) before starting to create a patch.

Oh, but I do not remember I have done this before. Is it defaults to zero?

No, that would be very weird. It defaults to 3. It is stored in state.yml, so if you do set it to 0, this gets remembered across restarts of lazygit.

I think might we should make sure it to be at least 1, as 0 is discouraged by git and will somehow make git apply do not work.

Or at least print something useful in log? I have been troubled by this issue for months.

[stefanhaller]

I think might we should make sure it to be at least 1,

It used to be limited to at least 1, but we changed it deliberately to allow 0 as well (in version 0.45, see #4050) because some people wanted this.

Or at least print something useful in log?

Not in the log, but show an error panel; that's what I suggested above. Here's a PR that does this: #4522

[black-desk]

I think might we should make sure it to be at least 1,

It used to be limited to at least 1, but we changed it deliberately to allow 0 as well (in version 0.45, see #4050) because some people wanted this.

Or at least print something useful in log?

Not in the log, but show an error panel; that's what I suggested above. Here's a PR that does this: #4522

Thanks.