bug: `git_diff` picker uses preview's first line as `pos` instead of hunk start line

[sQVe]

Summary

When using Snacks.picker.git_diff() with a base option, each picker entry's line number reflects the first line of the rendered diff preview block rather than the actual hunk start line in the file. This causes incorrect jump targets when opening a file from the picker and wrong lnum values when sending results to the quickfix list via <c-q>.

Environment

• snacks.nvim: 9912042 (main, 2026-03-04)
• Neovim: v0.12.0-dev-2435+g18c5f06c9f
• OS: Linux

Steps to reproduce

-- Minimal config
Snacks.picker.git_diff({
  base = "origin/main", -- or any commit/branch
})

1. Open the picker. Each entry shows a file with a line number.
2. Select an entry and press <CR> — the cursor lands at the wrong line (often line 1).
3. Alternatively, press <c-q> to send all entries to the quickfix list. Every lnum is incorrect.

Repro

vim.env.LAZY_STDPATH = ".repro"
load(vim.fn.system("curl -s https://raw.githubusercontent.com/folke/lazy.nvim/main/bootstrap.lua"))()

require("lazy.minit").repro({
  spec = {
    { "folke/snacks.nvim", opts = {} },
  },
})

-- From a git repo on a branch that has commits ahead of main, run:
-- :lua Snacks.picker.git_diff({ base = "main" })

Expected behaviour

Each entry's pos (and the resulting quickfix lnum) should be the hunk start line on the right-hand side of the unified diff header — i.e. the +N value from @@ -a,b +N,M @@.

Actual behaviour

Entries use the first line of the rendered diff preview block as their pos, rather than the hunk start line from the @@ ... +N,M @@ header. Each entry's line number therefore reflects wherever the preview panel begins rendering, not the actual changed line in the file.

Investigation

The data flow for line numbers is:

1. snacks/picker/source/git.lua:261 — runs git diff --no-color --no-ext-diff --diff-filter=u [--merge-base <base>]
2. snacks/picker/source/diff.lua:112 — M.parse() iterates raw diff lines
3. snacks/picker/source/diff.lua:262 — M.parse_hunk_header() extracts right.line from @@ -a,b +line,count @@
4. snacks/picker/source/diff.lua:89 — add() sets pos = { line, 0 } on each item
5. snacks/picker/actions.lua:540 — setqflist() reads item.pos[1] as quickfix lnum

The static parsing logic in parse_hunk_header appears correct for standard unified diff output. For example, with the following actual diff produced by the repo under test:

@@ -108,39 +108,8 @@
@@ -154,7 +123,6 @@
@@ -12,14 +12,12 @@ some context
@@ -34,5 +32,4 @@ some context

The expected pos values are 108, 123, 12, and 32 respectively. The bug appears to be a runtime issue — either in how opts.group is propagated to Diff.diff(), or in how pos is overwritten downstream — rather than a parsing failure.

Notes

• The bug reproduces specifically with base set (branch diff via --merge-base). Untested without base.
• The source config sets group = false by default, which should produce one entry per hunk with individual h.line values. If group is inadvertently true at runtime, all hunks collapse into one entry per file using only block.hunks[1].line.
• Related past fixes that are already included in the version above: bug: cursor is off by one when jumping with auto_confirm = true #543 (1-0 indexing), fix(git): set diff.noprefix=false for git diff to ensure correct format #2174 (diff.noprefix=false).

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