fix(diff): remove stale git sentinel after failed attach

[kozabaa]

fix(diff): remove stale git sentinel after failed attach

Problem

Opening a buffer in a directory that is not yet a git repository permanently blocks mini.diff from ever attaching to that buffer, even after git init is run later in the same session.

Symptoms:

• Gutter signs never appear after git init + commit
• MiniDiff.get_buf_data() always returns nil
• MiniDiff.enable() called manually has no effect
• No errors are logged anywhere

Root cause

In H.git_start_watching_index, when the initial git rev-parse --git-dir returns a non-zero exit code, on_not_in_git fires:

-- lua/mini/diff.lua  ~line 1696
local on_not_in_git = vim.schedule_wrap(function()
  if not vim.api.nvim_buf_is_valid(buf_id) then
    H.cache[buf_id] = nil
    return
  end
  MiniDiff.fail_attach(buf_id)
  H.git_cache[buf_id] = {}    -- ← stale sentinel
end)

The call chain is:

fail_attach(buf_id)
  → disable(buf_id)
      → source.detach(buf_id)
          → H.git_cache[buf_id] = nil   ✓  invariant restored
      → H.cache[buf_id] = nil           ✓  buffer marked as not attached
  ← returns
H.git_cache[buf_id] = {}               ✗  invariant violated

After detach correctly clears the entry to nil, on_not_in_git immediately overwrites it with an empty table {}. The attach guard then blocks every future re-attachment attempt for that buffer ID:

local attach = function(buf_id)
  if H.git_cache[buf_id] ~= nil then return false end  -- {} ~= nil → returns false
  ...
end

Because attach returns false, enable calls fail_attach again, which calls disable, which clears H.cache[buf_id]. As a result, get_buf_data() always returns nil and the buffer is permanently wedged for the rest of the Neovim session under that buffer ID.

Fix

Remove the one line that re-poisons the cache after detach has already cleaned it up:

   local on_not_in_git = vim.schedule_wrap(function()
     if not vim.api.nvim_buf_is_valid(buf_id) then
       H.cache[buf_id] = nil
       return
     end
     MiniDiff.fail_attach(buf_id)
-    H.git_cache[buf_id] = {}
   end)

Why this is safe

The sentinel's apparent purpose is to prevent re-attach storms after a failed attempt. That concern is already handled elsewhere:

1. detach already cleaned up. fail_attach → disable → source.detach sets H.git_cache[buf_id] = nil before the removed line ever ran. The extra assignment was redundant on top of being harmful.

2. No re-attach loop is possible. auto_enable is gated on H.is_buf_enabled(buf_id) and fires only on BufEnter. After fail_attach, H.cache[buf_id] is nil (buffer disabled); nothing schedules another enable until the user switches to the buffer again — which is exactly when a retry is wanted (the user may have just run git init).

3. The in-flight guard is unaffected. The attach function sets H.git_cache[buf_id] = {} synchronously before launching the async git rev-parse job (line 663). That assignment is what prevents a second concurrent attach during a live job. Removing the post-failure assignment does not touch this path.

Reproduction

# 1. Open Neovim in a non-git directory
cd /tmp/testdir && nvim hello.md

# 2. In another pane, while Neovim stays open:
git init /tmp/testdir
git -C /tmp/testdir add .
git -C /tmp/testdir commit -m "init"

# 3. Edit hello.md, then in Neovim:
:lua print(vim.inspect(MiniDiff.get_buf_data()))
-- Before fix: nil
-- After fix:  table with config/hunks/summary

Tested on

• Neovim 0.12.1

• Debian trixie-slim (Docker container, HOME=/tmp)

• mini.nvim main (confirmed by reading the source)

• I have read CONTRIBUTING.md

• I have read CODE_OF_CONDUCT.md

[krovuxdev]

It’s intentional, when it’s nil it means the buffer is empty or the file isn’t being used, and also if the file wasn’t under git when it was opened in Neovim it will stay nil even if you add a .git later while it’s still open.
The solution is to restart Neovim, for example using :restart, or just reopen it.
Please don’t use AI :/

[echasnovski]

2. No re-attach loop is possible. auto_enable is gated on H.is_buf_enabled(buf_id) and fires only on BufEnter. After fail_attach, H.cache[buf_id] is nil (buffer disabled); nothing schedules another enable until the user switches to the buffer again — which is exactly when a retry is wanted (the user may have just run git init).

Retry on user switching to the buffer again is exactly when trying to re-attach is not wanted. Because it will lead to unlimited re-attach tries for files that are not in the Git repository.

The solution is to restart Neovim, for example using :restart, or just reopen it.

Although this would work, the intended solution is to explicitly :edit in the file. This causes detach and the re-attach. However, this works in 'mini.git' but not in 'mini.diff'. I'll take a look, this should be more or less straightforward.

But this PR is definitely not the wanted approach, sorry.