refactor(git): scratch buffers wipe by default, consolidate factories in util

lua/git/util.lua

@@ -44,6 +44,44 @@ function M.parse_revspec(revspec)
     return { stage = nil, path = path }
 end
 
+---@class ow.Git.ScratchOpts
+---@field name string?
+---@field bufhidden ("hide"|"wipe")?  defaults to "wipe"
+
+---Configure a fresh buffer as a read-only scratch and optionally name
+---it. Shared by `empty_buf` and `new_scratch`; the public functions
+---differ in whether they dedup-by-name or place the buffer in a window.
+---@param buf integer
+---@param opts ow.Git.ScratchOpts
+local function setup_scratch(buf, opts)
+    vim.bo[buf].buftype = "nofile"
+    vim.bo[buf].bufhidden = opts.bufhidden or "wipe"
+    vim.bo[buf].swapfile = false
+    vim.bo[buf].modifiable = false
+    vim.bo[buf].modified = false
+    if opts.name then
+        pcall(vim.api.nvim_buf_set_name, buf, opts.name)
+    end
+end
+
+---Build a read-only scratch buffer, optionally naming it. When `opts.name`
+---is set and a loaded buffer with that name already exists, returns it
+---instead of creating a duplicate.
+---@param opts ow.Git.ScratchOpts?
+---@return integer
+function M.empty_buf(opts)
+    opts = opts or {}
+    if opts.name then
+        local existing = vim.fn.bufnr(opts.name)
+        if existing ~= -1 and vim.api.nvim_buf_is_loaded(existing) then
+            return existing
+        end
+    end
+    local buf = vim.api.nvim_create_buf(false, true)
+    setup_scratch(buf, opts)
+    return buf
+end
+
 ---Place a buffer in the current window or a new split per `split`.
 ---`false` replaces the current buffer (drops a `'` mark first so `''`
 ---jumps back); a direction string opens a leftabove split; nil falls
@@ -62,12 +100,10 @@ function M.place_buf(buf, split)
     })
 end
 
----@class ow.Git.NewScratchOpts
----@field name string?
----@field bufhidden ("hide"|"wipe")?  defaults to "hide"
+---@class ow.Git.NewScratchOpts : ow.Git.ScratchOpts
 ---@field split (false|"above"|"below"|"left"|"right")? defaults to splitbelow-aware horizontal. `false` places the buffer in the current window (drops a `'` mark first so the user can jump back).
 
----Create a fresh non-modifiable scratch buffer and place it. Default split
+---Create a fresh read-only scratch buffer and place it. Default split
 ---direction is horizontal, honouring `splitbelow`. Caller flips
 ---`modifiable`, fills the buffer, and sets `filetype` once content lands.
 ---@param opts ow.Git.NewScratchOpts?
@@ -76,14 +112,7 @@ end
 function M.new_scratch(opts)
     opts = opts or {}
     local buf = vim.api.nvim_create_buf(false, true)
-    vim.bo[buf].buftype = "nofile"
-    vim.bo[buf].bufhidden = opts.bufhidden or "hide"
-    vim.bo[buf].swapfile = false
-    vim.bo[buf].modifiable = false
-    vim.bo[buf].modified = false
-    if opts.name then
-        pcall(vim.api.nvim_buf_set_name, buf, opts.name)
-    end
+    setup_scratch(buf, opts)
     return buf, M.place_buf(buf, opts.split)
 end