refactor(git): promote set_buf_name_and_filetype to diff.M

lua/git/diff.lua

@@ -145,9 +145,13 @@ function M.load_file_buf(abs_path)
     return buf
 end
 
+---Name a scratch buffer with a `git://...` URI and apply the filetype
+---inferred from the inner path segment. The `nvim_buf_set_name` call is
+---wrapped in pcall because a buffer with that name may already exist
+---(E95).
 ---@param buf integer
 ---@param name string
-local function set_buf_name_and_filetype(buf, name)
+function M.set_buf_name_and_filetype(buf, name)
     pcall(vim.api.nvim_buf_set_name, buf, name)
     local ft = vim.filetype.match({ buf = buf })
     if ft then
@@ -181,7 +185,7 @@ function M.split(opts)
     local is_index = opts.ref == ""
     local other = M.git_show_buf(worktree, opts.ref, rel, is_index)
     local label = is_index and "index" or opts.ref
-    set_buf_name_and_filetype(other, "git://" .. label .. "/" .. rel)
+    M.set_buf_name_and_filetype(other, "git://" .. label .. "/" .. rel)
 
     local split_cmd = opts.vertical and "leftabove vertical sbuffer "
         or "leftabove sbuffer "

lua/git/show.lua

@@ -94,11 +94,7 @@ local function blob_buf(worktree, blob, path, ref)
     end
     ---@cast blob string
     local buf = diff.git_show_blob(worktree, blob)
-    pcall(vim.api.nvim_buf_set_name, buf, "git://" .. ref .. "/" .. path)
-    local ft = vim.filetype.match({ buf = buf })
-    if ft then
-        vim.bo[buf].filetype = ft
-    end
+    diff.set_buf_name_and_filetype(buf, "git://" .. ref .. "/" .. path)
     return buf
 end
 

lua/git/status_win.lua

@@ -620,11 +620,7 @@ local function show_diff(s, entry, focus_left)
     vim.api.nvim_win_set_buf(right_win, pair.right.buf)
     for _, side in ipairs({ pair.left, pair.right }) do
         if side.name then
-            pcall(vim.api.nvim_buf_set_name, side.buf, side.name)
-            local ft = vim.filetype.match({ buf = side.buf })
-            if ft then
-                vim.bo[side.buf].filetype = ft
-            end
+            diff.set_buf_name_and_filetype(side.buf, side.name)
         end
     end
     set_diff(left_win, true)