refactor(git): unify absent-side handling in commit views

lua/git/object.lua

@@ -275,22 +275,16 @@ function M.read_uri(buf)
     vim.api.nvim_exec_autocmds("BufReadPost", { buffer = buf })
 end
 
----Buffer for the file at `<ref>:<path>`. A zero/nil blob (file absent
----on this side of the diff) maps to `/dev/null`, mirroring git's diff
----headers.
+---Buffer for the file at `<ref>:<path>`. Returns nil for a zero/nil
+---blob (file absent on this side of the diff).
 ---@param worktree string
 ---@param blob string?
 ---@param path string
 ---@param ref string  the commit ref the blob represents (e.g. `<sha>` or `<sha>^`)
----@return integer
+---@return integer?
 local function blob_buf(worktree, blob, path, ref)
     if is_zero(blob) then
-        local buf = vim.fn.bufnr("/dev/null")
-        if buf == -1 then
-            buf = vim.api.nvim_create_buf(true, true)
-            pcall(vim.api.nvim_buf_set_name, buf, "/dev/null")
-        end
-        return buf
+        return nil
     end
     return M.buf_for(worktree, ref .. ":" .. path)
 end
@@ -301,6 +295,10 @@ end
 ---@param ref string
 local function load_blob(worktree, blob, path, ref)
     local buf = blob_buf(worktree, blob, path, ref)
+    if not buf then
+        util.warning("no content for %s at %s", path, ref)
+        return
+    end
     vim.cmd.normal({ "m'", bang = true })
     vim.api.nvim_set_current_buf(buf)
 end
@@ -317,7 +315,18 @@ local function open_section(ctx, section)
         blob_buf(ctx.worktree, section.pre_blob, section.pre_path, parent)
     local right =
         blob_buf(ctx.worktree, section.post_blob, section.post_path, ctx.ref)
+    if left and right then
         diff.open(left, right, true)
+        return
+    end
+    if not left and not right then
+        util.warning("no content for %s", section.post_path)
+        return
+    end
+    local buf = left or right
+    ---@cast buf -nil
+    vim.cmd.normal({ "m'", bang = true })
+    vim.api.nvim_set_current_buf(buf)
 end
 
 ---@class ow.Git.OpenObjectOpts