fix(file): Handle race condition during buffer creation

(rel. sindrets#392)

Author: sindrets

lua/diffview/scene/window.lua

@@ -92,12 +92,16 @@ end
 Window.load_file = async.wrap(function(self, callback)
   assert(self.file)
 
-  if self.file.bufnr and api.nvim_buf_is_valid(self.file.bufnr) then
-    return callback(true)
-  end
+  if self.file:is_valid() then return callback(true) end
 
   local ok, err = pawait(self.file.create_buffer, self.file)
 
+  if ok and not self.file:is_valid() then
+    -- The buffer may have been destroyed during the await
+    ok = false
+    err = "The file buffer is invalid!"
+  end
+
   if not ok then
     logger:error(err)
     utils.err(fmt("Failed to create diff buffer: '%s:%s'", self.file.rev, self.file.path), true)

lua/diffview/vcs/file.lua

@@ -255,7 +255,10 @@ File.create_buffer = async.wrap(function(self, callback)
 
   -- Revalidate buffer in case the file was destroyed before `produce_data()`
   -- returned.
-  if not api.nvim_buf_is_valid(self.bufnr) then return end
+  if not api.nvim_buf_is_valid(self.bufnr) then
+    error("The buffer has been invalidated!")
+    return
+  end
   local bufopts = vim.deepcopy(File.bufopts)
 
   if self.rev.type == RevType.STAGE and self.rev.stage == 0 then