From ec27f2b02813eceff156db32101442ef1c1b57ed Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tautvydas=20S=CC=8Cidlauskas?=
 <tautvydas.sidlauskas@gmail.com>
Date: Thu, 6 Aug 2026 14:44:39 +0300
Subject: [PATCH] fix(lsp): attach dartls to the buffer that requested it

`M.attach()` validates the path of the current buffer, but
`vim.lsp.start()` was called without `opts`, so the client attached to
whichever buffer happened to be current when the callback ran. With
`flutter_lookup_cmd` configured that callback is scheduled off a job's
output, so switching buffers right after opening a dart file attached
dartls to the wrong buffer and left the dart file unattached.

Pass the captured `bufnr` through, and bail out if the buffer is gone by
the time the callback runs.

Also cache the paths resolved via `flutter_lookup_cmd`, matching the
`fvm` and `flutter_path` branches. That branch was the only one leaving
`cached_paths` unset, so it re-ran the external lookup command on every
`attach()` - now once per `FileType` event since #527.
---
 lua/flutter-tools/executable.lua | 4 ++--
 lua/flutter-tools/lsp/init.lua   | 5 ++++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/lua/flutter-tools/executable.lua b/lua/flutter-tools/executable.lua
index 48f3de4f..1f74f844 100644
--- a/lua/flutter-tools/executable.lua
+++ b/lua/flutter-tools/executable.lua
@@ -174,13 +174,13 @@ function M.get(callback)
 
   if config.flutter_lookup_cmd then
     return path_from_lookup_cmd(config.flutter_lookup_cmd, function(paths)
-      paths = {
+      cached_paths = {
         flutter_bin = paths.flutter_bin,
         flutter_sdk = paths.flutter_sdk,
         dart_bin = paths.dart_bin,
         dart_sdk = dart_sdk_root(paths),
       }
-      callback(paths)
+      callback(cached_paths)
     end)
   end
 
diff --git a/lua/flutter-tools/lsp/init.lua b/lua/flutter-tools/lsp/init.lua
index 2f5e7dd4..e95672d5 100644
--- a/lua/flutter-tools/lsp/init.lua
+++ b/lua/flutter-tools/lsp/init.lua
@@ -287,12 +287,15 @@ function M.attach()
   if not is_valid_path(buffer_path) then return end
 
   get_server_config(user_config, function(c)
+    -- This callback can run asynchronously, by which point the user may have
+    -- switched to or deleted the buffer we were asked to attach to.
+    if not api.nvim_buf_is_valid(buf) then return end
     c.root_dir = M.get_project_root_dir()
       or fs.dirname(fs.find(conf.root_patterns, {
         path = buffer_path,
         upward = true,
       })[1])
-    vim.lsp.start(c)
+    vim.lsp.start(c, { bufnr = buf })
   end)
 end