From d34cfe1cb83ad839001a9c5dc8ef588686ca2ff9 Mon Sep 17 00:00:00 2001
From: "Justin M. Keyes" <justinkz@gmail.com>
Date: Sun, 14 Jun 2026 20:20:45 +0200
Subject: [PATCH] fix(autoread): handle autocmd errors
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Problem:
Any random ftplugin or other autocmd, can throw an error when
`:checktime` reloads a buffer. This causes a trace which makes it look
like an issue with `autoread.lua`.

    vim.schedule callback: …/runtime/lua/nvim/autoread.lua:146:
    FileType Autocommands for "*"..function <SNR>1_LoadFTPlugin[20] ..script
    …/runtime/ftplugin/help.lua: Vim(runtime):E5113: Lua chunk:
    …/runtime/lua/vim/treesitter.lua:216: Index out of bounds
    stack traceback:
    [C]: in function 'nvim_buf_get_text'
    …/runtime/lua/vim/treesitter.lua:216: in function 'get_node_text'
    …/runtime/lua/vim/treesitter/query.lua:558: in function 'handler'
    …/runtime/lua/vim/treesitter/query.lua:843: in function '_match_predicates'
    …/runtime/lua/vim/treesitter/query.lua:1082: in function '(for generator)'
    …/runtime/ftplugin/help.lua:91: in function 'runnables'
    …/runtime/ftplugin/help.lua:124: in main chunk
    [C]: in function 'checktime'
    …/runtime/lua/nvim/autoread.lua:146: in function <…/runtime/lua/nvim/autoread.lua:138>

Solution:
Use pcall() and surface the error via nvim_echo.
---
 runtime/lua/nvim/autoread.lua             |  8 +++++++-
 test/functional/options/autoread_spec.lua | 20 ++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/runtime/lua/nvim/autoread.lua b/runtime/lua/nvim/autoread.lua
index 2691e8ccc2..5016c43f03 100644
--- a/runtime/lua/nvim/autoread.lua
+++ b/runtime/lua/nvim/autoread.lua
@@ -140,13 +140,19 @@ local function ensure_watcher(bufnr)
           set_pending(bufnr, false)
           return
         end
-        vim.cmd.checktime(bufnr)
+        -- Use pcall: autocmds (e.g. ftplugin) may throw during reload for any reason.
+        local ok, err = pcall(vim.cmd.checktime, bufnr) ---@type any, any
         set_pending(bufnr, false)
         -- On rename events (e.g. atomic save by another editor), the watcher
         -- is now stale (watching the old inode). Re-establish it.
         if change_type ~= watch.FileChangeType.Changed then
           ensure_watcher(bufnr)
         end
+        if not ok then
+          vim.api.nvim_echo({
+            { ('autoread: :checktime failed for buffer %d: %s'):format(bufnr, err) },
+          }, true, { err = true })
+        end
       end)
     end)
   end)
diff --git a/test/functional/options/autoread_spec.lua b/test/functional/options/autoread_spec.lua
index ad9bc13d2c..d3c7ab2052 100644
--- a/test/functional/options/autoread_spec.lua
+++ b/test/functional/options/autoread_spec.lua
@@ -199,6 +199,26 @@ describe('autoread file watcher', function()
     end)
   end)
 
+  it('handles autocmd error during reload', function()
+    local path = open_watched('original\n')
+    local bufnr = api.nvim_get_current_buf()
+
+    -- Define a broken autocmd.
+    n.exec_lua([[
+      vim.api.nvim_create_autocmd('FileChangedShellPost', {
+        callback = function() error('boom from test autocmd') end,
+      })
+    ]])
+
+    write_file(path, 'changed\n')
+
+    -- autoread should surface the error, and do its cleanup despite the failed autocmd.
+    retry(nil, 3000, function()
+      t.matches('autoread:.*boom from test autocmd', n.eval('v:errmsg'))
+      eq(0, api.nvim_get_option_value('busy', { buf = bufnr }))
+    end)
+  end)
+
   it('detects changes after atomic rename (external editor save)', function()
     local path = open_watched('original\n')