fix(lua): show stacktrace for error in vim.on_key() callback (#31021)

runtime/lua/vim/_editor.lua

@@ -701,11 +701,13 @@ end
 --- Executes the on_key callbacks.
 ---@private
 function vim._on_key(buf, typed_buf)
-  local failed_ns_ids = {}
-  local failed_messages = {}
+  local failed = {} ---@type [integer, string][]
   local discard = false
   for k, v in pairs(on_key_cbs) do
-    local ok, rv = pcall(v[1], buf, typed_buf)
+    local fn = v[1]
+    local ok, rv = xpcall(function()
+      return fn(buf, typed_buf)
+    end, debug.traceback)
     if ok and rv ~= nil then
       if type(rv) == 'string' and #rv == 0 then
         discard = true
@@ -718,19 +720,16 @@ function vim._on_key(buf, typed_buf)
     end
     if not ok then
       vim.on_key(nil, k)
-      table.insert(failed_ns_ids, k)
-      table.insert(failed_messages, rv)
+      table.insert(failed, { k, rv })
     end
   end
 
-  if failed_ns_ids[1] then
-    error(
-      string.format(
-        "Error executing 'on_key' with ns_ids '%s'\n    Messages: %s",
-        table.concat(failed_ns_ids, ', '),
-        table.concat(failed_messages, '\n')
-      )
-    )
+  if #failed > 0 then
+    local errmsg = ''
+    for _, v in ipairs(failed) do
+      errmsg = errmsg .. string.format('\nWith ns_id %d: %s', v[1], v[2])
+    end
+    error(errmsg)
   end
   return discard
 end

src/nvim/lua/executor.c

@@ -2099,9 +2099,9 @@ bool nlua_execute_on_key(int c, char *typed_buf)
   int save_got_int = got_int;
   got_int = false;  // avoid interrupts when the key typed is Ctrl-C
   bool discard = false;
-  if (nlua_pcall(lstate, 2, 1)) {
-    nlua_error(lstate,
-               _("Error executing  vim.on_key Lua callback: %.*s"));
+  // Do not use nlua_pcall here to avoid duplicate stack trace information
+  if (lua_pcall(lstate, 2, 1, 0)) {
+    nlua_error(lstate, _("Error executing vim.on_key() callbacks: %.*s"));
   } else {
     if (lua_isboolean(lstate, -1)) {
       discard = lua_toboolean(lstate, -1);

test/functional/lua/vim_spec.lua

@@ -3312,10 +3312,17 @@ describe('lua stdlib', function()
       eq('inext lines<ESC>', exec_lua [[return table.concat(keys, '')]])
     end)
 
-    it('skips any function that caused an error', function()
+    it('skips any function that caused an error and shows stacktrace', function()
       insert([[hello world]])
 
       exec_lua [[
+        local function ErrF2()
+          error("Dumb Error")
+        end
+        local function ErrF1()
+          ErrF2()
+        end
+
         keys = {}
 
         return vim.on_key(function(buf)
@@ -3326,7 +3333,7 @@ describe('lua stdlib', function()
           table.insert(keys, buf)
 
           if buf == 'l' then
-            error("Dumb Error")
+            ErrF1()
           end
         end)
       ]]
@@ -3336,6 +3343,19 @@ describe('lua stdlib', function()
 
       -- Only the first letter gets added. After that we remove the callback
       eq('inext l', exec_lua [[ return table.concat(keys, '') ]])
+
+      local errmsg = api.nvim_get_vvar('errmsg')
+      matches(
+        [[
+^Error executing vim%.on%_key%(%) callbacks:.*
+With ns%_id %d+: .*: Dumb Error
+stack traceback:
+.*: in function 'error'
+.*: in function 'ErrF2'
+.*: in function 'ErrF1'
+.*]],
+        errmsg
+      )
     end)
 
     it('argument 1 is keys after mapping, argument 2 is typed keys', function()
@@ -3449,6 +3469,7 @@ describe('lua stdlib', function()
       -- second key produces an error which removes the callback
       exec_lua [[
         n_call = 0
+
         vim.on_key(function(buf, typed_buf)
           if typed_buf == 'x' then
             n_call = n_call + 1
@@ -3460,7 +3481,7 @@ describe('lua stdlib', function()
       api.nvim_buf_set_lines(0, 0, -1, true, { '54321' })
 
       local function cleanup_msg(msg)
-        return (remove_trace(msg):gsub('^Error.*\n *Messages: ', ''))
+        return msg:gsub('^Error .*\nWith ns%_id %d+: ', '')
       end
 
       feed('x')