Merge pull request #13875 from smolck/vim_fn_error_on_api

vim.fn: throw error when trying to use API function

src/nvim/lua/vim.lua

@@ -263,9 +263,16 @@ end
 -- vim.fn.{func}(...)
 vim.fn = setmetatable({}, {
   __index = function(t, key)
-    local function _fn(...)
+    local _fn
+    if vim.api[key] ~= nil then
+      _fn = function()
+        error(string.format("Tried to call API function with vim.fn: use vim.api.%s instead", key))
+      end
+    else
+      _fn = function(...)
         return vim.call(key, ...)
       end
+    end
     t[key] = _fn
     return _fn
   end

test/functional/lua/vim_spec.lua

@@ -715,6 +715,11 @@ describe('lua stdlib', function()
     eq({false, 'Vim:E714: List required'}, exec_lua([[return {pcall(vim.fn.add, "aa", "bb")}]]))
   end)
 
+  it('vim.fn should error when calling API function', function()
+      eq('Error executing lua: vim.lua:0: Tried to call API function with vim.fn: use vim.api.nvim_get_current_line instead',
+          pcall_err(exec_lua, "vim.fn.nvim_get_current_line()"))
+  end)
+
   it('vim.rpcrequest and vim.rpcnotify', function()
     exec_lua([[
       chan = vim.fn.jobstart({'cat'}, {rpc=true})