perf: pre-compile embedded Lua source into bytecode (#16631)

The Lua modules that make up vim.lua are embedded as raw source files into the
nvim binary. These sources are loaded by the Lua runtime on startuptime. We can
pre-compile these sources into Lua bytecode before embedding them into the
binary, which minimizes the size of the binary and improves startuptime.

CMakeLists.txt

@@ -543,6 +543,24 @@ endif()
 
 message(STATUS "Using Lua interpreter: ${LUA_PRG}")
 
+if(NOT WIN32)
+  if(PREFER_LUA)
+    foreach(CURRENT_LUAC_PRG luac5.1 luac)
+      find_program(_CHECK_LUAC_PRG ${CURRENT_LUAC_PRG})
+      if(_CHECK_LUAC_PRG)
+        set(LUAC_PRG "${_CHECK_LUAC_PRG} -s -o - %s" CACHE STRING "Format for compiling to Lua bytecode")
+        break()
+      endif()
+    endforeach()
+  elseif(LUA_PRG MATCHES "luajit")
+    set(LUAC_PRG "${LUA_PRG} -b -s %s -" CACHE STRING "Format for compiling to Lua bytecode")
+  endif()
+endif()
+
+if(LUAC_PRG)
+  message(STATUS "Using Lua compiler: ${LUAC_PRG}")
+endif()
+
 # Setup busted.
 find_program(BUSTED_PRG NAMES busted busted.bat)
 find_program(BUSTED_LUA_PRG busted-lua)

src/nvim/CMakeLists.txt

@@ -326,7 +326,9 @@ add_custom_command(
 
 add_custom_command(
   OUTPUT ${VIM_MODULE_FILE}
-  COMMAND ${LUA_PRG} ${CHAR_BLOB_GENERATOR} ${VIM_MODULE_FILE}
+  COMMAND ${CMAKE_COMMAND} -E env
+      "LUAC_PRG=${LUAC_PRG}"
+      ${LUA_PRG} ${CHAR_BLOB_GENERATOR} -c ${VIM_MODULE_FILE}
       ${LUA_VIM_MODULE_SOURCE} vim_module
       ${LUA_SHARED_MODULE_SOURCE} shared_module
       ${LUA_INSPECT_MODULE_SOURCE} inspect_module
@@ -339,6 +341,7 @@ add_custom_command(
     ${LUA_INSPECT_MODULE_SOURCE}
     ${LUA_F_MODULE_SOURCE}
     ${LUA_META_MODULE_SOURCE}
+  VERBATIM
 )
 
 list(APPEND NVIM_GENERATED_SOURCES

src/nvim/generators/gen_char_blob.lua

@@ -1,12 +1,26 @@
 if arg[1] == '--help' then
   print('Usage:')
-  print('  '..arg[0]..' target source varname [source varname]...')
+  print('  '..arg[0]..' [-c] target source varname [source varname]...')
   print('')
   print('Generates C file with big uint8_t blob.')
   print('Blob will be stored in a static const array named varname.')
   os.exit()
 end
 
+-- Recognized options:
+--   -c   compile Lua bytecode
+local options = {}
+
+while true do
+  local opt = string.match(arg[1], "^-(%w)")
+  if not opt then
+    break
+  end
+
+  options[opt] = true
+  table.remove(arg, 1)
+end
+
 assert(#arg >= 3 and (#arg - 1) % 2 == 0)
 
 local target_file = arg[1] or error('Need a target file')
@@ -23,11 +37,25 @@ for argi = 2, #arg, 2 do
   end
   varnames[varname] = source_file
 
-  local source = io.open(source_file, 'r')
-      or error(string.format("source_file %q doesn't exist", source_file))
-
   target:write(('static const uint8_t %s[] = {\n'):format(varname))
 
+  local output
+  if options.c then
+    local luac = os.getenv("LUAC_PRG")
+    if luac then
+      output = io.popen(luac:format(source_file), "r"):read("*a")
+    else
+      print("LUAC_PRG is undefined")
+    end
+  end
+
+  if not output then
+    local source = io.open(source_file, "r")
+        or error(string.format("source_file %q doesn't exist", source_file))
+    output = source:read("*a")
+    source:close()
+  end
+
   local num_bytes = 0
   local MAX_NUM_BYTES = 15  -- 78 / 5: maximum number of bytes on one line
   target:write(' ')
@@ -41,19 +69,13 @@ for argi = 2, #arg, 2 do
     end
   end
 
-  for line in source:lines() do
+  for i = 1, string.len(output) do
-    for i = 1, string.len(line) do
+    local byte = output:byte(i)
-      local byte = line:byte(i)
+    target:write(string.format(' %3u,', byte))
-      assert(byte ~= 0)
-      target:write(string.format(' %3u,', byte))
-      increase_num_bytes()
-    end
-    target:write(string.format(' %3u,', string.byte('\n', 1)))
     increase_num_bytes()
   end
 
-  target:write('   0};\n')
+  target:write('  0};\n')
-  source:close()
 end
 
 target:close()

src/nvim/lua/executor.c

@@ -404,9 +404,9 @@ static int nlua_state_init(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
 
   {
     const char *code = (char *)&shared_module[0];
-    if (luaL_loadbuffer(lstate, code, strlen(code), "@vim/shared.lua")
+    if (luaL_loadbuffer(lstate, code, sizeof(shared_module) - 1, "@vim/shared.lua")
         || nlua_pcall(lstate, 0, 0)) {
-      nlua_error(lstate, _("E5106: Error while creating shared module: %.*s"));
+      nlua_error(lstate, _("E5106: Error while creating shared module: %.*s\n"));
       return 1;
     }
   }
@@ -416,18 +416,18 @@ static int nlua_state_init(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
     lua_getfield(lstate, -1, "loaded");  // [package, loaded]
 
     const char *code = (char *)&inspect_module[0];
-    if (luaL_loadbuffer(lstate, code, strlen(code), "@vim/inspect.lua")
+    if (luaL_loadbuffer(lstate, code, sizeof(inspect_module) - 1, "@vim/inspect.lua")
         || nlua_pcall(lstate, 0, 1)) {
-      nlua_error(lstate, _("E5106: Error while creating inspect module: %.*s"));
+      nlua_error(lstate, _("E5106: Error while creating inspect module: %.*s\n"));
       return 1;
     }
     // [package, loaded, inspect]
     lua_setfield(lstate, -2, "vim.inspect");  // [package, loaded]
 
     code = (char *)&lua_F_module[0];
-    if (luaL_loadbuffer(lstate, code, strlen(code), "@vim/F.lua")
+    if (luaL_loadbuffer(lstate, code, sizeof(lua_F_module) - 1, "@vim/F.lua")
         || nlua_pcall(lstate, 0, 1)) {
-      nlua_error(lstate, _("E5106: Error while creating vim.F module: %.*s"));
+      nlua_error(lstate, _("E5106: Error while creating vim.F module: %.*s\n"));
       return 1;
     }
     // [package, loaded, module]
@@ -438,9 +438,9 @@ static int nlua_state_init(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
 
   {
     const char *code = (char *)&vim_module[0];
-    if (luaL_loadbuffer(lstate, code, strlen(code), "@vim.lua")
+    if (luaL_loadbuffer(lstate, code, sizeof(vim_module) - 1, "@vim.lua")
         || nlua_pcall(lstate, 0, 0)) {
-      nlua_error(lstate, _("E5106: Error while creating vim module: %.*s"));
+      nlua_error(lstate, _("E5106: Error while creating vim module: %.*s\n"));
       return 1;
     }
   }
@@ -450,9 +450,9 @@ static int nlua_state_init(lua_State *const lstate) FUNC_ATTR_NONNULL_ALL
     lua_getfield(lstate, -1, "loaded");  // [package, loaded]
 
     const char *code = (char *)&lua_meta_module[0];
-    if (luaL_loadbuffer(lstate, code, strlen(code), "@vim/_meta.lua")
+    if (luaL_loadbuffer(lstate, code, sizeof(lua_meta_module) - 1, "@vim/_meta.lua")
         || nlua_pcall(lstate, 0, 1)) {
-      nlua_error(lstate, _("E5106: Error while creating vim._meta module: %.*s"));
+      nlua_error(lstate, _("E5106: Error while creating vim._meta module: %.*s\n"));
       return 1;
     }
     // [package, loaded, module]

test/functional/lua/vim_spec.lua

@@ -131,9 +131,9 @@ describe('lua stdlib', function()
     eq(false, funcs.luaeval('vim.startswith("123", "2")'))
     eq(false, funcs.luaeval('vim.startswith("123", "1234")'))
 
-    eq("Error executing lua: vim/shared.lua:0: prefix: expected string, got nil",
+    matches("prefix: expected string, got nil",
       pcall_err(exec_lua, 'return vim.startswith("123", nil)'))
-    eq("Error executing lua: vim/shared.lua:0: s: expected string, got nil",
+    matches("s: expected string, got nil",
       pcall_err(exec_lua, 'return vim.startswith(nil, "123")'))
   end)
 
@@ -147,9 +147,9 @@ describe('lua stdlib', function()
     eq(false, funcs.luaeval('vim.endswith("123", "2")'))
     eq(false, funcs.luaeval('vim.endswith("123", "1234")'))
 
-    eq("Error executing lua: vim/shared.lua:0: suffix: expected string, got nil",
+    matches("suffix: expected string, got nil",
       pcall_err(exec_lua, 'return vim.endswith("123", nil)'))
-    eq("Error executing lua: vim/shared.lua:0: s: expected string, got nil",
+    matches("s: expected string, got nil",
       pcall_err(exec_lua, 'return vim.endswith(nil, "123")'))
   end)
 
@@ -220,9 +220,9 @@ describe('lua stdlib', function()
     eq({"yy","xx"}, exec_lua("return test_table"))
 
     -- Validates args.
-    eq('Error executing lua: vim.schedule: expected function',
+    matches('vim.schedule: expected function',
       pcall_err(exec_lua, "vim.schedule('stringly')"))
-    eq('Error executing lua: vim.schedule: expected function',
+    matches('vim.schedule: expected function',
       pcall_err(exec_lua, "vim.schedule()"))
 
     exec_lua([[
@@ -232,7 +232,7 @@ describe('lua stdlib', function()
     ]])
 
     feed("<cr>")
-    eq('Error executing vim.schedule lua callback: [string "<nvim>"]:2: big failure\nvery async', remove_trace(eval("v:errmsg")))
+    matches('big failure\nvery async', remove_trace(eval("v:errmsg")))
 
     local screen = Screen.new(60,5)
     screen:set_default_attr_ids({
@@ -300,16 +300,16 @@ describe('lua stdlib', function()
     }
 
     for _, t in ipairs(loops) do
-      eq("Error executing lua: vim/shared.lua:0: Infinite loop detected", pcall_err(split, t[1], t[2]))
+      matches("Infinite loop detected", pcall_err(split, t[1], t[2]))
     end
 
     -- Validates args.
     eq(true, pcall(split, 'string', 'string'))
-    eq('Error executing lua: vim/shared.lua:0: s: expected string, got number',
+    matches('s: expected string, got number',
       pcall_err(split, 1, 'string'))
-    eq('Error executing lua: vim/shared.lua:0: sep: expected string, got number',
+    matches('sep: expected string, got number',
       pcall_err(split, 'string', 1))
-    eq('Error executing lua: vim/shared.lua:0: kwargs: expected table, got number',
+    matches('kwargs: expected table, got number',
       pcall_err(split, 'string', 'string', 1))
   end)
 
@@ -330,7 +330,7 @@ describe('lua stdlib', function()
     end
 
     -- Validates args.
-    eq('Error executing lua: vim/shared.lua:0: s: expected string, got number',
+    matches('s: expected string, got number',
       pcall_err(trim, 2))
   end)
 
@@ -410,7 +410,7 @@ describe('lua stdlib', function()
       return getmetatable(t2) == mt
     ]]))
 
-    eq('Error executing lua: vim/shared.lua:0: Cannot deepcopy object of type thread',
+    matches('Cannot deepcopy object of type thread',
       pcall_err(exec_lua, [[
         local thread = coroutine.create(function () return 0 end)
         local t = {thr = thread}
@@ -423,7 +423,7 @@ describe('lua stdlib', function()
     eq('foo%%%-bar', exec_lua([[return vim.pesc(vim.pesc('foo-bar'))]]))
 
     -- Validates args.
-    eq('Error executing lua: vim/shared.lua:0: s: expected string, got number',
+    matches('s: expected string, got number',
       pcall_err(exec_lua, [[return vim.pesc(2)]]))
   end)
 
@@ -548,19 +548,19 @@ describe('lua stdlib', function()
       return c.x.a == 1 and c.x.b == 2 and c.x.c == nil and count == 1
     ]]))
 
-    eq('Error executing lua: vim/shared.lua:0: invalid "behavior": nil',
+    matches('invalid "behavior": nil',
       pcall_err(exec_lua, [[
         return vim.tbl_extend()
       ]])
     )
 
-    eq('Error executing lua: vim/shared.lua:0: wrong number of arguments (given 1, expected at least 3)',
+    matches('wrong number of arguments %(given 1, expected at least 3%)',
       pcall_err(exec_lua, [[
         return vim.tbl_extend("keep")
       ]])
     )
 
-    eq('Error executing lua: vim/shared.lua:0: wrong number of arguments (given 2, expected at least 3)',
+    matches('wrong number of arguments %(given 2, expected at least 3%)',
       pcall_err(exec_lua, [[
         return vim.tbl_extend("keep", {})
       ]])
@@ -661,19 +661,19 @@ describe('lua stdlib', function()
       return vim.tbl_deep_extend("force", a, b)
     ]]), {a = 123 })
 
-    eq('Error executing lua: vim/shared.lua:0: invalid "behavior": nil',
+    matches('invalid "behavior": nil',
       pcall_err(exec_lua, [[
         return vim.tbl_deep_extend()
       ]])
     )
 
-    eq('Error executing lua: vim/shared.lua:0: wrong number of arguments (given 1, expected at least 3)',
+    matches('wrong number of arguments %(given 1, expected at least 3%)',
       pcall_err(exec_lua, [[
         return vim.tbl_deep_extend("keep")
       ]])
     )
 
-    eq('Error executing lua: vim/shared.lua:0: wrong number of arguments (given 2, expected at least 3)',
+    matches('wrong number of arguments %(given 2, expected at least 3%)',
       pcall_err(exec_lua, [[
         return vim.tbl_deep_extend("keep", {})
       ]])
@@ -706,7 +706,7 @@ describe('lua stdlib', function()
 
   it('vim.list_extend', function()
     eq({1,2,3}, exec_lua [[ return vim.list_extend({1}, {2,3}) ]])
-    eq('Error executing lua: vim/shared.lua:0: src: expected table, got nil',
+    matches('src: expected table, got nil',
       pcall_err(exec_lua, [[ return vim.list_extend({1}, nil) ]]))
     eq({1,2}, exec_lua [[ return vim.list_extend({1}, {2;a=1}) ]])
     eq(true, exec_lua [[ local a = {1} return vim.list_extend(a, {2;a=1}) == a ]])
@@ -730,7 +730,7 @@ describe('lua stdlib', function()
     assert(vim.deep_equal(a, { A = 1; [1] = 'A'; }))
     vim.tbl_add_reverse_lookup(a)
     ]]
-    matches('^Error executing lua: vim/shared%.lua:0: The reverse lookup found an existing value for "[1A]" while processing key "[1A]"$',
+    matches('The reverse lookup found an existing value for "[1A]" while processing key "[1A]"$',
       pcall_err(exec_lua, code))
   end)
 
@@ -771,7 +771,7 @@ describe('lua stdlib', function()
   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',
+      matches('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)
 
@@ -907,37 +907,37 @@ describe('lua stdlib', function()
     exec_lua("vim.validate{arg1={{}, 't' }, arg2={ 'foo', 's' }}")
     exec_lua("vim.validate{arg1={2, function(a) return (a % 2) == 0  end, 'even number' }}")
 
-    eq('Error executing lua: [string "<nvim>"]:0: opt[1]: expected table, got number',
+    matches('expected table, got number',
       pcall_err(exec_lua, "vim.validate{ 1, 'x' }"))
-    eq('Error executing lua: [string "<nvim>"]:0: invalid type name: x',
+    matches('invalid type name: x',
       pcall_err(exec_lua, "vim.validate{ arg1={ 1, 'x' }}"))
-    eq('Error executing lua: [string "<nvim>"]:0: invalid type name: 1',
+    matches('invalid type name: 1',
       pcall_err(exec_lua, "vim.validate{ arg1={ 1, 1 }}"))
-    eq('Error executing lua: [string "<nvim>"]:0: invalid type name: nil',
+    matches('invalid type name: nil',
       pcall_err(exec_lua, "vim.validate{ arg1={ 1 }}"))
 
     -- Validated parameters are required by default.
-    eq('Error executing lua: [string "<nvim>"]:0: arg1: expected string, got nil',
+    matches('arg1: expected string, got nil',
       pcall_err(exec_lua, "vim.validate{ arg1={ nil, 's' }}"))
     -- Explicitly required.
-    eq('Error executing lua: [string "<nvim>"]:0: arg1: expected string, got nil',
+    matches('arg1: expected string, got nil',
       pcall_err(exec_lua, "vim.validate{ arg1={ nil, 's', false }}"))
 
-    eq('Error executing lua: [string "<nvim>"]:0: arg1: expected table, got number',
+    matches('arg1: expected table, got number',
       pcall_err(exec_lua, "vim.validate{arg1={1, 't'}}"))
-    eq('Error executing lua: [string "<nvim>"]:0: arg2: expected string, got number',
+    matches('arg2: expected string, got number',
       pcall_err(exec_lua, "vim.validate{arg1={{}, 't'}, arg2={1, 's'}}"))
-    eq('Error executing lua: [string "<nvim>"]:0: arg2: expected string, got nil',
+    matches('arg2: expected string, got nil',
       pcall_err(exec_lua, "vim.validate{arg1={{}, 't'}, arg2={nil, 's'}}"))
-    eq('Error executing lua: [string "<nvim>"]:0: arg2: expected string, got nil',
+    matches('arg2: expected string, got nil',
       pcall_err(exec_lua, "vim.validate{arg1={{}, 't'}, arg2={nil, 's'}}"))
-    eq('Error executing lua: [string "<nvim>"]:0: arg1: expected even number, got 3',
+    matches('arg1: expected even number, got 3',
       pcall_err(exec_lua, "vim.validate{arg1={3, function(a) return a == 1 end, 'even number'}}"))
-    eq('Error executing lua: [string "<nvim>"]:0: arg1: expected ?, got 3',
+    matches('arg1: expected %?, got 3',
       pcall_err(exec_lua, "vim.validate{arg1={3, function(a) return a == 1 end}}"))
 
     -- Pass an additional message back.
-    eq('Error executing lua: [string "<nvim>"]:0: arg1: expected ?, got 3. Info: TEST_MSG',
+    matches('arg1: expected %?, got 3. Info: TEST_MSG',
       pcall_err(exec_lua, "vim.validate{arg1={3, function(a) return a == 1, 'TEST_MSG' end}}"))
   end)
 
@@ -982,7 +982,7 @@ describe('lua stdlib', function()
     ]]
     eq(NIL, funcs.luaeval "vim.g.to_delete")
 
-    matches([[^Error executing lua: .*: attempt to index .* nil value]],
+    matches([[attempt to index .* nil value]],
        pcall_err(exec_lua, 'return vim.g[0].testing'))
   end)
 
@@ -1009,7 +1009,7 @@ describe('lua stdlib', function()
       return {vim.b.nonexistant == vim.NIL, vim.b.nullvar == vim.NIL}
     ]])
 
-    matches([[^Error executing lua: .*: attempt to index .* nil value]],
+    matches([[attempt to index .* nil value]],
        pcall_err(exec_lua, 'return vim.b[BUF][0].testing'))
 
     eq({hello="world"}, funcs.luaeval "vim.b.to_delete")
@@ -1046,7 +1046,7 @@ describe('lua stdlib', function()
     eq(NIL, funcs.luaeval "vim.w.nonexistant")
     eq(NIL, funcs.luaeval "vim.w[WIN].nonexistant")
 
-    matches([[^Error executing lua: .*: attempt to index .* nil value]],
+    matches([[attempt to index .* nil value]],
        pcall_err(exec_lua, 'return vim.w[WIN][0].testing'))
 
     eq({hello="world"}, funcs.luaeval "vim.w.to_delete")
@@ -1078,7 +1078,7 @@ describe('lua stdlib', function()
     eq(123, funcs.luaeval "vim.t[0].other")
     eq(NIL, funcs.luaeval "vim.t[0].nonexistant")
 
-    matches([[^Error executing lua: .*: attempt to index .* nil value]],
+    matches([[attempt to index .* nil value]],
        pcall_err(exec_lua, 'return vim.t[0][0].testing'))
 
     eq({hello="world"}, funcs.luaeval "vim.t.to_delete")
@@ -1108,7 +1108,7 @@ describe('lua stdlib', function()
     eq(funcs.luaeval "vim.api.nvim_get_vvar('progpath')", funcs.luaeval "vim.v.progpath")
     eq(false, funcs.luaeval "vim.v['false']")
     eq(NIL, funcs.luaeval "vim.v.null")
-    matches([[^Error executing lua: .*: attempt to index .* nil value]],
+    matches([[attempt to index .* nil value]],
        pcall_err(exec_lua, 'return vim.v[0].progpath'))
   end)
 
@@ -1128,9 +1128,9 @@ describe('lua stdlib', function()
     ]]
     eq('', funcs.luaeval "vim.bo.filetype")
     eq(true, funcs.luaeval "vim.bo[BUF].modifiable")
-    matches("^Error executing lua: .*: Invalid option name: 'nosuchopt'$",
+    matches("Invalid option name: 'nosuchopt'$",
        pcall_err(exec_lua, 'return vim.bo.nosuchopt'))
-    matches("^Error executing lua: .*: Expected lua string$",
+    matches("Expected lua string$",
        pcall_err(exec_lua, 'return vim.bo[0][0].autoread'))
   end)
 
@@ -1147,9 +1147,9 @@ describe('lua stdlib', function()
     eq(0, funcs.luaeval "vim.wo.cole")
     eq(0, funcs.luaeval "vim.wo[0].cole")
     eq(0, funcs.luaeval "vim.wo[1001].cole")
-    matches("^Error executing lua: .*: Invalid option name: 'notanopt'$",
+    matches("Invalid option name: 'notanopt'$",
        pcall_err(exec_lua, 'return vim.wo.notanopt'))
-    matches("^Error executing lua: .*: Expected lua string$",
+    matches("Expected lua string$",
        pcall_err(exec_lua, 'return vim.wo[0][0].list'))
     eq(2, funcs.luaeval "vim.wo[1000].cole")
     exec_lua [[

test/functional/terminal/tui_spec.lua

@@ -20,6 +20,7 @@ local nvim_prog = helpers.nvim_prog
 local nvim_set = helpers.nvim_set
 local ok = helpers.ok
 local read_file = helpers.read_file
+local exec_lua = helpers.exec_lua
 
 if helpers.pending_win32(pending) then return end
 
@@ -580,21 +581,34 @@ describe('TUI', function()
   end)
 
   it("paste: 'nomodifiable' buffer", function()
+    local has_luajit = exec_lua('return jit ~= nil')
     child_session:request('nvim_command', 'set nomodifiable')
     child_session:request('nvim_exec_lua', [[
       -- Stack traces for this test are non-deterministic, so disable them
       _G.debug.traceback = function(msg) return msg end
     ]], {})
     feed_data('\027[200~fail 1\nfail 2\n\027[201~')
-    screen:expect{grid=[[
+    if has_luajit then
-                                                        |
+      screen:expect{grid=[[
-      {4:~                                                 }|
+                                                          |
-      {5:                                                  }|
+        {4:~                                                 }|
-      {8:paste: Error executing lua: vim.lua:243: Vim:E21: }|
+        {5:                                                  }|
-      {8:Cannot make changes, 'modifiable' is off}          |
+        {8:paste: Error executing lua: vim.lua:0: Vim:E21: Ca}|
-      {10:Press ENTER or type command to continue}{1: }          |
+        {8:nnot make changes, 'modifiable' is off}            |
-      {3:-- TERMINAL --}                                    |
+        {10:Press ENTER or type command to continue}{1: }          |
-    ]]}
+        {3:-- TERMINAL --}                                    |
+      ]]}
+    else
+      screen:expect{grid=[[
+                                                          |
+        {4:~                                                 }|
+        {5:                                                  }|
+        {8:paste: Error executing lua: Vim:E21: Cannot make c}|
+        {8:hanges, 'modifiable' is off}                       |
+        {10:Press ENTER or type command to continue}{1: }          |
+        {3:-- TERMINAL --}                                    |
+      ]]}
+    end
     feed_data('\n')  -- <Enter>
     child_session:request('nvim_command', 'set modifiable')
     feed_data('\027[200~success 1\nsuccess 2\n\027[201~')