Improve luatest auto-requiring in Server:exec

In the commit 58eae75 auto-requiring of the 'luatest'
lib was added to the `Server:eval()` function, so it was also available
in `Server:exec()`, and it was defined as `t` variable. In the process
of development we found that the following construction doesn't work due
to the upvalue error:

    -- foo_bar_test.lua
    local t = require('luatest')

    ...
    g.test_foo_bar = function()
        server:exec(function()
            t.assert_equals(1, 1)  -- upvalues exception (!)
        end)
    end

To fix this error we decided to make the global variable `t` that had
the 'luatest' lib already loaded. So there was no need to import the
'luatest' lib in the test files and the following example worked:

    -- foo_bar_test.lua
    -- local t = require('luatest')  -- `t` is already defined

    ...
    g.test_foo_bar = function()
        server:exec(function()
            t.assert_equals(1, 1)  -- it works
        end)
    end:

But such an approach is not explicit enough and may mislead developers.
So it was decided to improve and extend the existing mechanism. Now we
just make the needed upvalue with the 'luatest' lib inside available in
the `Server:exec()` function via some magic. And now we can do something
like this:

    -- foo_bar_test.lua
    local t1 = require('luatest')
    local t2 = require('luatest')

    ...
    g.test_foo_bar_1 = function()
        server:exec(function()
            t1.assert_equals(1, 1)  -- it works
        end)
    end

    g.test_foo_bar_2 = function()
        server:exec(function()
            t2.assert_equals(1, 1)  -- it works
        end)
    end

Unfortunately, we cannot do the same for the `Server:eval()` function
and now it becomes just a shortcut for `Server.net_box:eval()` as it
was before the first version of auto-requiring of the 'luatest' lib.

Follows up #277
In scope of #233

Author: ylobankov

.luacheckrc

@@ -1,6 +1,4 @@
 include_files = {"**/*.lua", "*.rockspec", "*.luacheckrc"}
 exclude_files = {"lua_modules/", ".luarocks/", ".rocks/", "tmp/"}
 
-globals = {"t"}
-
 max_line_length = 120

CHANGELOG.md

@@ -41,7 +41,8 @@
 - Print Tarantool version used by luatest.
 - Add new module `replica_proxy.lua`.
 - Add new module `tarantool.lua`.
-- Autorequire `luatest` module in the server instance as `t` variable.
+- Auto-require `luatest` module in `Server:exec()` function where it is available
+  via the corresponding upvalue.
 
 ## 0.5.7
 

luatest/init.lua

@@ -95,8 +95,4 @@ function luatest.defaults(...)
     return luatest.configure(...)
 end
 
-if not rawget(_G, 't') then
-    rawset(_G, 't', luatest)
-end
-
 return luatest

luatest/server.lua

@@ -472,25 +472,15 @@ end
 
 --- Evaluate Lua code on the server.
 --
--- This is a wrapper for `server.net_box:eval()`.
+-- This is a shortcut for `server.net_box:eval()`.
 -- @string code
 -- @tab[opt] args
 -- @tab[opt] options
 function Server:eval(code, ...)
     if self.net_box == nil then
         error('net_box is not connected', 2)
     end
-    local preamble = [[
-        if not rawget(_G, 't') then
-            local is_ok, _t = pcall(require, 'luatest')
-            if is_ok then
-                rawset(_G, 't', _t)
-            else
-                require('log').warn('LUA_PATH is unset or incorrect, ' .. _t)
-            end
-        end
-    ]]
-    return self.net_box:eval(preamble .. code, ...)
+    return self.net_box:eval(code, ...)
 end
 
 --- Call remote function on the server by name.
@@ -535,8 +525,9 @@ end
 --    end, {1, 2})
 --    -- sum == 3
 --
+--    local t = require('luatest')
 --    server:exec(function()
---        -- luatest is always available as `t`
+--        -- luatest is available via `t` upvalue
 --        t.assert_equals(math.pi, 3)
 --    end)
 --    -- mytest.lua:12: expected: 3, actual: 3.1415926535898
@@ -547,24 +538,45 @@ function Server:exec(fn, args, options)
         error('net_box is not connected', 2)
     end
 
-    local ups = utils.upvalues(fn)
-    if next(ups) ~= nil then
+    local autorequired_pkgs = {'luatest'}
+    local passthrough_ups = {}
+    local other_ups = {}
+    for i = 1, debug.getinfo(fn, 'u').nups do
+        local name, value = debug.getupvalue(fn, i)
+        for _, pkg_name in ipairs(autorequired_pkgs) do
+            if value == package.loaded[pkg_name] then
+                passthrough_ups[name] = pkg_name
+                break
+            end
+        end
+        if not passthrough_ups[name] then
+            table.insert(other_ups, name)
+        end
+    end
+
+    if next(other_ups) ~= nil then
         local err = string.format(
             'bad argument #2 to exec (excess upvalues: %s)',
-            table.concat(ups, ', ')
+            table.concat(other_ups, ', ')
         )
         error(err, 2)
     end
 
-    return exec_tail(self:eval([[
-        local dump, args = ...
+    return exec_tail(self.net_box:eval([[
+        local dump, args, passthrough_ups = ...
         local fn = loadstring(dump)
+        for i = 1, debug.getinfo(fn, 'u').nups do
+            local name, _ = debug.getupvalue(fn, i)
+            if passthrough_ups[name] then
+                debug.setupvalue(fn, i, require(passthrough_ups[name]))
+            end
+        end
         if args == nil then
             return pcall(fn)
         else
             return pcall(fn, unpack(args))
         end
-    ]], {string.dump(fn), args}, options))
+    ]], {string.dump(fn), args, passthrough_ups}, options))
 end
 
 function Server:coverage(action)

test/autorequire_luatest_test.lua

@@ -1,4 +1,5 @@
 local fio = require('fio')
+local t = require('luatest')
 
 local g = t.group()
 local Server = t.Server
@@ -14,8 +15,7 @@ g.before_all(function()
         command = command,
         workdir = fio.pathjoin(datadir, 'common'),
         env = {
-            LUA_PATH =
-                root .. '/?.lua;' ..
+            LUA_PATH = root .. '/?.lua;' ..
                 root .. '/?/init.lua;' ..
                 root .. '/.rocks/share/tarantool/?.lua'
         },
@@ -37,29 +37,35 @@ g.after_all(function()
     fio.rmtree(datadir)
 end)
 
-g.test_exec_without_t = function()
+g.test_exec_without_upvalue = function()
     local actual = g.server:exec(function()
         return 1 + 1
     end)
     t.assert_equals(actual, 2)
 end
 
-g.test_exec_with_global_variable = function()
+g.test_exec_with_upvalue = function()
     g.server:exec(function()
         t.assert_equals(1, 1)
     end)
     t.assert_equals(1, 1)
+
+    local lt = require('luatest')
+    g.server:exec(function()
+        lt.assert_equals(1, 1)
+    end)
+    lt.assert_equals(1, 1)
 end
 
 g.test_exec_with_local_variable = function()
     g.server:exec(function()
-        local t = require('luatest')
+        local t = require('luatest')  -- luacheck: ignore 431
         t.assert_equals(1, 1)
     end)
     t.assert_equals(1, 1)
 end
 
-g.test_exec_with_local_duplicate = function()
+g.test_exec_with_upvalue_and_local_variable = function()
     g.server:exec(function()
         local tt = require('luatest')
         t.assert_equals(1, 1)
@@ -68,24 +74,11 @@ g.test_exec_with_local_duplicate = function()
     end)
 end
 
-g.test_eval_with_t = function()
-    local actual = g.server:eval([[
-        t.assert_equals(1, 1)
-        return 1
-    ]])
-    t.assert_equals(actual, 1)
-end
-
-g.before_test('test_exec_when_lua_path_is_unset', function()
+g.before_test('test_exec_when_luatest_not_found', function()
     -- Setup custom server without LUA_PATH variable
-    local workdir = fio.tempdir()
-    local log = fio.pathjoin(workdir, 'bad_env_server.log')
     g.bad_env_server = Server:new({
         command = command,
-        workdir = workdir,
-        env = {
-            TARANTOOL_LOG = log
-        },
+        workdir = fio.tempdir(),
         http_port = 8183,
         net_box_port = 3134,
     })
@@ -101,16 +94,13 @@ g.before_test('test_exec_when_lua_path_is_unset', function()
     g.bad_env_server:connect_net_box()
 end)
 
-g.test_exec_when_lua_path_is_unset = function()
-    g.bad_env_server:exec(function() return 1 + 1 end)
-
-    t.assert(
-        g.bad_env_server:grep_log(
-            "W> LUA_PATH is unset or incorrect, module 'luatest' not found"
-        )
+g.test_exec_when_luatest_not_found = function()
+    t.assert_error_msg_contains(
+        "module 'luatest' not found:", g.bad_env_server.exec, g.bad_env_server,
+        function() t.assert_equals(1, 1) end
     )
 end
 
-g.after_test('test_exec_when_lua_path_is_unset', function()
+g.after_test('test_exec_when_luatest_not_found', function()
     g.bad_env_server:drop()
 end)

test/server_instance.lua

@@ -5,15 +5,13 @@ local json = require('json')
 local workdir = os.getenv('TARANTOOL_WORKDIR')
 local listen = os.getenv('TARANTOOL_LISTEN')
 local http_port = os.getenv('TARANTOOL_HTTP_PORT')
-local log = os.getenv('TARANTOOL_LOG')
 
 local httpd = require('http.server').new('0.0.0.0', http_port)
 
-box.cfg({work_dir = workdir, log = log})
-box.schema.user.grant('guest', 'super', nil, nil, {if_not_exists=true})
+box.cfg({work_dir = workdir})
+box.schema.user.grant('guest', 'super', nil, nil, {if_not_exists = true})
 box.cfg({listen = listen})
 
-
 httpd:route({path = '/ping', method = 'GET'}, function()
     return {status = 200, body = 'pong'}
 end)