print: add callbacks at calling print() function

Those callbacks will be set from the console module (which integrates
readline into tarantool), so the print() output won't mix with readline
prompting.

Part of #7169

NO_DOC=no user visible changes, it is internal API
NO_TEST=will be tested in a next commit together with the console
        callbacks itself
NO_CHANGELOG=no user visible changes

src/CMakeLists.txt

@@ -64,6 +64,7 @@ lua_source(lua_sources lua/iconv.lua iconv_lua)
 lua_source(lua_sources lua/swim.lua swim_lua)
 lua_source(lua_sources lua/datetime.lua datetime_lua)
 lua_source(lua_sources lua/timezones.lua timezones_lua)
+lua_source(lua_sources lua/print.lua print_lua)
 
 # LuaJIT jit.* library
 lua_source(lua_sources ${LUAJIT_SOURCE_ROOT}/src/jit/bc.lua jit_bc_lua)

src/lua/init.c

@@ -154,7 +154,8 @@ extern char strict_lua[],
 	sysprof_collapse_lua[],
 	sysprof_lua[],
 	datetime_lua[],
-	timezones_lua[]
+	timezones_lua[],
+	print_lua[]
 #if defined(EMBED_LUAROCKS)
 	, luarocks_core_hardcoded_lua[],
 	luarocks_admin_cache_lua[],
@@ -308,6 +309,7 @@ static const char *lua_modules[] = {
 	"sysprof", sysprof_lua,
 	"timezones", timezones_lua,
 	"datetime", datetime_lua,
+	"internal.print", print_lua,
 	NULL
 };
 

src/lua/print.lua

@@ -0,0 +1,17 @@
+local M = {}
+
+M.raw_print = print
+
+-- before_cb() and after_cb() must not raise an error, must not
+-- yield. It would break expectations about the print() function.
+_G.print = function(...)
+    if M.before_cb ~= nil then
+        M.before_cb()
+    end
+    M.raw_print(...)
+    if M.after_cb ~= nil then
+        M.after_cb()
+    end
+end
+
+return M

test/luajit-test-init.lua

@@ -42,6 +42,53 @@ function _dofile(filename)
   return dofile(path_to_sources..filename)
 end
 
+-- Tarantool has its own print() function.
+--
+-- There are tests, which check something around a Lua/C function
+-- and use print() as a well known example of such function. The
+-- easiest way to mitigate problems in the tests is to replace
+-- print() back to the original one.
+--
+-- Our own print() is a simple wrapper around the original print()
+-- and performs some extra actions only in the interactive mode.
+-- It seems more or less safe to skip testing of the wrapper on
+-- LuaJIT's test suites.
+--
+-- Examples from LuaJIT test suites that fail with tarantool's
+-- print() function:
+--
+--  | PUC-Rio-Lua-5.1-tests/db.lua
+--  | ----------------------------
+--  | local a = debug.getinfo(print)
+--  | assert(a.what == "C" and a.short_src == "[C]")
+--  | -- In tarantool: a.what == "Lua"
+--  | -- In tarantool: a.short_src == "builtin/internal.print.lua"
+--
+--  | lua-Harness-tests/301-basic.t
+--  | -----------------------------
+--  | setfenv(print, {})
+--  | -- Expected error: 'setfenv' cannot change environment of
+--  | -- given object.
+--  | -- In tarantool: success.
+--
+--  | lua-Harness-tests/304-string.t
+--  | ------------------------------
+--  | string.dump(print)
+--  | -- Expected error: unable to dump given function.
+--  | -- In tarantool: success.
+--
+--  | lua-Harness-tests/304-string.t
+--  | ------------------------------
+--  | tostring(print)
+--  | Expected: 'function: builtin#29' (or similar).
+--  | In tarantool: 'function: 0x40e88018' (or similar).
+local print_M = package.loaded['internal.print']
+if print_M ~= nil then
+    rawset(_G, 'print', print_M.raw_print)
+    assert(print ~= nil)
+    assert(type(print) == 'function')
+end
+
 -- This is workaround introduced for flaky macosx tests reported by
 -- https://github.com/tarantool/tarantool/issues/7058
 collectgarbage('collect')