lua: Load bit and rex_pcre2 as though through require

Use luaL_requiref to load the bit and rex_pcre2 modules, which
adds them to the package.loaded table as though through require,
as Lua does with its included standard libraries.

This causes `require("bit")` and `require("rex_pcre2")` statements
in Lua dissectors to behave as expected, if albeit usually unecessary.
The tables are still added to the global environment as before.

Fix #20213

doc/release-notes.adoc

@@ -87,6 +87,11 @@ The following features are either new or have been significantly updated since v
 * DNP 3 (Distributed Network Protocol 3) is now supported in the Conversations
   and Endpoints table dialogs.
 
+* The Lua supplied preloaded libraries `bit` and `rex_pcre2` are loaded in
+  a way that adds them to the `package.loaded` table, as though through
+  `require`, so that `require("bit")` and `require("rex_pcre2")` statements
+  in Lua dissectors, while usually superfluous, behave as expected. wsbuglink:20213[]
+
 * The Windows installers now ship with Npcap 1.80.
   They previously shipped with Npcap 1.79.
 

doc/wsdg_src/wsdg_lua_support.adoc

@@ -448,7 +448,9 @@ in replacement for code written to use that library by simply replacing a
 `bit32 = require("bit32")` statement with `bit32 = bit`.
 
 [NOTE]
-The library is already loaded in the global environment as the `bit` table;
-Lua dissectors should not contain a `require("bit")` statement, which will give an
-error (unless another copy of the BitOp library is also accessible to the system Lua
-outside the Wireshark distributed code.)
+The library is already loaded in the global environment as the `bit` table; a
+statement like `local bit = require("bit")` is not necessary in Lua dissectors.
+On Wireshark versions prior to 4.6 this will give an error (unless another copy
+of the BitOp library is also accessible to the system Lua outside the Wireshark
+distributed code.) On Wireshark version 4.6 and later such statements behave as
+expected but are largely superfluous.

epan/wslua/lua_bitop.c

@@ -161,7 +161,6 @@ DIAG_ON(unreachable-code)
   }
 
   luaL_newlib(L, bit_funcs);
-  lua_setglobal(L, "bit"); /* added for wireshark */
-  return 0; /* changed from 1 to 0 for wireshark, since lua_setglobal now pops the table */
+  return 1;
 }
 

epan/wslua/make-reg.py

@@ -61,14 +61,15 @@ def generate_register_wslua_c(classes, functions, internal_functions):
     output_lines += ["\tlua_pushcfunction(L, func);"]
     output_lines += ["\tlua_call(L, 0, 0);"]
     output_lines += ["}\n"]
+    output_lines += ["static void wslua_reg_library(lua_State* L, const char *name, lua_CFunction func) {"]
+    output_lines += ['\tluaL_requiref(L, name, func, 1);']
+    output_lines += ['\tlua_pop(L, 1); /* remove lib */']
+    output_lines += ["}\n"]
     output_lines += ["void wslua_register_classes(lua_State* L) {"]
     for lua_class in classes:
         output_lines += ["\twslua_reg_module(L, \"{lua_class}\", {lua_class}_register);".format(lua_class=lua_class)]
-
-    output_lines += ["\twslua_reg_module(L, \"bit\", luaopen_bit);"]
-    output_lines += ["\tlua_pushcfunction(L, luaopen_rex_pcre2);"]
-    output_lines += ["\tlua_call(L, 0, 1);"]
-    output_lines += ["\tlua_setglobal(L, \"rex_pcre2\");"]
+    output_lines += ['\twslua_reg_library(L, "bit", luaopen_bit);']
+    output_lines += ['\twslua_reg_library(L, "rex_pcre2", luaopen_rex_pcre2);']
     output_lines += ["}\n"]
 
     output_lines += ["void wslua_register_functions(lua_State* L) {"]