Allow exporting Lua symbols

Which optionally enables loading Lua shared modules from within even static TPT. Not that anyone actually needs this.

This currently can't work on Windows because DLLs there import symbols by [module name, symbol name] rather than just symbol name. One could in theory export Lua symbols from TPT (I don't know the exact MSVC hack this would require, .def files?) and place a lua51.dll next to the executable that just re-exports them, see https://learn.microsoft.com/en-us/cpp/build/reference/exports?view=msvc-170 , but I've yet to try this.

meson.build

@@ -376,6 +376,22 @@ if host_platform == 'emscripten'
 		'-o', app_exe + '.js', # so we get a .wasm, and a .js
 	]
 endif
+if get_option('export_lua_symbols')
+	if is_static and lua_variant != 'none' and not project_export_dynamic
+		if host_platform == 'windows'
+			error('Lua symbols are currently impossible to export correctly on Windows')
+		elif c_compiler.has_link_argument('-Wl,--export-dynamic-symbol')
+			project_link_args += [
+				'-Wl,--export-dynamic-symbol=lua_*',
+				'-Wl,--export-dynamic-symbol=luaL_*',
+				'-Wl,--export-dynamic-symbol=luaopen_*',
+			]
+		else
+			warning('your linker does not support -Wl,--export-dynamic-symbol so Meson will be instructed to export all symbols in order to enable loading Lua shared modules, which may blow up the size of the resulting binary')
+			project_export_dynamic = true
+		endif
+	endif
+endif
 
 if get_option('build_powder')
 	powder_deps += project_deps + [

meson_options.txt

@@ -305,3 +305,9 @@ option(
 	value: true,
 	description: 'Ask Windows nicely for UTF-8 as the codepage'
 )
+option(
+	'export_lua_symbols',
+	type: 'boolean',
+	value: false,
+	description: 'Export Lua symbols to enable loading of Lua shared modules'
+)