modules: Fix build on Visual Studio

Visual Studio does not allow decorating functions with '__declspec (dllexport)'
if a prototype exists and is not decorated with '__declspec (dllexport)' as
well, so we cannot just decorate g_io_module_[load|unload|query] in the various
module sources with G_MODULE_EXPORT because the prototypes of these functions
have been marked with _GLIB_EXTERN, which equates to 'extern' unless overridden

Fix this by overriding _GLIB_EXTERN with the appropriate visibility flag, as we
have used to define _GDK_EXTERN.  Unfortunately, we can't just use _GDK_EXTERN
G_MODULE_EXPORT as they may have not been defined yet for our use

Do this across the board for all modules, even if they are not buildable on
Visual Studio nor Windows, for consistency's sake.

meson.build

@@ -286,15 +286,19 @@ endif
 common_cflags = cc.get_supported_arguments(test_cflags)
 
 # Symbol visibility
+
+if os_win32
+  visibility_define = '__declspec(dllexport) extern'
+else
+  visibility_define = '__attribute__((visibility("default"))) extern'
+endif
+
 if get_option('default_library') != 'static'
+  cdata.set('_GDK_EXTERN', visibility_define)
   if os_win32
     cdata.set('DLL_EXPORT', true)
-    cdata.set('_GDK_EXTERN', '__declspec(dllexport) extern')
-    if cc.get_id() != 'msvc'
-      common_cflags += ['-fvisibility=hidden']
-    endif
-  else
-    cdata.set('_GDK_EXTERN', '__attribute__((visibility("default"))) extern')
+  endif
+  if cc.get_id() != 'msvc'
     common_cflags += ['-fvisibility=hidden']
   endif
 endif

modules/media/gtkgstmediafile.c

@@ -97,7 +97,6 @@ G_DEFINE_TYPE_EXTENDED (GtkGstMediaFile, gtk_gst_media_file, GTK_TYPE_MEDIA_FILE
                         G_IMPLEMENT_INTERFACE (GDK_TYPE_PAINTABLE,
                                                gtk_gst_media_file_paintable_init))
 
-G_MODULE_EXPORT
 void
 g_io_module_load (GIOModule *module)
 {
@@ -109,7 +108,6 @@ g_io_module_load (GIOModule *module)
                                   10);
 }
 
-G_MODULE_EXPORT
 G_GNUC_NORETURN
 void
 g_io_module_unload (GIOModule *module)
@@ -117,7 +115,6 @@ g_io_module_unload (GIOModule *module)
   g_assert_not_reached ();
 }
 
-G_MODULE_EXPORT
 char **
 g_io_module_query (void)
 {

modules/media/meson.build

@@ -23,7 +23,11 @@ endif
 media_subdir = 'gtk-4.0/@0@/media'.format(gtk_binary_version)
 media_install_dir = join_paths(get_option('libdir'), media_subdir)
 
-extra_c_args = ['-DGTK_COMPILATION']
+extra_c_args = [
+  '-DGTK_COMPILATION',
+  '-D_GLIB_EXTERN=@0@'.format(visibility_define),
+]
+
 extra_c_args += common_cflags
 
 if media_backends.contains('ffmpeg')

modules/printbackends/gtkprintbackendcloudprint.c

@@ -103,7 +103,6 @@ void                 t_goa_account_free                 (gpointer data);
 
 G_DEFINE_DYNAMIC_TYPE (GtkPrintBackendCloudprint, gtk_print_backend_cloudprint, GTK_TYPE_PRINT_BACKEND)
 
-G_MODULE_EXPORT
 void
 g_io_module_load (GIOModule *module)
 {
@@ -119,13 +118,11 @@ g_io_module_load (GIOModule *module)
                                   10);
 }
 
-G_MODULE_EXPORT
 void
 g_io_module_unload (GIOModule *module)
 {
 }
 
-G_MODULE_EXPORT
 char **
 g_io_module_query (void)
 {

modules/printbackends/gtkprintbackendcups.c

@@ -236,7 +236,6 @@ static void                 secrets_service_vanished_cb             (GDBusConnec
 
 G_DEFINE_DYNAMIC_TYPE(GtkPrintBackendCups, gtk_print_backend_cups, GTK_TYPE_PRINT_BACKEND)
 
-G_MODULE_EXPORT
 void
 g_io_module_load (GIOModule *module)
 {
@@ -251,13 +250,11 @@ g_io_module_load (GIOModule *module)
                                   10);
 }
 
-G_MODULE_EXPORT
 void
 g_io_module_unload (GIOModule *module)
 {
 }
 
-G_MODULE_EXPORT
 char **
 g_io_module_query (void)
 {

modules/printbackends/gtkprintbackendfile.c

@@ -102,7 +102,6 @@ static GtkPageSetup *       file_printer_get_default_page_size     (GtkPrinter
 
 G_DEFINE_DYNAMIC_TYPE(GtkPrintBackendFile, gtk_print_backend_file, GTK_TYPE_PRINT_BACKEND)
 
-G_MODULE_EXPORT
 void
 g_io_module_load (GIOModule *module)
 {
@@ -116,13 +115,11 @@ g_io_module_load (GIOModule *module)
                                   10);
 }
 
-G_MODULE_EXPORT
 void
 g_io_module_unload (GIOModule *module)
 {
 }
 
-G_MODULE_EXPORT
 char **
 g_io_module_query (void)
 {

modules/printbackends/gtkprintbackendlpr.c

@@ -83,7 +83,6 @@ static void                 gtk_print_backend_lpr_print_stream    (GtkPrintBacke
 
 G_DEFINE_DYNAMIC_TYPE (GtkPrintBackendLpr, gtk_print_backend_lpr, GTK_TYPE_PRINT_BACKEND)
 
-G_MODULE_EXPORT
 void
 g_io_module_load (GIOModule *module)
 {
@@ -97,13 +96,11 @@ g_io_module_load (GIOModule *module)
                                   10);
 }
 
-G_MODULE_EXPORT
 void
 g_io_module_unload (GIOModule *module)
 {
 }
 
-G_MODULE_EXPORT
 char **
 g_io_module_query (void)
 {

modules/printbackends/meson.build

@@ -68,6 +68,7 @@ printbackends_args = [
   '-DGTK_COMPILATION',
   '-DGTK_DISABLE_DEPRECATION_WARNINGS',
   '-DGTK_PRINT_BACKEND_ENABLE_UNSUPPORTED',
+  '-D_GLIB_EXTERN=@0@'.format(visibility_define),
 ] + common_cflags
 
 if print_backends.contains('cups')