[ghex/support-block-devices-part-trois: 3/5] buf/doc/appwin: Load default backend plugins without using ifdefs

[Logan Rathbone <larathbone src gnome org>]

commit 7d33b800477b5b01ebe07750634752dfe39f4053
Author: Logan Rathbone <poprocks gmail com>
Date:   Wed Jun 8 00:10:02 2022 -0400

    buf/doc/appwin: Load default backend plugins without using ifdefs
    
    appwin: Tweak nag screen accordingly. Change messaging a bit.
    doc: change hierarchical selection of buffer backend.
    buf: document slight change in hex_buffer_util_new behaviour when a
    non-existent plugin is requested (return NULL instead of falling back to
    malloc).

 meson.build                   |  7 -------
 src/ghex-application-window.c | 37 ++++++++++++++++---------------------
 src/ghex-application-window.h |  1 +
 src/hex-buffer-iface.c        | 31 +++++++++++++++++++++----------
 src/hex-document.c            | 18 +++++++++++-------
 5 files changed, 49 insertions(+), 45 deletions(-)
---
diff --git a/meson.build b/meson.build
index 8fc22ea..63d6c15 100644
--- a/meson.build
+++ b/meson.build
@@ -90,13 +90,6 @@ config_h.set('LOCALEDIR', 'PACKAGE_LOCALE_DIR')
 
 config_h.set('CONFIG_H_SHADED_BOX_MAX', shaded_box_max)
 
-# nb: this config.h flag will likely be removed in a future release
-#if mmap_backend
-#  config_h.set('BACKEND_MMAP', true)
-if direct_backend
-  config_h.set('BACKEND_DIRECT', true)
-endif
-
 config_h.set_quoted('LIBGTKHEX_RELEASE_STRING', 'gtkhex-@0@.0'.format(libgtkhex_api_version))
 
 config_h.set('STATIC_HTML_HELP', get_option('static-html-help'))
diff --git a/src/ghex-application-window.c b/src/ghex-application-window.c
index 2c26296..0979f49 100644
--- a/src/ghex-application-window.c
+++ b/src/ghex-application-window.c
@@ -37,9 +37,7 @@
 #define ACTIVE_GH      \
        (ghex_application_window_get_hex (self))
 
-#ifndef BACKEND_MMAP
 static GFile *tmp_global_gfile_for_nag_screen;
-#endif
 
 /* This is dumb, but right now I can't think of a simpler solution. */
 static gpointer extra_user_data;
@@ -2036,7 +2034,6 @@ ghex_application_window_add_hex (GHexApplicationWindow *self,
        show_hex_notebook (self);
 }
 
-#ifndef BACKEND_MMAP
 /* Helper */
 static void
 nag_screen_response_cb (GtkDialog *nag_screen,
@@ -2065,11 +2062,12 @@ do_nag_screen (GHexApplicationWindow *self)
                GtkWidget *nag_screen;
                char *msg = _("You are attempting to open a file 1GB or larger.\n\n"
                                "This can make GHex and your machine unstable as the file "
-                               "will be loaded into memory.\n\n"
+                               "will be loaded into memory, using the active backend.\n\n"
                                "Are you sure you want to proceed?\n\n"
                                "This message will not be shown again for the remainder of "
                                "this GHex session.\n\n"
-                               "This limitation will be removed in a future version of GHex.");
+                               "To avoid this message from appearing, try using a different "
+                               "buffer backend.");
        
                g_printerr ("%s", msg);
                g_printerr ("\n");
@@ -2084,7 +2082,6 @@ do_nag_screen (GHexApplicationWindow *self)
                                G_CALLBACK(nag_screen_response_cb), self);
                gtk_widget_show (nag_screen);
 }
-#endif
 
 /* also takes extra_user_data ! Hooray for cheap shortcuts! */
 static void
@@ -2132,25 +2129,10 @@ ghex_application_window_open_file (GHexApplicationWindow *self, GFile *file)
 {
        HexDocument *doc;
        HexWidget *gh = NULL;
-#ifndef BACKEND_MMAP
        static gboolean nag_screen_shown = FALSE;
-#endif
 
        g_return_if_fail (GHEX_IS_APPLICATION_WINDOW(self));
 
-#ifndef BACKEND_MMAP
-       if (! nag_screen_shown)
-               /* FIXME: Temporary nag-screen until we get the underlying issues
-                * sorted. */
-               if (hex_buffer_util_get_file_size (file) >= 1073741824)
-               {
-                       nag_screen_shown = TRUE;
-                       tmp_global_gfile_for_nag_screen = file;
-                       do_nag_screen (self);
-                       return;
-               }
-#endif
-
        /* If we get it from the GApp :open signal, it's tfr:none - once
         * HexDocument gets hold of it, though, it _refs it itself so we don't need
         * to hold onto it.
@@ -2159,6 +2141,19 @@ ghex_application_window_open_file (GHexApplicationWindow *self, GFile *file)
        doc = hex_document_new_from_file (file);
        g_object_unref (file);
 
+       if (HEX_IS_BUFFER_MALLOC (hex_document_get_buffer (doc)) &&
+                       ! nag_screen_shown)
+       {
+               if (hex_buffer_util_get_file_size (file) >= 1073741824)
+               {
+                       nag_screen_shown = TRUE;
+                       tmp_global_gfile_for_nag_screen = file;
+                       do_nag_screen (self);
+                       g_object_unref (doc);
+                       return;
+               }
+       }
+
        if (doc)
                gh = HEX_WIDGET(hex_widget_new (doc));
 
diff --git a/src/ghex-application-window.h b/src/ghex-application-window.h
index 199a16a..ff27ee2 100644
--- a/src/ghex-application-window.h
+++ b/src/ghex-application-window.h
@@ -38,6 +38,7 @@
 #include "converter.h"
 #include "preferences.h"
 #include "common-ui.h"
+#include "hex-buffer-malloc.h"
 
 G_BEGIN_DECLS
 
diff --git a/src/hex-buffer-iface.c b/src/hex-buffer-iface.c
index 9093f7b..6133765 100644
--- a/src/hex-buffer-iface.c
+++ b/src/hex-buffer-iface.c
@@ -351,10 +351,13 @@ hex_buffer_get_payload_size (HexBuffer *self)
  *
  * Returns: (transfer full): a pointer to a valid implementation of a
  * [iface@Hex.Buffer] interface, pre-cast as type #HexBuffer, or %NULL if
- * the operation failed.
+ * the operation failed. Starting with 4.2, if a specific backend is requested,
+ * and the system supports plugins as a whole but cannot load that specified
+ * plugin, %NULL will be returned as though the operation failed, so as to
+ * customize the fallback scheme programmatically.
  */
-
-HexBuffer * hex_buffer_util_new (const char *plugin, GFile *file)
+HexBuffer *
+hex_buffer_util_new (const char *plugin, GFile *file)
 {
        GModule *module;
        HexBufferNewFunc func = NULL;
@@ -366,9 +369,15 @@ HexBuffer * hex_buffer_util_new (const char *plugin, GFile *file)
         * if NULL is passed, fall right back to `malloc` since it's the only one
         * baked in.
         */
-       if (!g_module_supported () || !plugin)
+       if (! plugin)
+       {
+               g_debug ("No plugin specified; falling back to the `malloc` backend.");
+               return hex_buffer_malloc_new (file);
+       }
+       if (! g_module_supported () || !plugin)
        {
-               g_debug ("Modules not supported or NULL passed - falling back to `malloc` backend.");
+               g_message ("Modules not supported on this system; "
+                               "falling back to `malloc` backend.");
                return hex_buffer_malloc_new (file);
        }
 
@@ -379,14 +388,13 @@ HexBuffer * hex_buffer_util_new (const char *plugin, GFile *file)
 
        if (! module)
        {
-               g_warning ("Unable to load plugin at %s - falling back to `malloc` backend",
-                               plugin_path);
-               func = hex_buffer_malloc_new;
+               g_debug ("Unable to locate/load plugin at %s", plugin_path);
+               func = NULL;
        }
        else if (! g_module_symbol (module, symbol_name, (gpointer *)&func) ||
                        func == NULL)
        {
-               g_warning ("Plugin found at %s - but unable to locate symbol: %s - "
+               g_message ("Plugin found at %s - but unable to locate symbol: %s - "
                                "falling back to `malloc` backend.",
                                plugin_path, symbol_name);
                func = hex_buffer_malloc_new;
@@ -402,7 +410,10 @@ HexBuffer * hex_buffer_util_new (const char *plugin, GFile *file)
        g_free (plugin_path);
        g_free (symbol_name);
 
-       return func (file);
+       if (func)
+               return func (file);
+       else
+               return NULL;
 }
 
 /**
diff --git a/src/hex-document.c b/src/hex-document.c
index 2d3afa1..7376a6c 100644
--- a/src/hex-document.c
+++ b/src/hex-document.c
@@ -356,13 +356,17 @@ hex_document_class_init (HexDocumentClass *klass)
 static void
 hex_document_init (HexDocument *doc)
 {
-#ifdef BACKEND_MMAP
-       doc->buffer = hex_buffer_util_new ("mmap", NULL);
-#elif defined BACKEND_DIRECT
-       doc->buffer = hex_buffer_util_new ("direct", NULL);
-#else
-       doc->buffer = hex_buffer_util_new (NULL, NULL);
-#endif
+       HexBuffer *try_buf = NULL;
+
+       /* FIXME - make this a setting; preferred default backend, or
+        * what-have-you.
+        */
+       try_buf = hex_buffer_util_new ("mmap", NULL);
+       if (! try_buf)
+               try_buf = hex_buffer_util_new (NULL, NULL);
+
+       g_assert (try_buf != NULL);
+       doc->buffer = try_buf;
 
        doc->undo_max = DEFAULT_UNDO_DEPTH;
 }