compose: Allow building without SVG support

Apparently, bootstrapping a system with Rust in the toolchain is still a
major pain, and since rsvg is being rewritten in Rust, AppStream is
dragging it in if compose is enabled.
Of course, building AppStream without SVG support is not a great idea,
unless the only thing you are using appstream-compose for is non-GUI
applications.
As this is apparently the case for some Flatpak runtimes, we allow
disabling rsvg, but also complain very loudly as soon as we encounter an
SVG icon. This change should simplify early bootstrap and allow building
the complete appstream-compose at a later time in the build process.

Resolves: ximion#434

compose/asc-canvas.c

@@ -30,7 +30,9 @@
 
 #include <cairo.h>
 #include <cairo-ft.h>
+#ifdef HAVE_SVG_SUPPORT
 #include <librsvg/rsvg.h>
+#endif
 
 #include "asc-font-private.h"
 #include "asc-image.h"
@@ -152,6 +154,7 @@ asc_canvas_get_height (AscCanvas *canvas)
 gboolean
 asc_canvas_render_svg (AscCanvas *canvas, GInputStream *stream, GError **error)
 {
+#ifdef HAVE_SVG_SUPPORT
 	AscCanvasPrivate *priv = GET_PRIVATE (canvas);
 	RsvgHandle *handle = NULL;
 	gboolean ret = FALSE;
@@ -220,6 +223,15 @@ asc_canvas_render_svg (AscCanvas *canvas, GInputStream *stream, GError **error)
 	if (handle != NULL)
 		g_object_unref (handle);
 	return ret;
+#else
+	g_warning ("Unable to render SVG graphic: AppStream built without SVG support.");
+	g_set_error_literal (error,
+			     ASC_CANVAS_ERROR,
+			     ASC_CANVAS_ERROR_UNSUPPORTED,
+			     "AppStream was built without SVG support. This is an issue with your AppStream distribution. "
+			     "Please rebuild AppStream with SVG support enabled or contact your distributor to enable it for you.");
+	return FALSE;
+#endif
 }
 
 /**

compose/asc-canvas.h

@@ -35,16 +35,18 @@ G_DECLARE_FINAL_TYPE (AscCanvas, asc_canvas, ASC, CANVAS, GObject)
 
 /**
  * AscCanvasError:
- * @ASC_CANVAS_ERROR_FAILED:	Generic failure.
- * @ASC_CANVAS_ERROR_DRAWING:	Drawing operation failed.
- * @ASC_CANVAS_ERROR_FONT:	Issue with font or font selection.
+ * @ASC_CANVAS_ERROR_FAILED:	  Generic failure.
+ * @ASC_CANVAS_ERROR_DRAWING:	  Drawing operation failed.
+ * @ASC_CANVAS_ERROR_FONT:	  Issue with font or font selection.
+ * @ASC_CANVAS_ERROR_UNSUPPORTED: The requested action was not supported.
  *
  * A drawing error.
  **/
 typedef enum {
 	ASC_CANVAS_ERROR_FAILED,
 	ASC_CANVAS_ERROR_DRAWING,
 	ASC_CANVAS_ERROR_FONT,
+	ASC_CANVAS_ERROR_UNSUPPORTED,
 	/*< private >*/
 	ASC_CANVAS_ERROR_LAST
 } AscCanvasError;

compose/meson.build

@@ -60,12 +60,18 @@ asclib_res = glib.compile_resources (
 )
 
 # extra dependencies we need just for AppStream Compose
-cairo_dep      = dependency('cairo', version : '>= 1.12')
+cairo_dep      = dependency('cairo', version: '>= 1.12')
 gdkpixbuf_dep  = dependency('gdk-pixbuf-2.0')
-rsvg_dep       = dependency('librsvg-2.0', version : '>= 2.48')
 freetype_dep   = dependency('freetype2')
 pango_dep      = dependency('pango')
 fontconfig_dep = dependency('fontconfig')
+m_dep          = cc.find_library('m', required: false)
+if get_option ('svg-support')
+    rsvg_dep       = dependency('librsvg-2.0', version: '>= 2.48')
+else
+    rsvg_dep = dependency('', required: false)
+    warning('Building without SVG support. Therefore appstream-compose will be unable to render SVG icons.')
+endif
 
 appstream_compose_lib = library ('appstream-compose',
     [ascompose_src,
@@ -76,6 +82,7 @@ appstream_compose_lib = library ('appstream-compose',
     soversion: '0',
     version: as_version,
     dependencies: [appstream_dep,
+                   m_dep,
                    gio_dep,
                    cairo_dep,
                    gdkpixbuf_dep,
@@ -101,7 +108,7 @@ pkgc.generate(
                'gio-2.0',
                'gobject-2.0',
                'gdk-pixbuf-2.0',
-               'appstream']
+               'appstream'],
 )
 
 appstream_compose_dep = declare_dependency(

meson.build

@@ -49,6 +49,7 @@ conf.set_quoted('SYSCONFDIR',
                            get_option('sysconfdir')))
 conf.set('HAVE_APT_SUPPORT', get_option('apt-support'))
 conf.set('HAVE_STEMMING', get_option('stemming'))
+conf.set('HAVE_SVG_SUPPORT', get_option('svg-support'))
 
 configure_file(output: 'config.h', configuration: conf)
 root_inc_dir = include_directories ('.')

meson_options.txt

@@ -28,6 +28,11 @@ option('gir',
        value : true,
        description : 'Build introspection data'
 )
+option('svg-support',
+       type : 'boolean',
+       value : true,
+       description : 'SVG graphics support for compose (only disable this for bootstrapping purposes)'
+)
 
 option('docs',
        type : 'boolean',