Allow building without tests and demos

This is meant to cut down build time in flatpak and similar
situations. Since it produces technically incomplete builds,
we list these options in the status output at the end of
the meson run.

docs/reference/gtk/building.sgml

@@ -462,12 +462,12 @@ How to compile GTK+ itself
       </formalpara>
 
       <formalpara>
-        <title><systemitem>-Denable-x11-backend</systemitem>,
-          <systemitem>-Denable-win32-backend</systemitem>,
-          <systemitem>-Denable-quartz-backend</systemitem>,
-          <systemitem>-Denable-broadway-backend</systemitem>,
-          <systemitem>-Denable-wayland-backend</systemitem>, and
-          <systemitem>-Denable-mir-backend</systemitem></title>
+        <title><systemitem>enable-x11-backend</systemitem>,
+          <systemitem>enable-win32-backend</systemitem>,
+          <systemitem>enable-quartz-backend</systemitem>,
+          <systemitem>enable-broadway-backend</systemitem>,
+          <systemitem>enable-wayland-backend</systemitem>, and
+          <systemitem>enable-mir-backend</systemitem></title>
 
         <para>
           Enable specific backends for GDK.  If none of these options
@@ -480,6 +480,18 @@ How to compile GTK+ itself
         </para>
       </formalpara>
 
+      <formalpara>
+        <title><systemitem>build-tests</systemitem>
+          <systemitem>demos</systemitem></title>
+
+        <para>
+          By default, GTK+ will build quite a few tests and demos.
+          While these are useful on a developer system, they are not
+          needed when GTK+ is built e.g. for a flatpak runtime. These
+          options allow to disable building tests and demos.
+        </para>
+      </formalpara>
+
     </refsect1>
 
 </refentry>

meson.build

@@ -520,11 +520,15 @@ subdir('modules/input')
 subdir('gdk')
 subdir('gsk')
 subdir('gtk')
-subdir('demos')
 subdir('modules')
-subdir('tests')
-subdir('testsuite')
-subdir('examples')
+if get_option('enable-tests')
+  subdir('tests')
+  subdir('testsuite')
+endif
+if get_option('demos')
+  subdir('demos')
+  subdir('examples')
+endif
 
 # config.h
 configure_file(input: 'config.h.meson',
@@ -615,8 +619,10 @@ summary = [
   'GTK+ @0@ (@1@)'.format(gtk_version, gtk_api_version),
   '',
   '  Enabled backends: @0@'.format(pkg_targets.strip()),
-  '  Documentation: @0@'.format(get_option('enable-documentation')),
   '  Vulkan support: @0@'.format(have_vulkan),
+  '  Tests: @0@'.format(get_option('build-tests')),
+  '  Documentation: @0@'.format(get_option('enable-documentation')),
+  '  Demos: @0@'.format(get_option('demos')),
   '------',
   ''
 ]

meson_options.txt

@@ -36,3 +36,7 @@ option('enable-man-pages', type: 'boolean', value: 'false',
   description : 'Build man pages for installed tools')
 option('enable-gir', type: 'boolean', value: 'true',
   description : 'Build introspection data (requires gobject-introspection)')
+option('demos', type: 'boolean', value: 'true',
+  description : 'Build demos and example programs')
+option('build-tests', type: 'boolean', value: 'true',
+  description : 'Build tests')