extensions: the lua binding (and its example plug-in) is now marked as experimental.

We have too many issues with the lua binding, so until someone finds a
solution, mark it officially as experimental.

See discussion in: https://gitlab.gnome.org/GNOME/gimp/-/issues/11895#note_2225885

INSTALL.in

@@ -294,10 +294,18 @@ help in that regard:
      gdb or lldb for our new bug-reporting dialog
      "gegl:matting-levin" GEGL operation for alternative matting engine
      GJS for Javascript plug-ins
-     Lua 5.1 (or LuaJIT) and LGI for Lua plug-ins
      dot for "Show Image Graph" (unstable branches)
      xdg-desktop-portal implemented for your desktop for various D-Bus API (screenshot, color-picking…)
 
+ 24. Summary of experimental or unmaintained dependencies:
+
+     Lua 5.1 (or LuaJIT) and LGI: Lua plug-in example is disabled by
+       default because of stability issues with the Lua binding.
+
+     Webkit-GTK @WEBKITGTK_REQUIRED_VERSION@: the Help Browser and Webpage
+       plug-ins are disabled for lack of maintenance and issues with
+       Webkit-GTK
+
 
 
 Generic instructions for configuring and compiling auto-configured
@@ -397,8 +405,8 @@ These are:
   -Djavascript=false  If for some reason you don't want to install the
      JavaScript plug-ins, you can use -Djavascript=false.
 
-  -Dlua=false  If for some reason you don't want to install the
-     Lua plug-ins, you can use -Dlua=false.
+  -Dlua=true  Lua binding is experimental because of stability issues.
+     You may test the feature by enabling it.
 
   -Dvala-plugins=disabled  If for some reason you don't want to install the
      Vala plug-ins, you can use -Dvala-plugins=disabled.

extensions/meson.build

@@ -1,6 +1,6 @@
 subdir('goat-exercises')
 
-if not meson.is_cross_build() and is_variable('lua') and lua.found() and (platform_windows or not relocatable_bundle)
+if have_lua and not meson.is_cross_build() and is_variable('lua') and lua.found() and (platform_windows or not relocatable_bundle)
   lua_config = configuration_data()
   # For Windows, we set the binary name only.
   # For other OSes, we use the full path (when not in a relocatable

meson.build

@@ -1108,11 +1108,11 @@ endif
 
 ## Lua
 
-have_lua = false
+have_lua = get_option('lua')
 have_lua_output = have_lua
 # At time of writing, lua-lgi works with Lua 5.1, 5.2, 5.3 and LuaJIT2, but we
 # support only Lua 5.1 API. See: https://gitlab.gnome.org/GNOME/gimp/-/issues/11876
-if get_option('lua').allowed()
+if have_lua
   have_lua_lgi = false
 
   foreach lua_bin : [ 'luajit', 'lua5.1', 'lua-5.1', 'lua' ]
@@ -1165,14 +1165,13 @@ if get_option('lua').allowed()
     endif
   endforeach
 
-  have_lua = get_option('lua').enabled() or have_lua_lgi
-  if have_lua and not have_lua_lgi
+  if not have_lua_lgi
     lua_warning = '''
       Neither Luajit nor Lua 5.1, with lua-lgi support, was found.
       Or you are cross-compiling so we couldn't test lua-lgi support.
-      Lua plug-ins will be installed anyway but you should make sure that
-      luajit or lua and that LGI are available at installation, otherwise
-      installed plug-ins won't be usable.
+      Lua example plug-in (EXPERIMENTAL) will be installed anyway but you
+      should make sure that luajit or lua and that LGI are available at
+      installation, otherwise Lua plug-ins won't be usable.
       '''
     warning(lua_warning)
     warnings += lua_warning
@@ -2115,7 +2114,6 @@ final_message = [
 '''  PDF (export):        @0@'''.format(cairopdf.found()),
 '''  Print:               @0@'''.format(have_print),
 '''  Javascript plug-ins: @0@'''.format(have_javascript),
-'''  Lua plug-ins:        @0@'''.format(have_lua_output),
 '''  Vala plug-ins:       @0@'''.format(have_vala),
 '''  TWAIN (Win32):       @0@'''.format(platform_windows),
 '''  WMF:                 @0@'''.format(wmf.found()),
@@ -2126,6 +2124,9 @@ final_message = [
 '''  Email:               @0@'''.format(email_message),
 '''  FITS:                @0@'''.format(cfitsio_dep.found()),
 '',
+'''Experimental Plug-Ins (discouraged except for developers):''',
+'''  Lua plug-ins:        @0@'''.format(have_lua_output),
+'',
 '''Unmaintained Plug-Ins (discouraged except for developers):''',
 '''  Help Browser:        @0@'''.format(get_option('webkit-unmaintained')),
 '''  Webpage:             @0@'''.format(get_option('webkit-unmaintained')),

meson_options.txt

@@ -65,4 +65,4 @@ option('vector-icons',      type: 'boolean', value: true,   description: 'Use ve
 
 option('vala',              type: 'feature', value: 'auto', description: 'Build VAPI and Vala plugins')
 option('javascript',        type: 'feature', value: 'auto', description: 'Install Javascript plug-ins')
-option('lua',               type: 'feature', value: 'auto', description: 'Install Lua plug-ins')
+option('lua',               type: 'boolean', value: false,  description: 'Install Lua plug-ins (experimental)')