[libgweather/vapi-gate] build: Error out if enabled Vala bindings can't be built

[Emmanuele Bassi <ebassi src gnome org>]

commit 6120c5bb0951383284caf1031b9d56b4b40fbc86
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Fri Nov 19 12:51:06 2021 +0000

    build: Error out if enabled Vala bindings can't be built
    
    If the Vala bindings were explicitly enabled but cannot be built because
    of a missing dependency, we should error out immediately.

 libgweather/meson.build | 8 ++++++++
 1 file changed, 8 insertions(+)
---
diff --git a/libgweather/meson.build b/libgweather/meson.build
index b9371b8e..c061bd79 100644
--- a/libgweather/meson.build
+++ b/libgweather/meson.build
@@ -204,6 +204,14 @@ enable_vala = get_option('enable_vala')
 vapigen = find_program('vapigen', required: enable_vala == 'true')
 if enable_vala == 'auto' or enable_vala == 'true'
   build_vapi = vapigen.found() and get_option('introspection')
+  if enable_vala == 'true' and not build_vapi
+    if not vapigen.found()
+      msg = 'vapigen not found'
+    elif not get_option('introspection')
+      msg = 'introspection disabled'
+    endif
+    error('Vala bindings were enabled but cannot be generated: @0@'.format(msg))
+  endif
 else
   build_vapi = false
 endif