meson/docs/markdown/snippets/notfound_message.md

New not_found_message for dependency

You can now specify a not_found_message that will be printed if the specified dependency was not found. The point is to convert constructs that look like this:

d = dependency('something', required: false)
if not d.found()
  message('Will not be able to do something.')
endif

Into this:

d = dependency('something',
  required: false,
  not_found_message: 'Will not be able to do something.')

Or constructs like this:

d = dependency('something', required: false)
if not d.found()
  error('Install something by doing XYZ.')
endif

into this:

d = dependency('something',
  not_found_message: 'Install something by doing XYZ.')

Which works, because the default value of required is true.