interpreter: add feature.allowed()

This method simplifies the conversion of Feature objects to booleans.
Often, one has to use the "not" operator in order to treat "auto"
and "enabled" the same way.

"allowed()" also works well in conjunction with the require method that
is introduced in the next patch.  For example,

  if get_option('foo').require(host_machine.system() == 'windows').allowed() then
    src += ['foo.c']
    config.set10('HAVE_FOO', 1)
  endif

can be used instead of

  if host_machine.system() != 'windows'
    if get_option('foo').enabled()
      error('...')
    endif
  endif
  if not get_option('foo').disabled() then
    src += ['foo.c']
    config.set10('HAVE_FOO', 1)
  endif

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/mesonbuild/interpreter/interpreterobjects.py b/mesonbuild/interpreter/interpreterobjects.py
index c70b8b5a1..5a37b48a7 100644
--- a/mesonbuild/interpreter/interpreterobjects.py
+++ b/mesonbuild/interpreter/interpreterobjects.py
@@ -72,6 +72,7 @@ class FeatureOptionHolder(InterpreterObject, ObjectHolder[coredata.UserFeatureOp
         self.name = name
         self.methods.update({'enabled': self.enabled_method,
                              'disabled': self.disabled_method,
+                             'allowed': self.allowed_method,
                              'auto': self.auto_method,
                              })
 
@@ -87,6 +88,11 @@ class FeatureOptionHolder(InterpreterObject, ObjectHolder[coredata.UserFeatureOp
 
     @noPosargs
     @permittedKwargs({})
+    def allowed_method(self, args, kwargs):
+        return not self.held_object.is_disabled()
+
+    @noPosargs
+    @permittedKwargs({})
     def auto_method(self, args, kwargs):
         return self.held_object.is_auto()