Add tristate user option required/not-required/disabled

docs/markdown/Build-options.md

@@ -19,6 +19,7 @@ option('combo_opt', type : 'combo', choices : ['one', 'two', 'three'], value : '
 option('integer_opt', type : 'integer', min : 0, max : 5, value : 3) # Since 0.45.0
 option('free_array_opt', type : 'array', value : ['one', 'two'])
 option('array_opt', type : 'array', choices : ['one', 'two', 'three'], value : ['one', 'two'])
+option('some_feature', type : 'dependency', value : 'required')
 ```
 
 All types allow a `description` value to be set describing the option,
@@ -60,6 +61,23 @@ default.
 
 This type is available since version 0.44.0
 
+### Dependency
+
+A `dependency` options has tree states: `required`, `not-required` or
+`disabled`. It is special cased by [`get_option()`](Reference-manual.md#get_option)
+and instead of returning their string representation it returns `true`, `false`
+or [`Disabler`](Reference-manual.md#disabler) respectively.
+
+It is indented to be passed directly to the `required` keyword of
+[`dependency()`](Reference-manual.md#dependency) function, which will cause it
+to return a `Disabler` if the option is set to `disabled`.
+
+```meson
+d = dependency('foo', required : get_option('foo_option'))
+app = executable('myapp', 'main.c', dependencies : [d])
+```
+
+This type is available since version 0.46.0
 
 ## Using build options
 

mesonbuild/coredata.py

@@ -158,6 +158,10 @@ def validate_value(self, value, user_input=True):
                     ', '.join(bad), ', '.join(self.choices)))
         return newvalue
 
+class UserDependencyOption(UserComboOption):
+    def __init__(self, name, description, value, yielding=None):
+        super().__init__(name, description, ['required', 'not-required', 'disabled'], value, yielding)
+
 
 # This class contains all data that must persist over multiple
 # invocations of Meson. It is roughly the same thing as

mesonbuild/interpreter.py

@@ -1911,6 +1911,13 @@ def func_get_option(self, nodes, args, kwargs):
             if opt.yielding and ':' in optname:
                 # If option not present in superproject, keep the original.
                 opt = self.environment.coredata.user_options.get(undecorated_optname, opt)
+            if isinstance(opt, coredata.UserDependencyOption):
+                if opt.value == 'required':
+                    return True
+                elif opt.value == 'not-required':
+                    return False
+                else:
+                    return Disabler()
             return opt.value
         except KeyError:
             pass

mesonbuild/optinterpreter.py

@@ -127,11 +127,19 @@ def string_array_parser(name, description, kwargs):
                                     choices=choices,
                                     yielding=kwargs.get('yield', coredata.default_yielding))
 
+@permitted_kwargs({'value', 'yield'})
+def DependencyParser(name, description, kwargs):
+    return coredata.UserDependencyOption(name,
+                                         description,
+                                         kwargs.get('value', 'required'),
+                                         yielding=kwargs.get('yield', coredata.default_yielding))
+
 option_types = {'string': StringParser,
                 'boolean': BooleanParser,
                 'combo': ComboParser,
                 'integer': IntegerParser,
                 'array': string_array_parser,
+                'dependency': DependencyParser,
                 }
 
 class OptionInterpreter: