User options can "yield to" a user option of the same name in superproject. Closes ##2853.

docs/markdown/Build-options.md

@@ -108,3 +108,21 @@ double quotes.
 **NOTE:** If you cannot call `meson configure` you likely have a old
   version of Meson. In that case you can call `mesonconf` instead, but
   that is deprecated in newer versions
+
+## Yielding to superproject option
+
+Suppose you have a master project and a subproject. In some cases it
+might be useful to have an option that has the same value in both of
+them. This can be achieved with the `yield` keyword. Suppose you have
+an option definition like this:
+
+```meson
+option('some_option', type : 'string', value : 'value', yield : true)
+```
+
+If you build this project on its own, this option behaves like
+usual. However if you build this project as a subproject of another
+project which also has an option called `some_option`, then calling
+`get_option` returns the value of the superproject. If the value of
+`yield` is `false`, `get_option` returns the value of the subproject's
+option.

docs/markdown/snippets/yield.md

@@ -0,0 +1,8 @@
+## Yielding subproject option to superproject
+
+Normally project options are specific to the current project. However
+sometimes you want to have an option whose value is the same over all
+projects. This can be achieved with the new `yield` keyword for
+options. When set to `true`, getting the value of this option in
+`meson.build` files gets the value from the option with the same name
+in the master project (if such an option exists).

mesonbuild/coredata.py

@@ -1,5 +1,4 @@
-
-# Copyright 2012-2017 The Meson development team
+# Copyright 2012-2018 The Meson development team
 
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -25,12 +24,19 @@ import ast
 version = '0.45.0.dev1'
 backendlist = ['ninja', 'vs', 'vs2010', 'vs2015', 'vs2017', 'xcode']
 
+default_yielding = False
+
 class UserOption:
-    def __init__(self, name, description, choices):
+    def __init__(self, name, description, choices, yielding):
         super().__init__()
         self.name = name
         self.choices = choices
         self.description = description
+        if yielding is None:
+            yielding = default_yielding
+        if not isinstance(yielding, bool):
+            raise MesonException('Value of "yielding" must be a boolean.')
+        self.yielding = yielding
 
     # Check that the input is a valid value and return the
     # "cleaned" or "native" version. For example the Boolean
@@ -39,8 +45,8 @@ class UserOption:
         raise RuntimeError('Derived option class did not override validate_value.')
 
 class UserStringOption(UserOption):
-    def __init__(self, name, description, value, choices=None):
-        super().__init__(name, description, choices)
+    def __init__(self, name, description, value, choices=None, yielding=None):
+        super().__init__(name, description, choices, yielding)
         self.set_value(value)
 
     def validate(self, value):
@@ -56,8 +62,8 @@ class UserStringOption(UserOption):
         return value
 
 class UserBooleanOption(UserOption):
-    def __init__(self, name, description, value):
-        super().__init__(name, description, [True, False])
+    def __init__(self, name, description, value, yielding=None):
+        super().__init__(name, description, [True, False], yielding)
         self.set_value(value)
 
     def tobool(self, thing):
@@ -79,8 +85,8 @@ class UserBooleanOption(UserOption):
         return self.tobool(value)
 
 class UserIntegerOption(UserOption):
-    def __init__(self, name, description, min_value, max_value, value):
-        super().__init__(name, description, None)
+    def __init__(self, name, description, min_value, max_value, value, yielding=None):
+        super().__init__(name, description, [True, False], yielding)
         self.min_value = min_value
         self.max_value = max_value
         self.set_value(value)
@@ -112,8 +118,8 @@ class UserIntegerOption(UserOption):
         return self.toint(value)
 
 class UserComboOption(UserOption):
-    def __init__(self, name, description, choices, value):
-        super().__init__(name, description, choices)
+    def __init__(self, name, description, choices, value, yielding=None):
+        super().__init__(name, description, choices, yielding)
         if not isinstance(self.choices, list):
             raise MesonException('Combo choices must be an array.')
         for i in self.choices:
@@ -134,7 +140,7 @@ class UserComboOption(UserOption):
 
 class UserArrayOption(UserOption):
     def __init__(self, name, description, value, **kwargs):
-        super().__init__(name, description, kwargs.get('choices', []))
+        super().__init__(name, description, kwargs.get('choices', []), yielding=kwargs.get('yielding', None))
         self.set_value(value, user_input=False)
 
     def validate(self, value, user_input):

mesonbuild/interpreter.py

@@ -1768,7 +1768,7 @@ external dependencies (including libraries) must go to "dependencies".''')
     def func_get_option(self, nodes, args, kwargs):
         if len(args) != 1:
             raise InterpreterException('Argument required for get_option.')
-        optname = args[0]
+        undecorated_optname = optname = args[0]
         if ':' in optname:
             raise InterpreterException('''Having a colon in option name is forbidden, projects are not allowed
 to directly access options of other subprojects.''')
@@ -1787,7 +1787,11 @@ to directly access options of other subprojects.''')
         if not coredata.is_builtin_option(optname) and self.is_subproject():
             optname = self.subproject + ':' + optname
         try:
-            return self.environment.coredata.user_options[optname].value
+            opt = self.environment.coredata.user_options[optname]
+            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)
+            return opt.value
         except KeyError:
             pass
         if optname.endswith('_link_args'):

mesonbuild/optinterpreter.py

@@ -64,16 +64,21 @@ def permitted_kwargs(permitted):
 
 optname_regex = re.compile('[^a-zA-Z0-9_-]')
 
-@permitted_kwargs({'value'})
+@permitted_kwargs({'value', 'yield'})
 def StringParser(name, description, kwargs):
-    return coredata.UserStringOption(name, description,
-                                     kwargs.get('value', ''), kwargs.get('choices', []))
+    return coredata.UserStringOption(name,
+                                     description,
+                                     kwargs.get('value', ''),
+                                     kwargs.get('choices', []),
+                                     kwargs.get('yield', coredata.default_yielding))
 
-@permitted_kwargs({'value'})
+@permitted_kwargs({'value', 'yield'})
 def BooleanParser(name, description, kwargs):
-    return coredata.UserBooleanOption(name, description, kwargs.get('value', True))
+    return coredata.UserBooleanOption(name, description,
+                                      kwargs.get('value', True),
+                                      kwargs.get('yield', coredata.default_yielding))
 
-@permitted_kwargs({'value', 'choices'})
+@permitted_kwargs({'value', 'yiel', 'choices'})
 def ComboParser(name, description, kwargs):
     if 'choices' not in kwargs:
         raise OptionException('Combo option missing "choices" keyword.')
@@ -83,9 +88,14 @@ def ComboParser(name, description, kwargs):
     for i in choices:
         if not isinstance(i, str):
             raise OptionException('Combo choice elements must be strings.')
-    return coredata.UserComboOption(name, description, choices, kwargs.get('value', choices[0]))
+    return coredata.UserComboOption(name,
+                                    description,
+                                    choices,
+                                    kwargs.get('value', choices[0]),
+                                    kwargs.get('yield', coredata.default_yielding),)
 
-@permitted_kwargs({'value', 'min', 'max'})
+
+@permitted_kwargs({'value', 'min', 'max', 'yield'})
 def IntegerParser(name, description, kwargs):
     if 'value' not in kwargs:
         raise OptionException('Integer option must contain value argument.')
@@ -93,9 +103,10 @@ def IntegerParser(name, description, kwargs):
                                       description,
                                       kwargs.get('min', None),
                                       kwargs.get('max', None),
-                                      kwargs['value'])
+                                      kwargs['value'],
+                                      kwargs.get('yield', coredata.default_yielding))
 
-@permitted_kwargs({'value', 'choices'})
+@permitted_kwargs({'value', 'yield', 'choices'})
 def string_array_parser(name, description, kwargs):
     if 'choices' in kwargs:
         choices = kwargs['choices']
@@ -110,7 +121,11 @@ def string_array_parser(name, description, kwargs):
         value = kwargs.get('value', [])
     if not isinstance(value, list):
         raise OptionException('Array choices must be passed as an array.')
-    return coredata.UserArrayOption(name, description, value, choices=choices)
+    return coredata.UserArrayOption(name,
+                                    description,
+                                    value,
+                                    choices=choices,
+                                    yielding=kwargs.get('yield', coredata.default_yielding))
 
 option_types = {'string': StringParser,
                 'boolean': BooleanParser,

test cases/common/176 yield/meson.build

@@ -0,0 +1,6 @@
+project('yield_options', 'c')
+
+subproject('sub')
+
+assert(get_option('unshared_option') == 'one', 'Unshared option has wrong value in superproject.')
+assert(get_option('shared_option') == 'two', 'Unshared option has wrong value in superproject..')

test cases/common/176 yield/meson_options.txt

@@ -0,0 +1,2 @@
+option('unshared_option', type : 'string', value : 'one')
+option('shared_option', type : 'string', value : 'two')

test cases/common/176 yield/subprojects/sub/meson.build

@@ -0,0 +1,4 @@
+project('subbie', 'c')
+
+assert(get_option('unshared_option') == 'three', 'Unshared option has wrong value in subproject.')
+assert(get_option('shared_option') == 'two', 'Shared option has wrong value in subproject.')

test cases/common/176 yield/subprojects/sub/meson_options.txt

@@ -0,0 +1,2 @@
+option('unshared_option', type : 'string', value : 'three', yield : false)
+option('shared_option', type : 'string', value : 'four', yield : true)