Adding upstream version 1.0.1.upstream/1.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 1913 insertions, 0 deletions

diff --git a/mesonbuild/interpreterbase/__init__.py b/mesonbuild/interpreterbase/__init__.py
new file mode 100644
index 0000000..13f55e5
--- /dev/null
+++ b/mesonbuild/interpreterbase/__init__.py
@@ -0,0 +1,135 @@
+# Copyright 2013-2021 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+__all__ = [
+    'InterpreterObject',
+    'MesonInterpreterObject',
+    'ObjectHolder',
+    'IterableObject',
+    'MutableInterpreterObject',
+
+    'MesonOperator',
+
+    'Disabler',
+    'is_disabled',
+
+    'InterpreterException',
+    'InvalidCode',
+    'InvalidArguments',
+    'SubdirDoneRequest',
+    'ContinueRequest',
+    'BreakRequest',
+
+    'default_resolve_key',
+    'flatten',
+    'resolve_second_level_holders',
+
+    'noPosargs',
+    'noKwargs',
+    'stringArgs',
+    'noArgsFlattening',
+    'noSecondLevelHolderResolving',
+    'unholder_return',
+    'disablerIfNotFound',
+    'permittedKwargs',
+    'typed_operator',
+    'unary_operator',
+    'typed_pos_args',
+    'ContainerTypeInfo',
+    'KwargInfo',
+    'typed_kwargs',
+    'FeatureCheckBase',
+    'FeatureNew',
+    'FeatureDeprecated',
+    'FeatureNewKwargs',
+    'FeatureDeprecatedKwargs',
+
+    'InterpreterBase',
+
+    'SubProject',
+
+    'TV_fw_var',
+    'TV_fw_args',
+    'TV_fw_kwargs',
+    'TV_func',
+    'TYPE_elementary',
+    'TYPE_var',
+    'TYPE_nvar',
+    'TYPE_kwargs',
+    'TYPE_nkwargs',
+    'TYPE_key_resolver',
+    'TYPE_HoldableTypes',
+
+    'HoldableTypes',
+]
+
+from .baseobjects import (
+    InterpreterObject,
+    MesonInterpreterObject,
+    ObjectHolder,
+    IterableObject,
+    MutableInterpreterObject,
+
+    TV_fw_var,
+    TV_fw_args,
+    TV_fw_kwargs,
+    TV_func,
+    TYPE_elementary,
+    TYPE_var,
+    TYPE_nvar,
+    TYPE_kwargs,
+    TYPE_nkwargs,
+    TYPE_key_resolver,
+    TYPE_HoldableTypes,
+
+    SubProject,
+
+    HoldableTypes,
+)
+
+from .decorators import (
+    noPosargs,
+    noKwargs,
+    stringArgs,
+    noArgsFlattening,
+    noSecondLevelHolderResolving,
+    unholder_return,
+    disablerIfNotFound,
+    permittedKwargs,
+    typed_pos_args,
+    ContainerTypeInfo,
+    KwargInfo,
+    typed_operator,
+    unary_operator,
+    typed_kwargs,
+    FeatureCheckBase,
+    FeatureNew,
+    FeatureDeprecated,
+    FeatureNewKwargs,
+    FeatureDeprecatedKwargs,
+)
+
+from .exceptions import (
+    InterpreterException,
+    InvalidCode,
+    InvalidArguments,
+    SubdirDoneRequest,
+    ContinueRequest,
+    BreakRequest,
+)
+
+from .disabler import Disabler, is_disabled
+from .helpers import default_resolve_key, flatten, resolve_second_level_holders
+from .interpreterbase import InterpreterBase
+from .operator import MesonOperator
diff --git a/mesonbuild/interpreterbase/_unholder.py b/mesonbuild/interpreterbase/_unholder.py
new file mode 100644
index 0000000..4f1edc1
--- /dev/null
+++ b/mesonbuild/interpreterbase/_unholder.py
@@ -0,0 +1,35 @@
+# Copyright 2013-2021 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import annotations
+
+import typing as T
+
+from .baseobjects import InterpreterObject, MesonInterpreterObject, ObjectHolder, HoldableTypes
+from .exceptions import InvalidArguments
+from ..mesonlib import HoldableObject, MesonBugException
+
+if T.TYPE_CHECKING:
+    from .baseobjects import TYPE_var
+
+def _unholder(obj: InterpreterObject) -> TYPE_var:
+    if isinstance(obj, ObjectHolder):
+        assert isinstance(obj.held_object, HoldableTypes)
+        return obj.held_object
+    elif isinstance(obj, MesonInterpreterObject):
+        return obj
+    elif isinstance(obj, HoldableObject):
+        raise MesonBugException(f'Argument {obj} of type {type(obj).__name__} is not held by an ObjectHolder.')
+    elif isinstance(obj, InterpreterObject):
+        raise InvalidArguments(f'Argument {obj} of type {type(obj).__name__} cannot be passed to a method or function')
+    raise MesonBugException(f'Unknown object {obj} of type {type(obj).__name__} in the parameters.')
diff --git a/mesonbuild/interpreterbase/baseobjects.py b/mesonbuild/interpreterbase/baseobjects.py
new file mode 100644
index 0000000..820e091
--- /dev/null
+++ b/mesonbuild/interpreterbase/baseobjects.py
@@ -0,0 +1,182 @@
+# Copyright 2013-2021 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import annotations
+
+from .. import mparser
+from .exceptions import InvalidCode, InvalidArguments
+from .helpers import flatten, resolve_second_level_holders
+from .operator import MesonOperator
+from ..mesonlib import HoldableObject, MesonBugException
+import textwrap
+
+import typing as T
+from abc import ABCMeta
+
+if T.TYPE_CHECKING:
+    from typing_extensions import Protocol
+
+    # Object holders need the actual interpreter
+    from ..interpreter import Interpreter
+
+    __T = T.TypeVar('__T', bound='TYPE_var', contravariant=True)
+
+    class OperatorCall(Protocol[__T]):
+        def __call__(self, other: __T) -> 'TYPE_var': ...
+
+TV_fw_var = T.Union[str, int, bool, list, dict, 'InterpreterObject']
+TV_fw_args = T.List[T.Union[mparser.BaseNode, TV_fw_var]]
+TV_fw_kwargs = T.Dict[str, T.Union[mparser.BaseNode, TV_fw_var]]
+
+TV_func = T.TypeVar('TV_func', bound=T.Callable[..., T.Any])
+
+TYPE_elementary = T.Union[str, int, bool, T.List[T.Any], T.Dict[str, T.Any]]
+TYPE_var = T.Union[TYPE_elementary, HoldableObject, 'MesonInterpreterObject']
+TYPE_nvar = T.Union[TYPE_var, mparser.BaseNode]
+TYPE_kwargs = T.Dict[str, TYPE_var]
+TYPE_nkwargs = T.Dict[str, TYPE_nvar]
+TYPE_key_resolver = T.Callable[[mparser.BaseNode], str]
+
+SubProject = T.NewType('SubProject', str)
+
+class InterpreterObject:
+    def __init__(self, *, subproject: T.Optional['SubProject'] = None) -> None:
+        self.methods: T.Dict[
+            str,
+            T.Callable[[T.List[TYPE_var], TYPE_kwargs], TYPE_var]
+        ] = {}
+        self.operators: T.Dict[MesonOperator, 'OperatorCall'] = {}
+        self.trivial_operators: T.Dict[
+            MesonOperator,
+            T.Tuple[
+                T.Union[T.Type, T.Tuple[T.Type, ...]],
+                'OperatorCall'
+            ]
+        ] = {}
+        # Current node set during a method call. This can be used as location
+        # when printing a warning message during a method call.
+        self.current_node:  mparser.BaseNode = None
+        self.subproject = subproject or SubProject('')
+
+        # Some default operators supported by all objects
+        self.operators.update({
+            MesonOperator.EQUALS: self.op_equals,
+            MesonOperator.NOT_EQUALS: self.op_not_equals,
+        })
+
+    # The type of the object that can be printed to the user
+    def display_name(self) -> str:
+        return type(self).__name__
+
+    def method_call(
+                self,
+                method_name: str,
+                args: T.List[TYPE_var],
+                kwargs: TYPE_kwargs
+            ) -> TYPE_var:
+        if method_name in self.methods:
+            method = self.methods[method_name]
+            if not getattr(method, 'no-args-flattening', False):
+                args = flatten(args)
+            if not getattr(method, 'no-second-level-holder-flattening', False):
+                args, kwargs = resolve_second_level_holders(args, kwargs)
+            return method(args, kwargs)
+        raise InvalidCode(f'Unknown method "{method_name}" in object {self} of type {type(self).__name__}.')
+
+    def operator_call(self, operator: MesonOperator, other: TYPE_var) -> TYPE_var:
+        if operator in self.trivial_operators:
+            op = self.trivial_operators[operator]
+            if op[0] is None and other is not None:
+                raise MesonBugException(f'The unary operator `{operator.value}` of {self.display_name()} was passed the object {other} of type {type(other).__name__}')
+            if op[0] is not None and not isinstance(other, op[0]):
+                raise InvalidArguments(f'The `{operator.value}` operator of {self.display_name()} does not accept objects of type {type(other).__name__} ({other})')
+            return op[1](other)
+        if operator in self.operators:
+            return self.operators[operator](other)
+        raise InvalidCode(f'Object {self} of type {self.display_name()} does not support the `{operator.value}` operator.')
+
+    # Default comparison operator support
+    def _throw_comp_exception(self, other: TYPE_var, opt_type: str) -> T.NoReturn:
+        raise InvalidArguments(textwrap.dedent(
+            f'''
+                Trying to compare values of different types ({self.display_name()}, {type(other).__name__}) using {opt_type}.
+                This was deprecated and undefined behavior previously and is as of 0.60.0 a hard error.
+            '''
+        ))
+
+    def op_equals(self, other: TYPE_var) -> bool:
+        # We use `type(...) == type(...)` here to enforce an *exact* match for comparison. We
+        # don't want comparisons to be possible where `isinstance(derived_obj, type(base_obj))`
+        # would pass because this comparison must never be true: `derived_obj == base_obj`
+        if type(self) != type(other):
+            self._throw_comp_exception(other, '==')
+        return self == other
+
+    def op_not_equals(self, other: TYPE_var) -> bool:
+        if type(self) != type(other):
+            self._throw_comp_exception(other, '!=')
+        return self != other
+
+class MesonInterpreterObject(InterpreterObject):
+    ''' All non-elementary objects and non-object-holders should be derived from this '''
+
+class MutableInterpreterObject:
+    ''' Dummy class to mark the object type as mutable '''
+
+HoldableTypes = (HoldableObject, int, bool, str, list, dict)
+TYPE_HoldableTypes = T.Union[TYPE_elementary, HoldableObject]
+InterpreterObjectTypeVar = T.TypeVar('InterpreterObjectTypeVar', bound=TYPE_HoldableTypes)
+
+class ObjectHolder(InterpreterObject, T.Generic[InterpreterObjectTypeVar]):
+    def __init__(self, obj: InterpreterObjectTypeVar, interpreter: 'Interpreter') -> None:
+        super().__init__(subproject=interpreter.subproject)
+        # This causes some type checkers to assume that obj is a base
+        # HoldableObject, not the specialized type, so only do this assert in
+        # non-type checking situations
+        if not T.TYPE_CHECKING:
+            assert isinstance(obj, HoldableTypes), f'This is a bug: Trying to hold object of type `{type(obj).__name__}` that is not in `{HoldableTypes}`'
+        self.held_object = obj
+        self.interpreter = interpreter
+        self.env = self.interpreter.environment
+
+    # Hide the object holder abstraction from the user
+    def display_name(self) -> str:
+        return type(self.held_object).__name__
+
+    # Override default comparison operators for the held object
+    def op_equals(self, other: TYPE_var) -> bool:
+        # See the comment from InterpreterObject why we are using `type()` here.
+        if type(self.held_object) != type(other):
+            self._throw_comp_exception(other, '==')
+        return self.held_object == other
+
+    def op_not_equals(self, other: TYPE_var) -> bool:
+        if type(self.held_object) != type(other):
+            self._throw_comp_exception(other, '!=')
+        return self.held_object != other
+
+    def __repr__(self) -> str:
+        return f'<[{type(self).__name__}] holds [{type(self.held_object).__name__}]: {self.held_object!r}>'
+
+class IterableObject(metaclass=ABCMeta):
+    '''Base class for all objects that can be iterated over in a foreach loop'''
+
+    def iter_tuple_size(self) -> T.Optional[int]:
+        '''Return the size of the tuple for each iteration. Returns None if only a single value is returned.'''
+        raise MesonBugException(f'iter_tuple_size not implemented for {self.__class__.__name__}')
+
+    def iter_self(self) -> T.Iterator[T.Union[TYPE_var, T.Tuple[TYPE_var, ...]]]:
+        raise MesonBugException(f'iter not implemented for {self.__class__.__name__}')
+
+    def size(self) -> int:
+        raise MesonBugException(f'size not implemented for {self.__class__.__name__}')
diff --git a/mesonbuild/interpreterbase/decorators.py b/mesonbuild/interpreterbase/decorators.py
new file mode 100644
index 0000000..173cedc
--- /dev/null
+++ b/mesonbuild/interpreterbase/decorators.py
@@ -0,0 +1,791 @@
+# Copyright 2013-2021 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import annotations
+
+from .. import mesonlib, mlog
+from .disabler import Disabler
+from .exceptions import InterpreterException, InvalidArguments
+from ._unholder import _unholder
+
+from dataclasses import dataclass
+from functools import wraps
+import abc
+import itertools
+import copy
+import typing as T
+
+if T.TYPE_CHECKING:
+    from typing_extensions import Protocol
+
+    from .. import mparser
+    from .baseobjects import InterpreterObject, TV_func, TYPE_var, TYPE_kwargs
+    from .interpreterbase import SubProject
+    from .operator import MesonOperator
+
+    _TV_IntegerObject = T.TypeVar('_TV_IntegerObject', bound=InterpreterObject, contravariant=True)
+    _TV_ARG1 = T.TypeVar('_TV_ARG1', bound=TYPE_var, contravariant=True)
+
+    class FN_Operator(Protocol[_TV_IntegerObject, _TV_ARG1]):
+        def __call__(s, self: _TV_IntegerObject, other: _TV_ARG1) -> TYPE_var: ...
+    _TV_FN_Operator = T.TypeVar('_TV_FN_Operator', bound=FN_Operator)
+
+def get_callee_args(wrapped_args: T.Sequence[T.Any]) -> T.Tuple['mparser.BaseNode', T.List['TYPE_var'], 'TYPE_kwargs', 'SubProject']:
+    # First argument could be InterpreterBase, InterpreterObject or ModuleObject.
+    # In the case of a ModuleObject it is the 2nd argument (ModuleState) that
+    # contains the needed information.
+    s = wrapped_args[0]
+    if not hasattr(s, 'current_node'):
+        s = wrapped_args[1]
+    node = s.current_node
+    subproject = s.subproject
+    args = kwargs = None
+    if len(wrapped_args) >= 3:
+        args = wrapped_args[-2]
+        kwargs = wrapped_args[-1]
+    return node, args, kwargs, subproject
+
+def noPosargs(f: TV_func) -> TV_func:
+    @wraps(f)
+    def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+        args = get_callee_args(wrapped_args)[1]
+        if args:
+            raise InvalidArguments('Function does not take positional arguments.')
+        return f(*wrapped_args, **wrapped_kwargs)
+    return T.cast('TV_func', wrapped)
+
+def noKwargs(f: TV_func) -> TV_func:
+    @wraps(f)
+    def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+        kwargs = get_callee_args(wrapped_args)[2]
+        if kwargs:
+            raise InvalidArguments('Function does not take keyword arguments.')
+        return f(*wrapped_args, **wrapped_kwargs)
+    return T.cast('TV_func', wrapped)
+
+def stringArgs(f: TV_func) -> TV_func:
+    @wraps(f)
+    def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+        args = get_callee_args(wrapped_args)[1]
+        if not isinstance(args, list):
+            mlog.debug('Not a list:', str(args))
+            raise InvalidArguments('Argument not a list.')
+        if not all(isinstance(s, str) for s in args):
+            mlog.debug('Element not a string:', str(args))
+            raise InvalidArguments('Arguments must be strings.')
+        return f(*wrapped_args, **wrapped_kwargs)
+    return T.cast('TV_func', wrapped)
+
+def noArgsFlattening(f: TV_func) -> TV_func:
+    setattr(f, 'no-args-flattening', True)  # noqa: B010
+    return f
+
+def noSecondLevelHolderResolving(f: TV_func) -> TV_func:
+    setattr(f, 'no-second-level-holder-flattening', True)  # noqa: B010
+    return f
+
+def unholder_return(f: TV_func) -> T.Callable[..., TYPE_var]:
+    @wraps(f)
+    def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+        res = f(*wrapped_args, **wrapped_kwargs)
+        return _unholder(res)
+    return T.cast('T.Callable[..., TYPE_var]', wrapped)
+
+def disablerIfNotFound(f: TV_func) -> TV_func:
+    @wraps(f)
+    def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+        kwargs = get_callee_args(wrapped_args)[2]
+        disabler = kwargs.pop('disabler', False)
+        ret = f(*wrapped_args, **wrapped_kwargs)
+        if disabler and not ret.found():
+            return Disabler()
+        return ret
+    return T.cast('TV_func', wrapped)
+
+@dataclass(repr=False, eq=False)
+class permittedKwargs:
+    permitted: T.Set[str]
+
+    def __call__(self, f: TV_func) -> TV_func:
+        @wraps(f)
+        def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+            kwargs = get_callee_args(wrapped_args)[2]
+            unknowns = set(kwargs).difference(self.permitted)
+            if unknowns:
+                ustr = ', '.join([f'"{u}"' for u in sorted(unknowns)])
+                raise InvalidArguments(f'Got unknown keyword arguments {ustr}')
+            return f(*wrapped_args, **wrapped_kwargs)
+        return T.cast('TV_func', wrapped)
+
+def typed_operator(operator: MesonOperator,
+                   types: T.Union[T.Type, T.Tuple[T.Type, ...]]) -> T.Callable[['_TV_FN_Operator'], '_TV_FN_Operator']:
+    """Decorator that does type checking for operator calls.
+
+    The principle here is similar to typed_pos_args, however much simpler
+    since only one other object ever is passed
+    """
+    def inner(f: '_TV_FN_Operator') -> '_TV_FN_Operator':
+        @wraps(f)
+        def wrapper(self: 'InterpreterObject', other: TYPE_var) -> TYPE_var:
+            if not isinstance(other, types):
+                raise InvalidArguments(f'The `{operator.value}` of {self.display_name()} does not accept objects of type {type(other).__name__} ({other})')
+            return f(self, other)
+        return T.cast('_TV_FN_Operator', wrapper)
+    return inner
+
+def unary_operator(operator: MesonOperator) -> T.Callable[['_TV_FN_Operator'], '_TV_FN_Operator']:
+    """Decorator that does type checking for unary operator calls.
+
+    This decorator is for unary operators that do not take any other objects.
+    It should be impossible for a user to accidentally break this. Triggering
+    this check always indicates a bug in the Meson interpreter.
+    """
+    def inner(f: '_TV_FN_Operator') -> '_TV_FN_Operator':
+        @wraps(f)
+        def wrapper(self: 'InterpreterObject', other: TYPE_var) -> TYPE_var:
+            if other is not None:
+                raise mesonlib.MesonBugException(f'The unary operator `{operator.value}` of {self.display_name()} was passed the object {other} of type {type(other).__name__}')
+            return f(self, other)
+        return T.cast('_TV_FN_Operator', wrapper)
+    return inner
+
+
+def typed_pos_args(name: str, *types: T.Union[T.Type, T.Tuple[T.Type, ...]],
+                   varargs: T.Optional[T.Union[T.Type, T.Tuple[T.Type, ...]]] = None,
+                   optargs: T.Optional[T.List[T.Union[T.Type, T.Tuple[T.Type, ...]]]] = None,
+                   min_varargs: int = 0, max_varargs: int = 0) -> T.Callable[..., T.Any]:
+    """Decorator that types type checking of positional arguments.
+
+    This supports two different models of optional arguments, the first is the
+    variadic argument model. Variadic arguments are a possibly bounded,
+    possibly unbounded number of arguments of the same type (unions are
+    supported). The second is the standard default value model, in this case
+    a number of optional arguments may be provided, but they are still
+    ordered, and they may have different types.
+
+    This function does not support mixing variadic and default arguments.
+
+    :name: The name of the decorated function (as displayed in error messages)
+    :varargs: They type(s) of any variadic arguments the function takes. If
+        None the function takes no variadic args
+    :min_varargs: the minimum number of variadic arguments taken
+    :max_varargs: the maximum number of variadic arguments taken. 0 means unlimited
+    :optargs: The types of any optional arguments parameters taken. If None
+        then no optional parameters are taken.
+
+    Some examples of usage blow:
+    >>> @typed_pos_args('mod.func', str, (str, int))
+    ... def func(self, state: ModuleState, args: T.Tuple[str, T.Union[str, int]], kwargs: T.Dict[str, T.Any]) -> T.Any:
+    ...     pass
+
+    >>> @typed_pos_args('method', str, varargs=str)
+    ... def method(self, node: BaseNode, args: T.Tuple[str, T.List[str]], kwargs: T.Dict[str, T.Any]) -> T.Any:
+    ...     pass
+
+    >>> @typed_pos_args('method', varargs=str, min_varargs=1)
+    ... def method(self, node: BaseNode, args: T.Tuple[T.List[str]], kwargs: T.Dict[str, T.Any]) -> T.Any:
+    ...     pass
+
+    >>> @typed_pos_args('method', str, optargs=[(str, int), str])
+    ... def method(self, node: BaseNode, args: T.Tuple[str, T.Optional[T.Union[str, int]], T.Optional[str]], kwargs: T.Dict[str, T.Any]) -> T.Any:
+    ...     pass
+
+    When should you chose `typed_pos_args('name', varargs=str,
+    min_varargs=1)` vs `typed_pos_args('name', str, varargs=str)`?
+
+    The answer has to do with the semantics of the function, if all of the
+    inputs are the same type (such as with `files()`) then the former is
+    correct, all of the arguments are string names of files. If the first
+    argument is something else the it should be separated.
+    """
+    def inner(f: TV_func) -> TV_func:
+
+        @wraps(f)
+        def wrapper(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+            args = get_callee_args(wrapped_args)[1]
+
+            # These are implementation programming errors, end users should never see them.
+            assert isinstance(args, list), args
+            assert max_varargs >= 0, 'max_varags cannot be negative'
+            assert min_varargs >= 0, 'min_varags cannot be negative'
+            assert optargs is None or varargs is None, \
+                'varargs and optargs not supported together as this would be ambiguous'
+
+            num_args = len(args)
+            num_types = len(types)
+            a_types = types
+
+            if varargs:
+                min_args = num_types + min_varargs
+                max_args = num_types + max_varargs
+                if max_varargs == 0 and num_args < min_args:
+                    raise InvalidArguments(f'{name} takes at least {min_args} arguments, but got {num_args}.')
+                elif max_varargs != 0 and (num_args < min_args or num_args > max_args):
+                    raise InvalidArguments(f'{name} takes between {min_args} and {max_args} arguments, but got {num_args}.')
+            elif optargs:
+                if num_args < num_types:
+                    raise InvalidArguments(f'{name} takes at least {num_types} arguments, but got {num_args}.')
+                elif num_args > num_types + len(optargs):
+                    raise InvalidArguments(f'{name} takes at most {num_types + len(optargs)} arguments, but got {num_args}.')
+                # Add the number of positional arguments required
+                if num_args > num_types:
+                    diff = num_args - num_types
+                    a_types = tuple(list(types) + list(optargs[:diff]))
+            elif num_args != num_types:
+                raise InvalidArguments(f'{name} takes exactly {num_types} arguments, but got {num_args}.')
+
+            for i, (arg, type_) in enumerate(itertools.zip_longest(args, a_types, fillvalue=varargs), start=1):
+                if not isinstance(arg, type_):
+                    if isinstance(type_, tuple):
+                        shouldbe = 'one of: {}'.format(", ".join(f'"{t.__name__}"' for t in type_))
+                    else:
+                        shouldbe = f'"{type_.__name__}"'
+                    raise InvalidArguments(f'{name} argument {i} was of type "{type(arg).__name__}" but should have been {shouldbe}')
+
+            # Ensure that we're actually passing a tuple.
+            # Depending on what kind of function we're calling the length of
+            # wrapped_args can vary.
+            nargs = list(wrapped_args)
+            i = nargs.index(args)
+            if varargs:
+                # if we have varargs we need to split them into a separate
+                # tuple, as python's typing doesn't understand tuples with
+                # fixed elements and variadic elements, only one or the other.
+                # so in that case we need T.Tuple[int, str, float, T.Tuple[str, ...]]
+                pos = args[:len(types)]
+                var = list(args[len(types):])
+                pos.append(var)
+                nargs[i] = tuple(pos)
+            elif optargs:
+                if num_args < num_types + len(optargs):
+                    diff = num_types + len(optargs) - num_args
+                    nargs[i] = tuple(list(args) + [None] * diff)
+                else:
+                    nargs[i] = args
+            else:
+                nargs[i] = tuple(args)
+            return f(*nargs, **wrapped_kwargs)
+
+        return T.cast('TV_func', wrapper)
+    return inner
+
+
+class ContainerTypeInfo:
+
+    """Container information for keyword arguments.
+
+    For keyword arguments that are containers (list or dict), this class encodes
+    that information.
+
+    :param container: the type of container
+    :param contains: the types the container holds
+    :param pairs: if the container is supposed to be of even length.
+        This is mainly used for interfaces that predate the addition of dictionaries, and use
+        `[key, value, key2, value2]` format.
+    :param allow_empty: Whether this container is allowed to be empty
+        There are some cases where containers not only must be passed, but must
+        not be empty, and other cases where an empty container is allowed.
+    """
+
+    def __init__(self, container: T.Type, contains: T.Union[T.Type, T.Tuple[T.Type, ...]], *,
+                 pairs: bool = False, allow_empty: bool = True):
+        self.container = container
+        self.contains = contains
+        self.pairs = pairs
+        self.allow_empty = allow_empty
+
+    def check(self, value: T.Any) -> bool:
+        """Check that a value is valid.
+
+        :param value: A value to check
+        :return: True if it is valid, False otherwise
+        """
+        if not isinstance(value, self.container):
+            return False
+        iter_ = iter(value.values()) if isinstance(value, dict) else iter(value)
+        for each in iter_:
+            if not isinstance(each, self.contains):
+                return False
+        if self.pairs and len(value) % 2 != 0:
+            return False
+        if not value and not self.allow_empty:
+            return False
+        return True
+
+    def description(self) -> str:
+        """Human readable description of this container type.
+
+        :return: string to be printed
+        """
+        container = 'dict' if self.container is dict else 'array'
+        if isinstance(self.contains, tuple):
+            contains = ' | '.join([t.__name__ for t in self.contains])
+        else:
+            contains = self.contains.__name__
+        s = f'{container}[{contains}]'
+        if self.pairs:
+            s += ' that has even size'
+        if not self.allow_empty:
+            s += ' that cannot be empty'
+        return s
+
+_T = T.TypeVar('_T')
+
+class _NULL_T:
+    """Special null type for evolution, this is an implementation detail."""
+
+
+_NULL = _NULL_T()
+
+class KwargInfo(T.Generic[_T]):
+
+    """A description of a keyword argument to a meson function
+
+    This is used to describe a value to the :func:typed_kwargs function.
+
+    :param name: the name of the parameter
+    :param types: A type or tuple of types that are allowed, or a :class:ContainerType
+    :param required: Whether this is a required keyword argument. defaults to False
+    :param listify: If true, then the argument will be listified before being
+        checked. This is useful for cases where the Meson DSL allows a scalar or
+        a container, but internally we only want to work with containers
+    :param default: A default value to use if this isn't set. defaults to None,
+        this may be safely set to a mutable type, as long as that type does not
+        itself contain mutable types, typed_kwargs will copy the default
+    :param since: Meson version in which this argument has been added. defaults to None
+    :param since_message: An extra message to pass to FeatureNew when since is triggered
+    :param deprecated: Meson version in which this argument has been deprecated. defaults to None
+    :param deprecated_message: An extra message to pass to FeatureDeprecated
+        when since is triggered
+    :param validator: A callable that does additional validation. This is mainly
+        intended for cases where a string is expected, but only a few specific
+        values are accepted. Must return None if the input is valid, or a
+        message if the input is invalid
+    :param convertor: A callable that converts the raw input value into a
+        different type. This is intended for cases such as the meson DSL using a
+        string, but the implementation using an Enum. This should not do
+        validation, just conversion.
+    :param deprecated_values: a dictionary mapping a value to the version of
+        meson it was deprecated in. The Value may be any valid value for this
+        argument.
+    :param since_values: a dictionary mapping a value to the version of meson it was
+        added in.
+    :param not_set_warning: A warning message that is logged if the kwarg is not
+        set by the user.
+    :param feature_validator: A callable returning an iterable of FeatureNew | FeatureDeprecated objects.
+    """
+    def __init__(self, name: str,
+                 types: T.Union[T.Type[_T], T.Tuple[T.Union[T.Type[_T], ContainerTypeInfo], ...], ContainerTypeInfo],
+                 *, required: bool = False, listify: bool = False,
+                 default: T.Optional[_T] = None,
+                 since: T.Optional[str] = None,
+                 since_message: T.Optional[str] = None,
+                 since_values: T.Optional[T.Dict[T.Union[_T, T.Type[T.List], T.Type[T.Dict]], T.Union[str, T.Tuple[str, str]]]] = None,
+                 deprecated: T.Optional[str] = None,
+                 deprecated_message: T.Optional[str] = None,
+                 deprecated_values: T.Optional[T.Dict[T.Union[_T, T.Type[T.List], T.Type[T.Dict]], T.Union[str, T.Tuple[str, str]]]] = None,
+                 feature_validator: T.Optional[T.Callable[[_T], T.Iterable[FeatureCheckBase]]] = None,
+                 validator: T.Optional[T.Callable[[T.Any], T.Optional[str]]] = None,
+                 convertor: T.Optional[T.Callable[[_T], object]] = None,
+                 not_set_warning: T.Optional[str] = None):
+        self.name = name
+        self.types = types
+        self.required = required
+        self.listify = listify
+        self.default = default
+        self.since = since
+        self.since_message = since_message
+        self.since_values = since_values
+        self.feature_validator = feature_validator
+        self.deprecated = deprecated
+        self.deprecated_message = deprecated_message
+        self.deprecated_values = deprecated_values
+        self.validator = validator
+        self.convertor = convertor
+        self.not_set_warning = not_set_warning
+
+    def evolve(self, *,
+               name: T.Union[str, _NULL_T] = _NULL,
+               required: T.Union[bool, _NULL_T] = _NULL,
+               listify: T.Union[bool, _NULL_T] = _NULL,
+               default: T.Union[_T, None, _NULL_T] = _NULL,
+               since: T.Union[str, None, _NULL_T] = _NULL,
+               since_message: T.Union[str, None, _NULL_T] = _NULL,
+               since_values: T.Union[T.Dict[T.Union[_T, T.Type[T.List], T.Type[T.Dict]], T.Union[str, T.Tuple[str, str]]], None, _NULL_T] = _NULL,
+               deprecated: T.Union[str, None, _NULL_T] = _NULL,
+               deprecated_message: T.Union[str, None, _NULL_T] = _NULL,
+               deprecated_values: T.Union[T.Dict[T.Union[_T, T.Type[T.List], T.Type[T.Dict]], T.Union[str, T.Tuple[str, str]]], None, _NULL_T] = _NULL,
+               feature_validator: T.Union[T.Callable[[_T], T.Iterable[FeatureCheckBase]], None, _NULL_T] = _NULL,
+               validator: T.Union[T.Callable[[_T], T.Optional[str]], None, _NULL_T] = _NULL,
+               convertor: T.Union[T.Callable[[_T], TYPE_var], None, _NULL_T] = _NULL) -> 'KwargInfo':
+        """Create a shallow copy of this KwargInfo, with modifications.
+
+        This allows us to create a new copy of a KwargInfo with modifications.
+        This allows us to use a shared kwarg that implements complex logic, but
+        has slight differences in usage, such as being added to different
+        functions in different versions of Meson.
+
+        The use the _NULL special value here allows us to pass None, which has
+        meaning in many of these cases. _NULL itself is never stored, always
+        being replaced by either the copy in self, or the provided new version.
+        """
+        return type(self)(
+            name if not isinstance(name, _NULL_T) else self.name,
+            self.types,
+            listify=listify if not isinstance(listify, _NULL_T) else self.listify,
+            required=required if not isinstance(required, _NULL_T) else self.required,
+            default=default if not isinstance(default, _NULL_T) else self.default,
+            since=since if not isinstance(since, _NULL_T) else self.since,
+            since_message=since_message if not isinstance(since_message, _NULL_T) else self.since_message,
+            since_values=since_values if not isinstance(since_values, _NULL_T) else self.since_values,
+            deprecated=deprecated if not isinstance(deprecated, _NULL_T) else self.deprecated,
+            deprecated_message=deprecated_message if not isinstance(deprecated_message, _NULL_T) else self.deprecated_message,
+            deprecated_values=deprecated_values if not isinstance(deprecated_values, _NULL_T) else self.deprecated_values,
+            feature_validator=feature_validator if not isinstance(feature_validator, _NULL_T) else self.feature_validator,
+            validator=validator if not isinstance(validator, _NULL_T) else self.validator,
+            convertor=convertor if not isinstance(convertor, _NULL_T) else self.convertor,
+        )
+
+
+def typed_kwargs(name: str, *types: KwargInfo, allow_unknown: bool = False) -> T.Callable[..., T.Any]:
+    """Decorator for type checking keyword arguments.
+
+    Used to wrap a meson DSL implementation function, where it checks various
+    things about keyword arguments, including the type, and various other
+    information. For non-required values it sets the value to a default, which
+    means the value will always be provided.
+
+    If type tyhpe is a :class:ContainerTypeInfo, then the default value will be
+    passed as an argument to the container initializer, making a shallow copy
+
+    :param name: the name of the function, including the object it's attached to
+        (if applicable)
+    :param *types: KwargInfo entries for each keyword argument.
+    """
+    def inner(f: TV_func) -> TV_func:
+
+        def types_description(types_tuple: T.Tuple[T.Union[T.Type, ContainerTypeInfo], ...]) -> str:
+            candidates = []
+            for t in types_tuple:
+                if isinstance(t, ContainerTypeInfo):
+                    candidates.append(t.description())
+                else:
+                    candidates.append(t.__name__)
+            shouldbe = 'one of: ' if len(candidates) > 1 else ''
+            shouldbe += ', '.join(candidates)
+            return shouldbe
+
+        def raw_description(t: object) -> str:
+            """describe a raw type (ie, one that is not a ContainerTypeInfo)."""
+            if isinstance(t, list):
+                if t:
+                    return f"array[{' | '.join(sorted(mesonlib.OrderedSet(type(v).__name__ for v in t)))}]"
+                return 'array[]'
+            elif isinstance(t, dict):
+                if t:
+                    return f"dict[{' | '.join(sorted(mesonlib.OrderedSet(type(v).__name__ for v in t.values())))}]"
+                return 'dict[]'
+            return type(t).__name__
+
+        def check_value_type(types_tuple: T.Tuple[T.Union[T.Type, ContainerTypeInfo], ...],
+                             value: T.Any) -> bool:
+            for t in types_tuple:
+                if isinstance(t, ContainerTypeInfo):
+                    if t.check(value):
+                        return True
+                elif isinstance(value, t):
+                    return True
+            return False
+
+        @wraps(f)
+        def wrapper(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+
+            def emit_feature_change(values: T.Dict[_T, T.Union[str, T.Tuple[str, str]]], feature: T.Union[T.Type['FeatureDeprecated'], T.Type['FeatureNew']]) -> None:
+                for n, version in values.items():
+                    warn = False
+                    if isinstance(version, tuple):
+                        version, msg = version
+                    else:
+                        msg = None
+
+                    if n in {dict, list}:
+                        assert isinstance(n, type), 'for mypy'
+                        if isinstance(value, n):
+                            feature.single_use(f'"{name}" keyword argument "{info.name}" of type {n.__name__}', version, subproject, msg, location=node)
+                    elif isinstance(value, (dict, list)):
+                        warn = n in value
+                    else:
+                        warn = n == value
+
+                    if warn:
+                        feature.single_use(f'"{name}" keyword argument "{info.name}" value "{n}"', version, subproject, msg, location=node)
+
+            node, _, _kwargs, subproject = get_callee_args(wrapped_args)
+            # Cast here, as the convertor function may place something other than a TYPE_var in the kwargs
+            kwargs = T.cast('T.Dict[str, object]', _kwargs)
+
+            if not allow_unknown:
+                all_names = {t.name for t in types}
+                unknowns = set(kwargs).difference(all_names)
+                if unknowns:
+                    ustr = ', '.join([f'"{u}"' for u in sorted(unknowns)])
+                    raise InvalidArguments(f'{name} got unknown keyword arguments {ustr}')
+
+            for info in types:
+                types_tuple = info.types if isinstance(info.types, tuple) else (info.types,)
+                value = kwargs.get(info.name)
+                if value is not None:
+                    if info.since:
+                        feature_name = info.name + ' arg in ' + name
+                        FeatureNew.single_use(feature_name, info.since, subproject, info.since_message, location=node)
+                    if info.deprecated:
+                        feature_name = info.name + ' arg in ' + name
+                        FeatureDeprecated.single_use(feature_name, info.deprecated, subproject, info.deprecated_message, location=node)
+                    if info.listify:
+                        kwargs[info.name] = value = mesonlib.listify(value)
+                    if not check_value_type(types_tuple, value):
+                        shouldbe = types_description(types_tuple)
+                        raise InvalidArguments(f'{name} keyword argument {info.name!r} was of type {raw_description(value)} but should have been {shouldbe}')
+
+                    if info.validator is not None:
+                        msg = info.validator(value)
+                        if msg is not None:
+                            raise InvalidArguments(f'{name} keyword argument "{info.name}" {msg}')
+
+                    if info.feature_validator is not None:
+                        for each in info.feature_validator(value):
+                            each.use(subproject, node)
+
+                    if info.deprecated_values is not None:
+                        emit_feature_change(info.deprecated_values, FeatureDeprecated)
+
+                    if info.since_values is not None:
+                        emit_feature_change(info.since_values, FeatureNew)
+
+                elif info.required:
+                    raise InvalidArguments(f'{name} is missing required keyword argument "{info.name}"')
+                else:
+                    # set the value to the default, this ensuring all kwargs are present
+                    # This both simplifies the typing checking and the usage
+                    assert check_value_type(types_tuple, info.default), f'In funcion {name} default value of {info.name} is not a valid type, got {type(info.default)} expected {types_description(types_tuple)}'
+                    # Create a shallow copy of the container. This allows mutable
+                    # types to be used safely as default values
+                    kwargs[info.name] = copy.copy(info.default)
+                    if info.not_set_warning:
+                        mlog.warning(info.not_set_warning)
+
+                if info.convertor:
+                    kwargs[info.name] = info.convertor(kwargs[info.name])
+
+            return f(*wrapped_args, **wrapped_kwargs)
+        return T.cast('TV_func', wrapper)
+    return inner
+
+
+# This cannot be a dataclass due to https://github.com/python/mypy/issues/5374
+class FeatureCheckBase(metaclass=abc.ABCMeta):
+    "Base class for feature version checks"
+
+    feature_registry: T.ClassVar[T.Dict[str, T.Dict[str, T.Set[T.Tuple[str, T.Optional['mparser.BaseNode']]]]]]
+    emit_notice = False
+
+    def __init__(self, feature_name: str, feature_version: str, extra_message: str = ''):
+        self.feature_name = feature_name  # type: str
+        self.feature_version = feature_version    # type: str
+        self.extra_message = extra_message  # type: str
+
+    @staticmethod
+    def get_target_version(subproject: str) -> str:
+        # Don't do any checks if project() has not been parsed yet
+        if subproject not in mesonlib.project_meson_versions:
+            return ''
+        return mesonlib.project_meson_versions[subproject]
+
+    @staticmethod
+    @abc.abstractmethod
+    def check_version(target_version: str, feature_version: str) -> bool:
+        pass
+
+    def use(self, subproject: 'SubProject', location: T.Optional['mparser.BaseNode'] = None) -> None:
+        tv = self.get_target_version(subproject)
+        # No target version
+        if tv == '':
+            return
+        # Target version is new enough, don't warn
+        if self.check_version(tv, self.feature_version) and not self.emit_notice:
+            return
+        # Feature is too new for target version or we want to emit notices, register it
+        if subproject not in self.feature_registry:
+            self.feature_registry[subproject] = {self.feature_version: set()}
+        register = self.feature_registry[subproject]
+        if self.feature_version not in register:
+            register[self.feature_version] = set()
+
+        feature_key = (self.feature_name, location)
+        if feature_key in register[self.feature_version]:
+            # Don't warn about the same feature multiple times
+            # FIXME: This is needed to prevent duplicate warnings, but also
+            # means we won't warn about a feature used in multiple places.
+            return
+        register[self.feature_version].add(feature_key)
+        # Target version is new enough, don't warn even if it is registered for notice
+        if self.check_version(tv, self.feature_version):
+            return
+        self.log_usage_warning(tv, location)
+
+    @classmethod
+    def report(cls, subproject: str) -> None:
+        if subproject not in cls.feature_registry:
+            return
+        warning_str = cls.get_warning_str_prefix(cls.get_target_version(subproject))
+        notice_str = cls.get_notice_str_prefix(cls.get_target_version(subproject))
+        fv = cls.feature_registry[subproject]
+        tv = cls.get_target_version(subproject)
+        for version in sorted(fv.keys()):
+            if cls.check_version(tv, version):
+                notice_str += '\n * {}: {}'.format(version, {i[0] for i in fv[version]})
+            else:
+                warning_str += '\n * {}: {}'.format(version, {i[0] for i in fv[version]})
+        if '\n' in notice_str:
+            mlog.notice(notice_str, fatal=False)
+        if '\n' in warning_str:
+            mlog.warning(warning_str)
+
+    def log_usage_warning(self, tv: str, location: T.Optional['mparser.BaseNode']) -> None:
+        raise InterpreterException('log_usage_warning not implemented')
+
+    @staticmethod
+    def get_warning_str_prefix(tv: str) -> str:
+        raise InterpreterException('get_warning_str_prefix not implemented')
+
+    @staticmethod
+    def get_notice_str_prefix(tv: str) -> str:
+        raise InterpreterException('get_notice_str_prefix not implemented')
+
+    def __call__(self, f: TV_func) -> TV_func:
+        @wraps(f)
+        def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+            node, _, _, subproject = get_callee_args(wrapped_args)
+            if subproject is None:
+                raise AssertionError(f'{wrapped_args!r}')
+            self.use(subproject, node)
+            return f(*wrapped_args, **wrapped_kwargs)
+        return T.cast('TV_func', wrapped)
+
+    @classmethod
+    def single_use(cls, feature_name: str, version: str, subproject: 'SubProject',
+                   extra_message: str = '', location: T.Optional['mparser.BaseNode'] = None) -> None:
+        """Oneline version that instantiates and calls use()."""
+        cls(feature_name, version, extra_message).use(subproject, location)
+
+
+class FeatureNew(FeatureCheckBase):
+    """Checks for new features"""
+
+    # Class variable, shared across all instances
+    #
+    # Format: {subproject: {feature_version: set(feature_names)}}
+    feature_registry = {}  # type: T.ClassVar[T.Dict[str, T.Dict[str, T.Set[T.Tuple[str, T.Optional[mparser.BaseNode]]]]]]
+
+    @staticmethod
+    def check_version(target_version: str, feature_version: str) -> bool:
+        return mesonlib.version_compare_condition_with_min(target_version, feature_version)
+
+    @staticmethod
+    def get_warning_str_prefix(tv: str) -> str:
+        return f'Project specifies a minimum meson_version \'{tv}\' but uses features which were added in newer versions:'
+
+    @staticmethod
+    def get_notice_str_prefix(tv: str) -> str:
+        return ''
+
+    def log_usage_warning(self, tv: str, location: T.Optional['mparser.BaseNode']) -> None:
+        args = [
+            'Project targets', f"'{tv}'",
+            'but uses feature introduced in',
+            f"'{self.feature_version}':",
+            f'{self.feature_name}.',
+        ]
+        if self.extra_message:
+            args.append(self.extra_message)
+        mlog.warning(*args, location=location)
+
+class FeatureDeprecated(FeatureCheckBase):
+    """Checks for deprecated features"""
+
+    # Class variable, shared across all instances
+    #
+    # Format: {subproject: {feature_version: set(feature_names)}}
+    feature_registry = {}  # type: T.ClassVar[T.Dict[str, T.Dict[str, T.Set[T.Tuple[str, T.Optional[mparser.BaseNode]]]]]]
+    emit_notice = True
+
+    @staticmethod
+    def check_version(target_version: str, feature_version: str) -> bool:
+        # For deprecation checks we need to return the inverse of FeatureNew checks
+        return not mesonlib.version_compare_condition_with_min(target_version, feature_version)
+
+    @staticmethod
+    def get_warning_str_prefix(tv: str) -> str:
+        return 'Deprecated features used:'
+
+    @staticmethod
+    def get_notice_str_prefix(tv: str) -> str:
+        return 'Future-deprecated features used:'
+
+    def log_usage_warning(self, tv: str, location: T.Optional['mparser.BaseNode']) -> None:
+        args = [
+            'Project targets', f"'{tv}'",
+            'but uses feature deprecated since',
+            f"'{self.feature_version}':",
+            f'{self.feature_name}.',
+        ]
+        if self.extra_message:
+            args.append(self.extra_message)
+        mlog.warning(*args, location=location)
+
+
+# This cannot be a dataclass due to https://github.com/python/mypy/issues/5374
+class FeatureCheckKwargsBase(metaclass=abc.ABCMeta):
+
+    @property
+    @abc.abstractmethod
+    def feature_check_class(self) -> T.Type[FeatureCheckBase]:
+        pass
+
+    def __init__(self, feature_name: str, feature_version: str,
+                 kwargs: T.List[str], extra_message: T.Optional[str] = None):
+        self.feature_name = feature_name
+        self.feature_version = feature_version
+        self.kwargs = kwargs
+        self.extra_message = extra_message
+
+    def __call__(self, f: TV_func) -> TV_func:
+        @wraps(f)
+        def wrapped(*wrapped_args: T.Any, **wrapped_kwargs: T.Any) -> T.Any:
+            node, _, kwargs, subproject = get_callee_args(wrapped_args)
+            if subproject is None:
+                raise AssertionError(f'{wrapped_args!r}')
+            for arg in self.kwargs:
+                if arg not in kwargs:
+                    continue
+                name = arg + ' arg in ' + self.feature_name
+                self.feature_check_class.single_use(
+                        name, self.feature_version, subproject, self.extra_message, node)
+            return f(*wrapped_args, **wrapped_kwargs)
+        return T.cast('TV_func', wrapped)
+
+class FeatureNewKwargs(FeatureCheckKwargsBase):
+    feature_check_class = FeatureNew
+
+class FeatureDeprecatedKwargs(FeatureCheckKwargsBase):
+    feature_check_class = FeatureDeprecated
diff --git a/mesonbuild/interpreterbase/disabler.py b/mesonbuild/interpreterbase/disabler.py
new file mode 100644
index 0000000..182bb62
--- /dev/null
+++ b/mesonbuild/interpreterbase/disabler.py
@@ -0,0 +1,45 @@
+# Copyright 2013-2021 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import annotations
+
+import typing as T
+
+from .baseobjects import MesonInterpreterObject
+
+if T.TYPE_CHECKING:
+    from .baseobjects import TYPE_var, TYPE_kwargs
+
+class Disabler(MesonInterpreterObject):
+    def method_call(self, method_name: str, args: T.List[TYPE_var], kwargs: TYPE_kwargs) -> TYPE_var:
+        if method_name == 'found':
+            return False
+        return Disabler()
+
+def _is_arg_disabled(arg: T.Any) -> bool:
+    if isinstance(arg, Disabler):
+        return True
+    if isinstance(arg, list):
+        for i in arg:
+            if _is_arg_disabled(i):
+                return True
+    return False
+
+def is_disabled(args: T.Sequence[T.Any], kwargs: T.Dict[str, T.Any]) -> bool:
+    for i in args:
+        if _is_arg_disabled(i):
+            return True
+    for i in kwargs.values():
+        if _is_arg_disabled(i):
+            return True
+    return False
diff --git a/mesonbuild/interpreterbase/exceptions.py b/mesonbuild/interpreterbase/exceptions.py
new file mode 100644
index 0000000..cdbe0fb
--- /dev/null
+++ b/mesonbuild/interpreterbase/exceptions.py
@@ -0,0 +1,33 @@
+# Copyright 2013-2021 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ..mesonlib import MesonException
+
+class InterpreterException(MesonException):
+    pass
+
+class InvalidCode(InterpreterException):
+    pass
+
+class InvalidArguments(InterpreterException):
+    pass
+
+class SubdirDoneRequest(BaseException):
+    pass
+
+class ContinueRequest(BaseException):
+    pass
+
+class BreakRequest(BaseException):
+    pass
diff --git a/mesonbuild/interpreterbase/helpers.py b/mesonbuild/interpreterbase/helpers.py
new file mode 100644
index 0000000..2196b4e
--- /dev/null
+++ b/mesonbuild/interpreterbase/helpers.py
@@ -0,0 +1,56 @@
+# Copyright 2013-2021 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from __future__ import annotations
+
+from .. import mesonlib, mparser
+from .exceptions import InterpreterException
+
+import collections.abc
+import typing as T
+
+if T.TYPE_CHECKING:
+    from .baseobjects import TYPE_var, TYPE_kwargs
+
+def flatten(args: T.Union['TYPE_var', T.List['TYPE_var']]) -> T.List['TYPE_var']:
+    if isinstance(args, mparser.StringNode):
+        assert isinstance(args.value, str)
+        return [args.value]
+    if not isinstance(args, collections.abc.Sequence):
+        return [args]
+    result: T.List['TYPE_var'] = []
+    for a in args:
+        if isinstance(a, list):
+            rest = flatten(a)
+            result = result + rest
+        elif isinstance(a, mparser.StringNode):
+            result.append(a.value)
+        else:
+            result.append(a)
+    return result
+
+def resolve_second_level_holders(args: T.List['TYPE_var'], kwargs: 'TYPE_kwargs') -> T.Tuple[T.List['TYPE_var'], 'TYPE_kwargs']:
+    def resolver(arg: 'TYPE_var') -> 'TYPE_var':
+        if isinstance(arg, list):
+            return [resolver(x) for x in arg]
+        if isinstance(arg, dict):
+            return {k: resolver(v) for k, v in arg.items()}
+        if isinstance(arg, mesonlib.SecondLevelHolder):
+            return arg.get_default_object()
+        return arg
+    return [resolver(x) for x in args], {k: resolver(v) for k, v in kwargs.items()}
+
+def default_resolve_key(key: mparser.BaseNode) -> str:
+    if not isinstance(key, mparser.IdNode):
+        raise InterpreterException('Invalid kwargs format.')
+    return key.value
diff --git a/mesonbuild/interpreterbase/interpreterbase.py b/mesonbuild/interpreterbase/interpreterbase.py
new file mode 100644
index 0000000..f72ddc1
--- /dev/null
+++ b/mesonbuild/interpreterbase/interpreterbase.py
@@ -0,0 +1,604 @@
+# Copyright 2016-2017 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.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This class contains the basic functionality needed to run any interpreter
+# or an interpreter-based tool.
+from __future__ import annotations
+
+from .. import mparser, mesonlib
+from .. import environment
+
+from .baseobjects import (
+    InterpreterObject,
+    MesonInterpreterObject,
+    MutableInterpreterObject,
+    InterpreterObjectTypeVar,
+    ObjectHolder,
+    IterableObject,
+
+    HoldableTypes,
+)
+
+from .exceptions import (
+    InterpreterException,
+    InvalidCode,
+    InvalidArguments,
+    SubdirDoneRequest,
+    ContinueRequest,
+    BreakRequest
+)
+
+from .decorators import FeatureNew
+from .disabler import Disabler, is_disabled
+from .helpers import default_resolve_key, flatten, resolve_second_level_holders
+from .operator import MesonOperator
+from ._unholder import _unholder
+
+import os, copy, re, pathlib
+import typing as T
+import textwrap
+
+if T.TYPE_CHECKING:
+    from .baseobjects import SubProject, TYPE_kwargs, TYPE_var
+    from ..interpreter import Interpreter
+
+    HolderMapType = T.Dict[
+        T.Union[
+            T.Type[mesonlib.HoldableObject],
+            T.Type[int],
+            T.Type[bool],
+            T.Type[str],
+            T.Type[list],
+            T.Type[dict],
+        ],
+        # For some reason, this has to be a callable and can't just be ObjectHolder[InterpreterObjectTypeVar]
+        T.Callable[[InterpreterObjectTypeVar, 'Interpreter'], ObjectHolder[InterpreterObjectTypeVar]]
+    ]
+
+    FunctionType = T.Dict[
+        str,
+        T.Callable[[mparser.BaseNode, T.List[TYPE_var], T.Dict[str, TYPE_var]], TYPE_var]
+    ]
+
+class InterpreterBase:
+    def __init__(self, source_root: str, subdir: str, subproject: 'SubProject'):
+        self.source_root = source_root
+        self.funcs: FunctionType = {}
+        self.builtin: T.Dict[str, InterpreterObject] = {}
+        # Holder maps store a mapping from an HoldableObject to a class ObjectHolder
+        self.holder_map: HolderMapType = {}
+        self.bound_holder_map: HolderMapType = {}
+        self.subdir = subdir
+        self.root_subdir = subdir
+        self.subproject = subproject
+        self.variables: T.Dict[str, InterpreterObject] = {}
+        self.argument_depth = 0
+        self.current_lineno = -1
+        # Current node set during a function call. This can be used as location
+        # when printing a warning message during a method call.
+        self.current_node = None  # type: mparser.BaseNode
+        # This is set to `version_string` when this statement is evaluated:
+        # meson.version().compare_version(version_string)
+        # If it was part of a if-clause, it is used to temporally override the
+        # current meson version target within that if-block.
+        self.tmp_meson_version = None # type: T.Optional[str]
+
+    def load_root_meson_file(self) -> None:
+        mesonfile = os.path.join(self.source_root, self.subdir, environment.build_filename)
+        if not os.path.isfile(mesonfile):
+            raise InvalidArguments(f'Missing Meson file in {mesonfile}')
+        with open(mesonfile, encoding='utf-8') as mf:
+            code = mf.read()
+        if code.isspace():
+            raise InvalidCode('Builder file is empty.')
+        assert isinstance(code, str)
+        try:
+            self.ast = mparser.Parser(code, mesonfile).parse()
+        except mesonlib.MesonException as me:
+            me.file = mesonfile
+            raise me
+
+    def parse_project(self) -> None:
+        """
+        Parses project() and initializes languages, compilers etc. Do this
+        early because we need this before we parse the rest of the AST.
+        """
+        self.evaluate_codeblock(self.ast, end=1)
+
+    def sanity_check_ast(self) -> None:
+        if not isinstance(self.ast, mparser.CodeBlockNode):
+            raise InvalidCode('AST is of invalid type. Possibly a bug in the parser.')
+        if not self.ast.lines:
+            raise InvalidCode('No statements in code.')
+        first = self.ast.lines[0]
+        if not isinstance(first, mparser.FunctionNode) or first.func_name != 'project':
+            p = pathlib.Path(self.source_root).resolve()
+            found = p
+            for parent in p.parents:
+                if (parent / 'meson.build').is_file():
+                    with open(parent / 'meson.build', encoding='utf-8') as f:
+                        if f.readline().startswith('project('):
+                            found = parent
+                            break
+                else:
+                    break
+
+            error = 'first statement must be a call to project()'
+            if found != p:
+                raise InvalidCode(f'Not the project root: {error}\n\nDid you mean to run meson from the directory: "{found}"?')
+            else:
+                raise InvalidCode(f'Invalid source tree: {error}')
+
+    def run(self) -> None:
+        # Evaluate everything after the first line, which is project() because
+        # we already parsed that in self.parse_project()
+        try:
+            self.evaluate_codeblock(self.ast, start=1)
+        except SubdirDoneRequest:
+            pass
+
+    def evaluate_codeblock(self, node: mparser.CodeBlockNode, start: int = 0, end: T.Optional[int] = None) -> None:
+        if node is None:
+            return
+        if not isinstance(node, mparser.CodeBlockNode):
+            e = InvalidCode('Tried to execute a non-codeblock. Possibly a bug in the parser.')
+            e.lineno = node.lineno
+            e.colno = node.colno
+            raise e
+        statements = node.lines[start:end]
+        i = 0
+        while i < len(statements):
+            cur = statements[i]
+            try:
+                self.current_lineno = cur.lineno
+                self.evaluate_statement(cur)
+            except Exception as e:
+                if getattr(e, 'lineno', None) is None:
+                    # We are doing the equivalent to setattr here and mypy does not like it
+                    e.lineno = cur.lineno                                                             # type: ignore
+                    e.colno = cur.colno                                                               # type: ignore
+                    e.file = os.path.join(self.source_root, self.subdir, environment.build_filename)  # type: ignore
+                raise e
+            i += 1 # In THE FUTURE jump over blocks and stuff.
+
+    def evaluate_statement(self, cur: mparser.BaseNode) -> T.Optional[InterpreterObject]:
+        self.current_node = cur
+        if isinstance(cur, mparser.FunctionNode):
+            return self.function_call(cur)
+        elif isinstance(cur, mparser.AssignmentNode):
+            self.assignment(cur)
+        elif isinstance(cur, mparser.MethodNode):
+            return self.method_call(cur)
+        elif isinstance(cur, mparser.StringNode):
+            return self._holderify(cur.value)
+        elif isinstance(cur, mparser.BooleanNode):
+            return self._holderify(cur.value)
+        elif isinstance(cur, mparser.IfClauseNode):
+            return self.evaluate_if(cur)
+        elif isinstance(cur, mparser.IdNode):
+            return self.get_variable(cur.value)
+        elif isinstance(cur, mparser.ComparisonNode):
+            return self.evaluate_comparison(cur)
+        elif isinstance(cur, mparser.ArrayNode):
+            return self.evaluate_arraystatement(cur)
+        elif isinstance(cur, mparser.DictNode):
+            return self.evaluate_dictstatement(cur)
+        elif isinstance(cur, mparser.NumberNode):
+            return self._holderify(cur.value)
+        elif isinstance(cur, mparser.AndNode):
+            return self.evaluate_andstatement(cur)
+        elif isinstance(cur, mparser.OrNode):
+            return self.evaluate_orstatement(cur)
+        elif isinstance(cur, mparser.NotNode):
+            return self.evaluate_notstatement(cur)
+        elif isinstance(cur, mparser.UMinusNode):
+            return self.evaluate_uminusstatement(cur)
+        elif isinstance(cur, mparser.ArithmeticNode):
+            return self.evaluate_arithmeticstatement(cur)
+        elif isinstance(cur, mparser.ForeachClauseNode):
+            self.evaluate_foreach(cur)
+        elif isinstance(cur, mparser.PlusAssignmentNode):
+            self.evaluate_plusassign(cur)
+        elif isinstance(cur, mparser.IndexNode):
+            return self.evaluate_indexing(cur)
+        elif isinstance(cur, mparser.TernaryNode):
+            return self.evaluate_ternary(cur)
+        elif isinstance(cur, mparser.FormatStringNode):
+            if isinstance(cur, mparser.MultilineFormatStringNode):
+                return self.evaluate_multiline_fstring(cur)
+            else:
+                return self.evaluate_fstring(cur)
+        elif isinstance(cur, mparser.ContinueNode):
+            raise ContinueRequest()
+        elif isinstance(cur, mparser.BreakNode):
+            raise BreakRequest()
+        else:
+            raise InvalidCode("Unknown statement.")
+        return None
+
+    def evaluate_arraystatement(self, cur: mparser.ArrayNode) -> InterpreterObject:
+        (arguments, kwargs) = self.reduce_arguments(cur.args)
+        if len(kwargs) > 0:
+            raise InvalidCode('Keyword arguments are invalid in array construction.')
+        return self._holderify([_unholder(x) for x in arguments])
+
+    @FeatureNew('dict', '0.47.0')
+    def evaluate_dictstatement(self, cur: mparser.DictNode) -> InterpreterObject:
+        def resolve_key(key: mparser.BaseNode) -> str:
+            if not isinstance(key, mparser.StringNode):
+                FeatureNew.single_use('Dictionary entry using non literal key', '0.53.0', self.subproject)
+            str_key = _unholder(self.evaluate_statement(key))
+            if not isinstance(str_key, str):
+                raise InvalidArguments('Key must be a string')
+            return str_key
+        arguments, kwargs = self.reduce_arguments(cur.args, key_resolver=resolve_key, duplicate_key_error='Duplicate dictionary key: {}')
+        assert not arguments
+        return self._holderify({k: _unholder(v) for k, v in kwargs.items()})
+
+    def evaluate_notstatement(self, cur: mparser.NotNode) -> InterpreterObject:
+        v = self.evaluate_statement(cur.value)
+        if isinstance(v, Disabler):
+            return v
+        return self._holderify(v.operator_call(MesonOperator.NOT, None))
+
+    def evaluate_if(self, node: mparser.IfClauseNode) -> T.Optional[Disabler]:
+        assert isinstance(node, mparser.IfClauseNode)
+        for i in node.ifs:
+            # Reset self.tmp_meson_version to know if it gets set during this
+            # statement evaluation.
+            self.tmp_meson_version = None
+            result = self.evaluate_statement(i.condition)
+            if isinstance(result, Disabler):
+                return result
+            if not isinstance(result, InterpreterObject):
+                raise mesonlib.MesonBugException(f'Argument to not ({result}) is not an InterpreterObject but {type(result).__name__}.')
+            res = result.operator_call(MesonOperator.BOOL, None)
+            if not isinstance(res, bool):
+                raise InvalidCode(f'If clause {result!r} does not evaluate to true or false.')
+            if res:
+                prev_meson_version = mesonlib.project_meson_versions[self.subproject]
+                if self.tmp_meson_version:
+                    mesonlib.project_meson_versions[self.subproject] = self.tmp_meson_version
+                try:
+                    self.evaluate_codeblock(i.block)
+                finally:
+                    mesonlib.project_meson_versions[self.subproject] = prev_meson_version
+                return None
+        if not isinstance(node.elseblock, mparser.EmptyNode):
+            self.evaluate_codeblock(node.elseblock)
+        return None
+
+    def evaluate_comparison(self, node: mparser.ComparisonNode) -> InterpreterObject:
+        val1 = self.evaluate_statement(node.left)
+        if isinstance(val1, Disabler):
+            return val1
+        val2 = self.evaluate_statement(node.right)
+        if isinstance(val2, Disabler):
+            return val2
+
+        # New code based on InterpreterObjects
+        operator = {
+            'in': MesonOperator.IN,
+            'notin': MesonOperator.NOT_IN,
+            '==': MesonOperator.EQUALS,
+            '!=': MesonOperator.NOT_EQUALS,
+            '>': MesonOperator.GREATER,
+            '<': MesonOperator.LESS,
+            '>=': MesonOperator.GREATER_EQUALS,
+            '<=': MesonOperator.LESS_EQUALS,
+        }[node.ctype]
+
+        # Check if the arguments should be reversed for simplicity (this essentially converts `in` to `contains`)
+        if operator in (MesonOperator.IN, MesonOperator.NOT_IN):
+            val1, val2 = val2, val1
+
+        val1.current_node = node
+        return self._holderify(val1.operator_call(operator, _unholder(val2)))
+
+    def evaluate_andstatement(self, cur: mparser.AndNode) -> InterpreterObject:
+        l = self.evaluate_statement(cur.left)
+        if isinstance(l, Disabler):
+            return l
+        l_bool = l.operator_call(MesonOperator.BOOL, None)
+        if not l_bool:
+            return self._holderify(l_bool)
+        r = self.evaluate_statement(cur.right)
+        if isinstance(r, Disabler):
+            return r
+        return self._holderify(r.operator_call(MesonOperator.BOOL, None))
+
+    def evaluate_orstatement(self, cur: mparser.OrNode) -> InterpreterObject:
+        l = self.evaluate_statement(cur.left)
+        if isinstance(l, Disabler):
+            return l
+        l_bool = l.operator_call(MesonOperator.BOOL, None)
+        if l_bool:
+            return self._holderify(l_bool)
+        r = self.evaluate_statement(cur.right)
+        if isinstance(r, Disabler):
+            return r
+        return self._holderify(r.operator_call(MesonOperator.BOOL, None))
+
+    def evaluate_uminusstatement(self, cur: mparser.UMinusNode) -> InterpreterObject:
+        v = self.evaluate_statement(cur.value)
+        if isinstance(v, Disabler):
+            return v
+        v.current_node = cur
+        return self._holderify(v.operator_call(MesonOperator.UMINUS, None))
+
+    def evaluate_arithmeticstatement(self, cur: mparser.ArithmeticNode) -> InterpreterObject:
+        l = self.evaluate_statement(cur.left)
+        if isinstance(l, Disabler):
+            return l
+        r = self.evaluate_statement(cur.right)
+        if isinstance(r, Disabler):
+            return r
+
+        mapping: T.Dict[str, MesonOperator] = {
+            'add': MesonOperator.PLUS,
+            'sub': MesonOperator.MINUS,
+            'mul': MesonOperator.TIMES,
+            'div': MesonOperator.DIV,
+            'mod': MesonOperator.MOD,
+        }
+        l.current_node = cur
+        res = l.operator_call(mapping[cur.operation], _unholder(r))
+        return self._holderify(res)
+
+    def evaluate_ternary(self, node: mparser.TernaryNode) -> T.Optional[InterpreterObject]:
+        assert isinstance(node, mparser.TernaryNode)
+        result = self.evaluate_statement(node.condition)
+        if isinstance(result, Disabler):
+            return result
+        result.current_node = node
+        result_bool = result.operator_call(MesonOperator.BOOL, None)
+        if result_bool:
+            return self.evaluate_statement(node.trueblock)
+        else:
+            return self.evaluate_statement(node.falseblock)
+
+    @FeatureNew('multiline format strings', '0.63.0')
+    def evaluate_multiline_fstring(self, node: mparser.MultilineFormatStringNode) -> InterpreterObject:
+        return self.evaluate_fstring(node)
+
+    @FeatureNew('format strings', '0.58.0')
+    def evaluate_fstring(self, node: mparser.FormatStringNode) -> InterpreterObject:
+        assert isinstance(node, mparser.FormatStringNode)
+
+        def replace(match: T.Match[str]) -> str:
+            var = str(match.group(1))
+            try:
+                val = _unholder(self.variables[var])
+                if not isinstance(val, (str, int, float, bool)):
+                    raise InvalidCode(f'Identifier "{var}" does not name a formattable variable ' +
+                                      '(has to be an integer, a string, a floating point number or a boolean).')
+
+                return str(val)
+            except KeyError:
+                raise InvalidCode(f'Identifier "{var}" does not name a variable.')
+
+        res = re.sub(r'@([_a-zA-Z][_0-9a-zA-Z]*)@', replace, node.value)
+        return self._holderify(res)
+
+    def evaluate_foreach(self, node: mparser.ForeachClauseNode) -> None:
+        assert isinstance(node, mparser.ForeachClauseNode)
+        items = self.evaluate_statement(node.items)
+        if not isinstance(items, IterableObject):
+            raise InvalidArguments('Items of foreach loop do not support iterating')
+
+        tsize = items.iter_tuple_size()
+        if len(node.varnames) != (tsize or 1):
+            raise InvalidArguments(f'Foreach expects exactly {tsize or 1} variables for iterating over objects of type {items.display_name()}')
+
+        for i in items.iter_self():
+            if tsize is None:
+                if isinstance(i, tuple):
+                    raise mesonlib.MesonBugException(f'Iteration of {items} returned a tuple even though iter_tuple_size() is None')
+                self.set_variable(node.varnames[0], self._holderify(i))
+            else:
+                if not isinstance(i, tuple):
+                    raise mesonlib.MesonBugException(f'Iteration of {items} did not return a tuple even though iter_tuple_size() is {tsize}')
+                if len(i) != tsize:
+                    raise mesonlib.MesonBugException(f'Iteration of {items} did not return a tuple even though iter_tuple_size() is {tsize}')
+                for j in range(tsize):
+                    self.set_variable(node.varnames[j], self._holderify(i[j]))
+            try:
+                self.evaluate_codeblock(node.block)
+            except ContinueRequest:
+                continue
+            except BreakRequest:
+                break
+
+    def evaluate_plusassign(self, node: mparser.PlusAssignmentNode) -> None:
+        assert isinstance(node, mparser.PlusAssignmentNode)
+        varname = node.var_name
+        addition = self.evaluate_statement(node.value)
+
+        # Remember that all variables are immutable. We must always create a
+        # full new variable and then assign it.
+        old_variable = self.get_variable(varname)
+        old_variable.current_node = node
+        new_value = self._holderify(old_variable.operator_call(MesonOperator.PLUS, _unholder(addition)))
+        self.set_variable(varname, new_value)
+
+    def evaluate_indexing(self, node: mparser.IndexNode) -> InterpreterObject:
+        assert isinstance(node, mparser.IndexNode)
+        iobject = self.evaluate_statement(node.iobject)
+        if isinstance(iobject, Disabler):
+            return iobject
+        index = _unholder(self.evaluate_statement(node.index))
+
+        if iobject is None:
+            raise InterpreterException('Tried to evaluate indexing on None')
+        iobject.current_node = node
+        return self._holderify(iobject.operator_call(MesonOperator.INDEX, index))
+
+    def function_call(self, node: mparser.FunctionNode) -> T.Optional[InterpreterObject]:
+        func_name = node.func_name
+        (h_posargs, h_kwargs) = self.reduce_arguments(node.args)
+        (posargs, kwargs) = self._unholder_args(h_posargs, h_kwargs)
+        if is_disabled(posargs, kwargs) and func_name not in {'get_variable', 'set_variable', 'unset_variable', 'is_disabler'}:
+            return Disabler()
+        if func_name in self.funcs:
+            func = self.funcs[func_name]
+            func_args = posargs
+            if not getattr(func, 'no-args-flattening', False):
+                func_args = flatten(posargs)
+            if not getattr(func, 'no-second-level-holder-flattening', False):
+                func_args, kwargs = resolve_second_level_holders(func_args, kwargs)
+            res = func(node, func_args, kwargs)
+            return self._holderify(res) if res is not None else None
+        else:
+            self.unknown_function_called(func_name)
+            return None
+
+    def method_call(self, node: mparser.MethodNode) -> T.Optional[InterpreterObject]:
+        invokable = node.source_object
+        obj: T.Optional[InterpreterObject]
+        if isinstance(invokable, mparser.IdNode):
+            object_display_name = f'variable "{invokable.value}"'
+            obj = self.get_variable(invokable.value)
+        else:
+            object_display_name = invokable.__class__.__name__
+            obj = self.evaluate_statement(invokable)
+        method_name = node.name
+        (h_args, h_kwargs) = self.reduce_arguments(node.args)
+        (args, kwargs) = self._unholder_args(h_args, h_kwargs)
+        if is_disabled(args, kwargs):
+            return Disabler()
+        if not isinstance(obj, InterpreterObject):
+            raise InvalidArguments(f'{object_display_name} is not callable.')
+        # TODO: InterpreterBase **really** shouldn't be in charge of checking this
+        if method_name == 'extract_objects':
+            if isinstance(obj, ObjectHolder):
+                self.validate_extraction(obj.held_object)
+            elif not isinstance(obj, Disabler):
+                raise InvalidArguments(f'Invalid operation "extract_objects" on {object_display_name} of type {type(obj).__name__}')
+        obj.current_node = node
+        res = obj.method_call(method_name, args, kwargs)
+        return self._holderify(res) if res is not None else None
+
+    def _holderify(self, res: T.Union[TYPE_var, InterpreterObject]) -> InterpreterObject:
+        if isinstance(res, HoldableTypes):
+            # Always check for an exact match first.
+            cls = self.holder_map.get(type(res), None)
+            if cls is not None:
+                # Casts to Interpreter are required here since an assertion would
+                # not work for the `ast` module.
+                return cls(res, T.cast('Interpreter', self))
+            # Try the boundary types next.
+            for typ, cls in self.bound_holder_map.items():
+                if isinstance(res, typ):
+                    return cls(res, T.cast('Interpreter', self))
+            raise mesonlib.MesonBugException(f'Object {res} of type {type(res).__name__} is neither in self.holder_map nor self.bound_holder_map.')
+        elif isinstance(res, ObjectHolder):
+            raise mesonlib.MesonBugException(f'Returned object {res} of type {type(res).__name__} is an object holder.')
+        elif isinstance(res, MesonInterpreterObject):
+            return res
+        raise mesonlib.MesonBugException(f'Unknown returned object {res} of type {type(res).__name__} in the parameters.')
+
+    def _unholder_args(self,
+                       args: T.List[InterpreterObject],
+                       kwargs: T.Dict[str, InterpreterObject]) -> T.Tuple[T.List[TYPE_var], TYPE_kwargs]:
+        return [_unholder(x) for x in args], {k: _unholder(v) for k, v in kwargs.items()}
+
+    def unknown_function_called(self, func_name: str) -> None:
+        raise InvalidCode(f'Unknown function "{func_name}".')
+
+    def reduce_arguments(
+                self,
+                args: mparser.ArgumentNode,
+                key_resolver: T.Callable[[mparser.BaseNode], str] = default_resolve_key,
+                duplicate_key_error: T.Optional[str] = None,
+            ) -> T.Tuple[
+                T.List[InterpreterObject],
+                T.Dict[str, InterpreterObject]
+            ]:
+        assert isinstance(args, mparser.ArgumentNode)
+        if args.incorrect_order():
+            raise InvalidArguments('All keyword arguments must be after positional arguments.')
+        self.argument_depth += 1
+        reduced_pos = [self.evaluate_statement(arg) for arg in args.arguments]
+        if any(x is None for x in reduced_pos):
+            raise InvalidArguments('At least one value in the arguments is void.')
+        reduced_kw: T.Dict[str, InterpreterObject] = {}
+        for key, val in args.kwargs.items():
+            reduced_key = key_resolver(key)
+            assert isinstance(val, mparser.BaseNode)
+            reduced_val = self.evaluate_statement(val)
+            if reduced_val is None:
+                raise InvalidArguments(f'Value of key {reduced_key} is void.')
+            if duplicate_key_error and reduced_key in reduced_kw:
+                raise InvalidArguments(duplicate_key_error.format(reduced_key))
+            reduced_kw[reduced_key] = reduced_val
+        self.argument_depth -= 1
+        final_kw = self.expand_default_kwargs(reduced_kw)
+        return reduced_pos, final_kw
+
+    def expand_default_kwargs(self, kwargs: T.Dict[str, T.Optional[InterpreterObject]]) -> T.Dict[str, T.Optional[InterpreterObject]]:
+        if 'kwargs' not in kwargs:
+            return kwargs
+        to_expand = _unholder(kwargs.pop('kwargs'))
+        if not isinstance(to_expand, dict):
+            raise InterpreterException('Value of "kwargs" must be dictionary.')
+        if 'kwargs' in to_expand:
+            raise InterpreterException('Kwargs argument must not contain a "kwargs" entry. Points for thinking meta, though. :P')
+        for k, v in to_expand.items():
+            if k in kwargs:
+                raise InterpreterException(f'Entry "{k}" defined both as a keyword argument and in a "kwarg" entry.')
+            kwargs[k] = self._holderify(v)
+        return kwargs
+
+    def assignment(self, node: mparser.AssignmentNode) -> None:
+        assert isinstance(node, mparser.AssignmentNode)
+        if self.argument_depth != 0:
+            raise InvalidArguments(textwrap.dedent('''\
+                Tried to assign values inside an argument list.
+                To specify a keyword argument, use : instead of =.
+            '''))
+        var_name = node.var_name
+        if not isinstance(var_name, str):
+            raise InvalidArguments('Tried to assign value to a non-variable.')
+        value = self.evaluate_statement(node.value)
+        # For mutable objects we need to make a copy on assignment
+        if isinstance(value, MutableInterpreterObject):
+            value = copy.deepcopy(value)
+        self.set_variable(var_name, value)
+
+    def set_variable(self, varname: str, variable: T.Union[TYPE_var, InterpreterObject], *, holderify: bool = False) -> None:
+        if variable is None:
+            raise InvalidCode('Can not assign None to variable.')
+        if holderify:
+            variable = self._holderify(variable)
+        else:
+            # Ensure that we are always storing ObjectHolders
+            if not isinstance(variable, InterpreterObject):
+                raise mesonlib.MesonBugException(f'set_variable in InterpreterBase called with a non InterpreterObject {variable} of type {type(variable).__name__}')
+        if not isinstance(varname, str):
+            raise InvalidCode('First argument to set_variable must be a string.')
+        if re.match('[_a-zA-Z][_0-9a-zA-Z]*$', varname) is None:
+            raise InvalidCode('Invalid variable name: ' + varname)
+        if varname in self.builtin:
+            raise InvalidCode(f'Tried to overwrite internal variable "{varname}"')
+        self.variables[varname] = variable
+
+    def get_variable(self, varname: str) -> InterpreterObject:
+        if varname in self.builtin:
+            return self.builtin[varname]
+        if varname in self.variables:
+            return self.variables[varname]
+        raise InvalidCode(f'Unknown variable "{varname}".')
+
+    def validate_extraction(self, buildtarget: mesonlib.HoldableObject) -> None:
+        raise InterpreterException('validate_extraction is not implemented in this context (please file a bug)')
diff --git a/mesonbuild/interpreterbase/operator.py b/mesonbuild/interpreterbase/operator.py
new file mode 100644
index 0000000..5dec8d0
--- /dev/null
+++ b/mesonbuild/interpreterbase/operator.py
@@ -0,0 +1,32 @@
+# SPDX-license-identifier: Apache-2.0
+
+from enum import Enum
+
+class MesonOperator(Enum):
+    # Arithmetic
+    PLUS = '+'
+    MINUS = '-'
+    TIMES = '*'
+    DIV = '/'
+    MOD = '%'
+
+    UMINUS = 'uminus'
+
+    # Logic
+    NOT = 'not'
+
+    # Should return the boolsche interpretation of the value (`'' == false` for instance)
+    BOOL = 'bool()'
+
+    # Comparison
+    EQUALS = '=='
+    NOT_EQUALS = '!='
+    GREATER = '>'
+    LESS = '<'
+    GREATER_EQUALS = '>='
+    LESS_EQUALS = '<='
+
+    # Container
+    IN = 'in'
+    NOT_IN = 'not in'
+    INDEX = '[]'