Clarify mutable objects usage

Only Environment and ConfigurationData are mutable. However, only
ConfigurationData becomes immutable after first use which is
inconsistent.

This deprecates modification after first use of Environment object and
clarify documentation.

1 files changed, 16 insertions, 10 deletions

diff --git a/mesonbuild/interpreter/interpreterobjects.py b/mesonbuild/interpreter/interpreterobjects.py
index 5f712a573..edf785c0d 100644
--- a/mesonbuild/interpreter/interpreterobjects.py
+++ b/mesonbuild/interpreter/interpreterobjects.py
@@ -284,6 +284,7 @@ class EnvironmentVariablesHolder(ObjectHolder[mesonlib.EnvironmentVariables], Mu
 
     def __init__(self, obj: mesonlib.EnvironmentVariables, interpreter: 'Interpreter'):
         super().__init__(obj, interpreter)
+        MutableInterpreterObject.__init__(self)
         self.methods.update({'set': self.set_method,
                              'unset': self.unset_method,
                              'append': self.append_method,
@@ -308,12 +309,14 @@ class EnvironmentVariablesHolder(ObjectHolder[mesonlib.EnvironmentVariables], Mu
     @typed_kwargs('environment.set', ENV_SEPARATOR_KW)
     def set_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSeparatorKW') -> None:
         name, values = args
+        self.check_used(self.interpreter, fatal=False)
         self.held_object.set(name, values, kwargs['separator'])
 
     @FeatureNew('environment.unset', '1.4.0')
     @typed_pos_args('environment.unset', str)
     @noKwargs
     def unset_method(self, args: T.Tuple[str], kwargs: TYPE_kwargs) -> None:
+        self.check_used(self.interpreter, fatal=False)
         self.held_object.unset(args[0])
 
     @typed_pos_args('environment.append', str, varargs=str, min_varargs=1)
@@ -321,6 +324,7 @@ class EnvironmentVariablesHolder(ObjectHolder[mesonlib.EnvironmentVariables], Mu
     def append_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSeparatorKW') -> None:
         name, values = args
         self.warn_if_has_name(name)
+        self.check_used(self.interpreter, fatal=False)
         self.held_object.append(name, values, kwargs['separator'])
 
     @typed_pos_args('environment.prepend', str, varargs=str, min_varargs=1)
@@ -328,6 +332,7 @@ class EnvironmentVariablesHolder(ObjectHolder[mesonlib.EnvironmentVariables], Mu
     def prepend_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSeparatorKW') -> None:
         name, values = args
         self.warn_if_has_name(name)
+        self.check_used(self.interpreter, fatal=False)
         self.held_object.prepend(name, values, kwargs['separator'])
 
 
@@ -338,6 +343,7 @@ class ConfigurationDataHolder(ObjectHolder[build.ConfigurationData], MutableInte
 
     def __init__(self, obj: build.ConfigurationData, interpreter: 'Interpreter'):
         super().__init__(obj, interpreter)
+        MutableInterpreterObject.__init__(self)
         self.methods.update({'set': self.set_method,
                              'set10': self.set10_method,
                              'set_quoted': self.set_quoted_method,
@@ -349,32 +355,31 @@ class ConfigurationDataHolder(ObjectHolder[build.ConfigurationData], MutableInte
                              })
 
     def __deepcopy__(self, memo: T.Dict) -> 'ConfigurationDataHolder':
-        return ConfigurationDataHolder(copy.deepcopy(self.held_object), self.interpreter)
-
-    def is_used(self) -> bool:
-        return self.held_object.used
-
-    def __check_used(self) -> None:
+        obj = ConfigurationDataHolder(copy.deepcopy(self.held_object), self.interpreter)
         if self.is_used():
-            raise InterpreterException("Can not set values on configuration object that has been used.")
+            # Copies of used ConfigurationData used to be immutable. It is now
+            # allowed but we need this flag to print a FeatureNew warning if
+            # that happens.
+            obj.mutable_feature_new = True
+        return obj
 
     @typed_pos_args('configuration_data.set', str, (str, int, bool))
     @typed_kwargs('configuration_data.set', _CONF_DATA_SET_KWS)
     def set_method(self, args: T.Tuple[str, T.Union[str, int, bool]], kwargs: 'kwargs.ConfigurationDataSet') -> None:
-        self.__check_used()
+        self.check_used(self.interpreter)
         self.held_object.values[args[0]] = (args[1], kwargs['description'])
 
     @typed_pos_args('configuration_data.set_quoted', str, str)
     @typed_kwargs('configuration_data.set_quoted', _CONF_DATA_SET_KWS)
     def set_quoted_method(self, args: T.Tuple[str, str], kwargs: 'kwargs.ConfigurationDataSet') -> None:
-        self.__check_used()
+        self.check_used(self.interpreter)
         escaped_val = '\\"'.join(args[1].split('"'))
         self.held_object.values[args[0]] = (f'"{escaped_val}"', kwargs['description'])
 
     @typed_pos_args('configuration_data.set10', str, (int, bool))
     @typed_kwargs('configuration_data.set10', _CONF_DATA_SET_KWS)
     def set10_method(self, args: T.Tuple[str, T.Union[int, bool]], kwargs: 'kwargs.ConfigurationDataSet') -> None:
-        self.__check_used()
+        self.check_used(self.interpreter)
         # bool is a subclass of int, so we need to check for bool explicitly.
         # We already have typed_pos_args checking that this is either a bool or
         # an int.
@@ -437,6 +442,7 @@ class ConfigurationDataHolder(ObjectHolder[build.ConfigurationData], MutableInte
     @noKwargs
     def merge_from_method(self, args: T.Tuple[build.ConfigurationData], kwargs: TYPE_kwargs) -> None:
         from_object = args[0]
+        self.check_used(self.interpreter)
         self.held_object.values.update(from_object.values)