env.unset method

docs/markdown/snippets/environment_unset.md

@@ -0,0 +1,4 @@
+## New `unset()` method on `environment` objects
+
+[[env]] now have an [[env.unset]] method to ensure an existing environment
+is *not* defined.

docs/yaml/objects/env.yaml

@@ -82,3 +82,9 @@ methods:
     description: The values to set
 
   kwargs_inherit: env.append
+
+- name: unset
+  returns: void
+  description: |
+    Unset the specified environment variable. If this variable does not exist,
+    nothing happens.

mesonbuild/interpreter/interpreterobjects.py

@@ -285,6 +285,7 @@ class EnvironmentVariablesHolder(ObjectHolder[mesonlib.EnvironmentVariables], Mu
     def __init__(self, obj: mesonlib.EnvironmentVariables, interpreter: 'Interpreter'):
         super().__init__(obj, interpreter)
         self.methods.update({'set': self.set_method,
+                             'unset': self.unset_method,
                              'append': self.append_method,
                              'prepend': self.prepend_method,
                              })
@@ -309,6 +310,12 @@ def set_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSepara
         name, values = args
         self.held_object.set(name, values, kwargs['separator'])
 
+    @FeatureNew('environment.unset()', '1.3.0')
+    @typed_pos_args('environment.unset', str)
+    @noKwargs
+    def unset_method(self, args: T.Tuple[str], kwargs: TYPE_kwargs) -> None:
+        self.held_object.unset(args[0])
+
     @typed_pos_args('environment.append', str, varargs=str, min_varargs=1)
     @typed_kwargs('environment.append', ENV_SEPARATOR_KW)
     def append_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSeparatorKW') -> None:

mesonbuild/utils/core.py

@@ -74,6 +74,7 @@ def __init__(self, values: T.Optional[EnvInitValueType] = None,
         self.envvars: T.List[T.Tuple[T.Callable[[T.Dict[str, str], str, T.List[str], str, T.Optional[str]], str], str, T.List[str], str]] = []
         # The set of all env vars we have operations for. Only used for self.has_name()
         self.varnames: T.Set[str] = set()
+        self.unset_vars: T.Set[str] = set()
 
         if values:
             init_func = getattr(self, init_method)
@@ -103,18 +104,33 @@ def merge(self, other: EnvironmentVariables) -> None:
         for method, name, values, separator in other.envvars:
             self.varnames.add(name)
             self.envvars.append((method, name, values, separator))
+            if name in self.unset_vars:
+                self.unset_vars.remove(name)
+        self.unset_vars.update(other.unset_vars)
 
     def set(self, name: str, values: T.List[str], separator: str = os.pathsep) -> None:
         self.varnames.add(name)
         self.envvars.append((self._set, name, values, separator))
+        if name in self.unset_vars:
+            self.unset_vars.remove(name)
+
+    def unset(self, name: str) -> None:
+        if name in self.varnames:
+            self.varnames.remove(name)
+            self.envvars = [(m, n, v, s) for (m, n, v, s) in self.envvars if n != name]
+        self.unset_vars.add(name)
 
     def append(self, name: str, values: T.List[str], separator: str = os.pathsep) -> None:
         self.varnames.add(name)
         self.envvars.append((self._append, name, values, separator))
+        if name in self.unset_vars:
+            self.unset_vars.remove(name)
 
     def prepend(self, name: str, values: T.List[str], separator: str = os.pathsep) -> None:
         self.varnames.add(name)
         self.envvars.append((self._prepend, name, values, separator))
+        if name in self.unset_vars:
+            self.unset_vars.remove(name)
 
     @staticmethod
     def _set(env: T.Dict[str, str], name: str, values: T.List[str], separator: str, default_value: T.Optional[str]) -> str:
@@ -135,6 +151,8 @@ def get_env(self, full_env: EnvironOrDict, default_fmt: T.Optional[str] = None)
         for method, name, values, separator in self.envvars:
             default_value = default_fmt.format(name) if default_fmt else None
             env[name] = method(env, name, values, separator, default_value)
+        for name in self.unset_vars:
+            env.pop(name, None)
         return env