interpreter: copy mutable variables on assignment

All assignments in meson should be by value, so mutable objects
(i.e. environment() and configuration_data()) should be copied
automatically on assignment.

Fixes #831.

1 files changed, 10 insertions, 2 deletions

diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index 8c6e2cd..3dc0c99 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -27,6 +27,7 @@ import os, sys, subprocess, shutil, uuid, re
 from functools import wraps
 
 import importlib
+import copy
 
 run_depr_printed = False
 
@@ -91,6 +92,10 @@ class InterpreterObject():
             return self.methods[method_name](args, kwargs)
         raise InvalidCode('Unknown method "%s" in object.' % method_name)
 
+class MutableInterpreterObject(InterpreterObject):
+    def __init__(self):
+        super().__init__()
+
 class TryRunResultHolder(InterpreterObject):
     def __init__(self, res):
         super().__init__()
@@ -181,7 +186,7 @@ class ConfigureFileHolder(InterpreterObject):
         self.held_object = build.ConfigureFile(subdir, sourcename, targetname, configuration_data)
 
 
-class EnvironmentVariablesHolder(InterpreterObject):
+class EnvironmentVariablesHolder(MutableInterpreterObject):
     def __init__(self):
         super().__init__()
         self.held_object = build.EnvironmentVariables()
@@ -211,7 +216,7 @@ class EnvironmentVariablesHolder(InterpreterObject):
         self.add_var(self.held_object.prepend, args, kwargs)
 
 
-class ConfigurationDataHolder(InterpreterObject):
+class ConfigurationDataHolder(MutableInterpreterObject):
     def __init__(self):
         super().__init__()
         self.used = False # These objects become immutable after use in configure_file.
@@ -2455,6 +2460,9 @@ requirements use the version keyword argument instead.''')
         value = self.to_native(value)
         if not self.is_assignable(value):
             raise InvalidCode('Tried to assign an invalid value to variable.')
+        # 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)
         return value