Add repr() for EnvironmentVariables{,Holder}

Makes it easier to debug issues with it

mesonbuild/build.py

@@ -227,6 +227,10 @@ class EnvironmentVariables:
     def __init__(self):
         self.envvars = []
 
+    def __repr__(self):
+        repr_str = "<{0}: {1}>"
+        return repr_str.format(self.__class__.__name__, self.envvars)
+
     def get_value(self, name, values, kwargs):
         separator = kwargs.get('separator', os.pathsep)
 

mesonbuild/interpreter.py

@@ -134,6 +134,10 @@ class EnvironmentVariablesHolder(MutableInterpreterObject):
                              'prepend': self.prepend_method,
                              })
 
+    def __repr__(self):
+        repr_str = "<{0}: {1}>"
+        return repr_str.format(self.__class__.__name__, self.held_object.envvars)
+
     @stringArgs
     def add_var(self, method, args, kwargs):
         if not isinstance(kwargs.get("separator", ""), str):