[GitHub] [buildstream] abderrahim commented on issue #1360: `notparallel` variable is broken

[GitBox <gi...@apache.org>]

abderrahim commented on issue #1360:
URL: https://github.com/apache/buildstream/issues/1360#issuecomment-1015097547


   Yup, lines have shifted. The line in question is
   ```python
   self.__variables.expand(unexpanded_env)
   ```
   
   So what happens is that `Node._composite()` does a shallow copy of the nodes, then `Variables.expand()` modifies them in-place, resulting in a modified `__defaults` class variable. which is then composited into other elements with the wrong value.
   
   Here is a minimal reproducer for the issue:
   ```python
   from buildstream.node import Node
   from buildstream._variables import Variables
   
   default = Node.from_dict({'MAKEFLAGS': '-j%{max-jobs}'})
   element = Node.from_dict({'name': 'my-element.bst'})
   
   print(default, element, sep='\n')
   # [synthetic node]: {'MAKEFLAGS': '-j%{max-jobs}'}
   # [synthetic node]: {'name': 'my-element.bst'}
   
   default._composite(element)
   
   
   print(default, element, sep='\n')
   # [synthetic node]: {'MAKEFLAGS': '-j%{max-jobs}'}
   # [synthetic node]: {'name': 'my-element.bst', 'MAKEFLAGS': '-j%{max-jobs}'}
   
   v = Variables(Node.from_dict({'max-jobs': '1'}))
   v.expand(element)
   
   print(default, element, sep='\n')
   # [synthetic node]: {'MAKEFLAGS': '-j1'}
   # [synthetic node]: {'name': 'my-element.bst', 'MAKEFLAGS': '-j1'}
   ```


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