[Scons-users] Wacky crash in Clone()

[Marc Branchaud]

(Possibly should send this to scons-dev@?)

Hi all,

I'm updating a complex build from 2.2.0 (Python 2.7.18) to 4.2.0 (Python 
3.10.1), and I've run into this crash.  Unfortunately I have been unable 
to craft a simple reproduction example, and the code cannot be 
published.  The crash happens inside an env.Clone() call in a function 
being used as an Action's output, where the Action is a custom Builder.

I'm hoping someone can point out something I'm doing that became "wrong" 
since SCons 2.2.0.  Has there been a change in how custom Builders work?

Or, maybe someone can point me at someplace that might help me figure 
out the bug.

The code is basically structured as follows.  The custom builder uses 
functions from a "BaseBuilder" module defined in site_scons.  (I've 
elided a lot of setup work in the real code, which is sprinkled among 
several different files, many of which are exec()'d by the SConstruct. 
I'm trying not to suspect the reliance on exec() to split up what would 
otherwise be a giant SConstruct file.)

SConstruct
	e1 = Environment(
	    tools = [ 'MyBuilder' ],
	)
	e2 = e1.Clone(
	    CCFLAGS = ['-g']
	)
	e2.MyBuilder(
	    target="out",
	    source="in",
	)

site_scons/BaseBuilder.py
	def message(target, source, env):
	    myenv = env.Clone()           # <-- This crashes
	    print("MESSAGE")

	def builder(target, source, env):
	    print("BUILDER")

site_scons/site_tools/MyBuilder.py
	import BaseBuilder

	def exists(env):
	    return True

	def generate(env, **kwargs):
	    env['BUILDERS']['MyBuilder'] = env.Builder(
	        action = env.Action(
	            BaseBuilder.builder,
	            BaseBuilder.message,
	        )
	    )

Sadly the above code works just fine.  But here's the crash from the 
real code:

Traceback (most recent call last):
   File 
"/usr/local/lib/python3.10/site-packages/SCons-4.2.0-py3.10.egg/SCons/Taskmaster.py", 
line 235, in execute
     self.targets[0].build()
   File 
"/usr/local/lib/python3.10/site-packages/SCons-4.2.0-py3.10.egg/SCons/Node/__init__.py", 
line 755, in build
     self.get_executor()(self, **kw)
   File 
"/usr/local/lib/python3.10/site-packages/SCons-4.2.0-py3.10.egg/SCons/Executor.py", 
line 384, in __call__
     return _do_execute_map[self._do_execute](self, target, kw)
   File 
"/usr/local/lib/python3.10/site-packages/SCons-4.2.0-py3.10.egg/SCons/Executor.py", 
line 117, in execute_action_list
     status = act(*args, **kw)
   File 
"/usr/local/lib/python3.10/site-packages/SCons-4.2.0-py3.10.egg/SCons/Action.py", 
line 686, in __call__
     cmd = self.strfunction(target, source, env)
   File 
"/usr/home/marcnarc/Code/Worktrees/python3-build/site_scons/BaseBuilder.py", 
line 77, in message
     myenv = env.Clone()
   File 
"/usr/local/lib/python3.10/site-packages/SCons-4.2.0-py3.10.egg/SCons/Environment.py", 
line 1450, in Clone
     clone = copy.copy(self)
   File "/usr/local/lib/python3.10/copy.py", line 102, in copy
     return _reconstruct(x, None, *rv)
   File "/usr/local/lib/python3.10/copy.py", line 272, in _reconstruct
     if hasattr(y, '__setstate__'):
   File 
"/usr/local/lib/python3.10/site-packages/SCons-4.2.0-py3.10.egg/SCons/Environment.py", 
line 2384, in __getattr__
     attr = getattr(self.__dict__['__subject'], name)
KeyError: '__subject'

At the offending line, `self` is an OverrideEnvironment that somehow has 
a completely empty __dict__.

One frame up, the `y` that's being checked with hasattr() was created 
inside copy.copy()'s _reconstruct() via a __newobj__() call.  This `y` 
is an OverrideEnvironment but it's __dict__ is empty.

If I set a breakpoint at the dying getattr() line, it gets called twice 
before the crash, both with proper OverrideEnvironment objects.

Any ideas?  Could something in the build's code have possibly mucked 
with the OverrideEnvironment created by __newobj__()?  (What would such 
a thing even look like?)

My next step will be to bisect this using different Python and SCons 
versions.  Whee!

		M.