BUG: MSVCCompiler grows 'lib' & 'include' env strings exponentially.

[charris]

Each time an MSVCCompiler was instantiated the old values of

os.environ['lib'] and os.environ['include'] were concatenated to the new
values set by initializing the distutils.msvc{,9}compiler.MSVCCompiler
base class. Consequently when the the old and new values of those
variables were the same, they doubled in size with each instantiation,
leading to quickly hitting the 32,768 character limit.

This is an alternative fix for #7926. It is somewhat more involved, but imho more obviously correct than the alternatives.

[mingwandroid]

Hi @charris, by going through a set here, aren't you reordering the values?

[charris]

@mingwandroid Oh, darn. Yes, I bet so.

[charris]

I forgot that order mattered. I wonder how that applies to the order in which they were concatenated originally?

[charris]

The base class looks for the environments in the order

    HKEYS = (hkey_mod.HKEY_USERS,
             hkey_mod.HKEY_CURRENT_USER,
             hkey_mod.HKEY_LOCAL_MACHINE,
             hkey_mod.HKEY_CLASSES_ROOT)

And uses the first that exists. If that was always HKEY_CURRENT_USER we could probably dispense with the merge.

[charris]

Updated.

[mingwandroid]

Great, thanks.