[Distutils] Why doesn't distutils respect the INCLUDE/LIB en vironment variable (MSVC)?

[Moore, Paul]

From: M.-A. Lemburg [mailto:mal@lemburg.com]
> I don't know about the convention for looking up parameters
> on Windows: do env vars override settings in the registry
> or the other way around ?

I just checked. It's actually worse than I thought. The environment
variables are the *only* thing that affect the command-line tools. The
registry is purely for the IDE, I guess. So what distutils is doing, rather
than being unhelpful, is actually wrong...

It *is* possible to install Visual C++ in such a way that the environment
variables are not set by default, leaving the user to run a BAT file to set
them up before the command line tools are usable. It's possible that the
distutils approach is to cater for such users, by registering the
appropriate variables even if VCVARS32.BAT has not been run.

> Depending on what the standard procedure is on Windows, I'd
> suggest to either prepend or append the env var settings to the 
> LIB/INCLUDE values found through the registry.

Based on the above, I'd suggest not grubbing through the registry at all -
just leave things as the user has them. Or to handle the case where the user
hasn't set the environment variables, maybe check whether INCLUDE is set -
if not, either prompt the user (probably better, as VCVARS32.BAT definitely
does the right thing), or grub through the registry in that case only.

A bare minimum patch (which just leaves the vars if set, otherwise works as
at present) could be (UNTESTED):

--- msvccompiler.py.orig	Thu Apr 19 10:24:24 2001
+++ msvccompiler.py	Mon Jul 16 14:02:05 2001
@@ -155,8 +155,11 @@
 def set_path_env_var (name, version_number):
     """Set environment variable 'name' to an MSVC path type value obtained
        from 'get_msvc_paths()'.  This is equivalent to a SET command prior
-       to execution of spawned commands."""
+       to execution of spawned commands.  If the environment variable is
+       already set, leave it alone."""
 
+    if os.environ.has_key(name)
+        return
     p = get_msvc_paths (name, version_number)
     if p:
         os.environ[name] = string.join (p,';')

Paul.