env.Clone() in scons doesn't do a deep-copy.

Question

In a SCons script I create a base environment from which I derived others environments. Something like this :

base = Environment()
base['CXXFLAGS'] += ['-DBOOST_HAS_PTHREAD', '-D__STDC_CONSTANT_MACROS', '-DFILELOG_MAX_LEVEL=4', '-Wall']

opt = base.Clone()
opt['CXXFLAGS'] += ['-DNDEBUG', '-O3']

This way, I can create more environment (release/debug/instrumented/pgo) from the base environment. In the SCons documentation it's said that env.Clone() does a deep copy of env. But in fact it doesn't seem to work. because in the example, the base environment would have the -DNDEBUG and -O3 flags applied.

A I doing something wrong?

edit : Here is the real code. There is two print statements in this code and I think they should print the same things, but they don't. The output follows:

# -*- coding: utf-8 -*-

import os.path
import glob

local_env = Environment()

local_env['CXXFLAGS'] += ['-DBOOST_HAS_PTHREAD', '-D__STDC_CONSTANT_MACROS', '-DFILELOG_MAX_LEVEL=4', '-Wall']
local_env.Append(LIBS = ['pthread', 'boost_thread', 'boost_filesystem', 'boost_program_options', 'boost_iostreams'])

opt = local_env.Clone()

opt['CXXFLAGS'] += ['-DNDEBUG', '-O3']

print opt['CXXFLAGS']

instr = opt.Clone()
instr['CXXFLAGS'] += ['-fprofile-arcs']
instr['LIBS'] += ['gcov']

print opt['CXXFLAGS']

The output :

|| scons: Reading SConscript files ...
|| -DBOOST_HAS_PTHREAD -D__STDC_CONSTANT_MACROS -DFILELOG_MAX_LEVEL=4 -Wall -DNDEBUG -O3
|| -DBOOST_HAS_PTHREAD -D__STDC_CONSTANT_MACROS -DFILELOG_MAX_LEVEL=4 -Wall -DNDEBUG -O3 -fprofile-arcs
|| scons: done reading SConscript files.
|| scons: Building targets ...
|| scons: `.' is up to date.
|| scons: done building targets.

Edit 2:

It's a bug with SCons http://scons.tigris.org/issues/show_bug.cgi?id=2390

Edit 3:

Will be fixed in 1.3.1 and 2.0.1

Answer 1

Assuming this is a Scons issue (code/docs discrepancy), what about adding

import copy

at the script's head, and using

opt = copy.deepcopy(Base)

i.e exploiting the fact that Scons is in Python...?

Answer 2

I faced this today, and it seems like an SCons bug. Things used to work.

Facing this on: Ubuntu 9.04 x64, Python 2.6.2, SCons v1.2.0.r3842

Presuming it is a change of API between 0.9.8 and 1.2.0 here is how to overcome it.

Was:

  e2= env.Clone()
  e2["CXXFLAGS"].remove( "-Werror" )
  e2["CXXFLAGS"].append( "-Wno-error" )

Now (1.2.0):

  import copy
  ...
  e2= env.Clone( CXXFLAGS= copy.deepcopy(env["CXXFLAGS"]) )
  e2["CXXFLAGS"].remove( "-Werror" )
  e2.AppendUnique( CXXFLAGS= "-Wno-error" )

Note that using the .Append() or .AppendUnique() methods treats the lists separately, not changing the original source. However, there does not seem to be such a method to remove a particular item from a list. This is why the '.remove()' is needed and that causes the headache.

Suggestions for easier methods or a pointer to knowing wheather this is a bug or feature of SCons 1.2.0 would be welcome.