AppendUnique breaks CPPScanner when using defs without value

[Inviz]

AppendUnique turns string values into tuples with single values, breaking dictify_CPPDEFINES, and thus CPPScanner.

Details of my investigation here: https://community.platformio.org/t/libraries-included-inside-conditional-guard-are-still-added-to-the-dep-graph-by-ldf/26326/4

1. Platformio inside its ProcessFlags parses defs like -DA -DB=C into ('A', ('B', 'C')) for env[“CPPDEFINES”]
2. libopencm3.py script tries to add -DSTM32F4 def via env.ApppendUnique(CPPDEFINES=["STM32F4"]) (which is not really necessary, but that’s irrelevant)
3. env.AppendUnique turns all previous defs without value (that were strings) into tuples with single value, and adds new values also as tuples: (('A', ), ('B', 'C'), ('STM32F4',))
4. CPPScanner expects defs without value to be strings, but any invocation of env.AppendUnique breaks that expectation
5. Scons crashes:

def dictify_CPPDEFINES(env):
    cppdefines = env.get('CPPDEFINES', {})
    if cppdefines is None:
        return {}
    if SCons.Util.is_Sequence(cppdefines):
        result = {}
        for c in cppdefines:
            if SCons.Util.is_Sequence(c):
                result[c[0]] = c[1] # <-- [1] tuple index out of range
            else:
                result[c] = None
        return result

Required information

• Version of SCons 4.3
• Version of Python 3.9
• Which python distribution if applicable (python.org, cygwin, anaconda, macports, brew,etc) brew
• How you installed SCons viaPIO
• What Platform are you on? (Linux/Windows and which version) mac

[mwichmann]

Looks like it's easy enough to patch the hole here, without necessarily tackling the deeper question of why we have keep converting the type of CPPDEFINES.

Do you have a simple example that actually tickles the IndexError

Meanwhile, /me scratches head over:

env = Environment()
env.Append(CPPDEFINES="A")
env.Append(CPPDEFINES="B=C")
env.Append(CPPDEFINES=["STM32F4"])
env.AppendUnique(CPPDEFINES=["STM32F4"])

Showing

env['CPPDEFINES']=['A']
env['CPPDEFINES']=['A', 'B=C']
env['CPPDEFINES']=['A', 'B=C', 'STM32F4']
env['CPPDEFINES']=[('A',), ('B=C',), ('STM32F4',)]

as in - why does Append's speciai-case handling for CPPDEFINES not tuple-ify and AppendUnique's does?

[Inviz]

I think dictify_CPPDEFINES(env) is enough to invoke the issue:

env = Environment()
env.AppendUnique(CPPDEFINES="A")
dictify_CPPDEFINES(env)

I think more proper example of difference would be to env.Append(CPPDEFINES=("B", "C")) (or whatever syntax is to append the tuple, I'm not fluent in python). You'll see that it'll add tuble for ("B", "C"). But for case with no value (e.g. "B") it will keep the string in it. So that means AppendUnique doesn't simplify the values, while Append does (and then other things rely on it)

[mwichmann]

Indeed, it is...

from SCons.Scanner.C import dictify_CPPDEFINES
d = dictify_CPPDEFINES(env)