Skipping axes with CannotDecide makes boolean operations act nothing like boolean operations.

[t184256]

>>> fmf.context.Context(package='pkg-1').matches('package <= pkg-2')
True
>>> fmf.context.Context(distro='fedora-33').matches('distro <= centos-7.7')
...
fmf.context.CannotDecide
>>> fmf.context.Context(package='pkg-1', distro='fedora-33').matches('package < pkg-2 and distro <= centos-7.7')
True

This is documented:

Expression skipping When a dimension or outcome of the operation is not defined, the expression is skipped over.

But it's absolutely counterintuitive.

Consequential weird things:

• distro < rhel-8 and distro < fedora-33: True for fedora-32, False for fedora-99
• distro < rhel-8 or distro < fedora-33: True for fedora-32, False for fedora-99

Counter-proposal:

CannotDecide and True = True and CannotDecide = CannotDecide CannotDecide and False = False and CannotDecide = False CannotDecide or True = True or CannotDecide = True CannotDecide or False = False or CannotDecide = CannotDecide

[t184256]

Rationale for the counterproposal:

• annihilation rules are strong, short-circuiting boolean evaluators wouldn't even look at what goes after True or / False and
• or True and and False should do the same to maintain commutativity
• X and True is X and X or False is X in boolean logic
• True and X is X and False or X is X holds true even outside of boolean logic (e.g. with Python's short-circuiting evaluator)
• CannotDecide taints every other operation with CannotDecide to err on the safe side (and to have a clear safe side)

[jscotka]

HI, I can imagine, also some command line option what will do some tweaking of some default values.

I can imagine, some fallback syntax, eg. when you will have e.g. filter: X and Y or Z, I can imagine some syntax like

• filter: X[True] and Y[False] or dist <= centos-8[False], what will use this default value if variable is not defined.
• filter: X:=True Y:=False dist:=centos-9 X and Y or dist <= centos-8 or this will assign some default value to variables if they are not defined, and then logic formulas will be same.

What will add very powerful tooling. and will be nice

[lukaszachy]

@jscotka Thanks for the idea, lets discuss it there and leave this issue just for CannotDecide problem