Exclude certain combinations from powerset

[wmmc88]

Is it possible to use cargo-hack to iterate over a feature powerset, but explicitly still skip certain combinations? For example, if my crate has the independent features: a, b, c

My understanding is --feature-powerset will run with the following combinations:

• a
• b
• c
• a, b
• a, c
• b, c
• a, b, c
• no features

Is there a way to tell cargo-hack to ignore a certain combinations here? For example, lets say I know a + c has some problems right now, can i tell cargo-hack to exclude that specific combination?

[taiki-e]

There is --mutually-exclusive-features option.

cargo-hack/tests/long-help.txt

Lines 111 to 117 in 79eb9dc

	--mutually-exclusive-features <FEATURES>...
	Space or comma separated list of features to not use together.
	To specify multiple groups, use this option multiple times:
	`--mutually-exclusive-features a,b --mutually-exclusive-features c,d`
	This flag can only be used together with --feature-powerset flag.

[wmmc88]

I'm aware of mutually exclusive option but I don't think it does what I want here. Wouldn't adding a, c to mutually exclusive list also exclude a, b, c?

[taiki-e]

Oh, there is indeed no ability to exclude “specific combination”. I would accept PR to support this.

[hsqStephenZhang]

hi, i think its reasonable to let user provide some formulas like "¬(a & b)" to tell the checker that feature a and b cannot exists at the same time(could be easily done by adding a compile_error! in the source code)

i have noticed that we have options like "at-least-one-of", "mutually-exclusive-features", which is another way of describing the logic relationships, but could not express other kind of logics. furthermore, these options are more scattered, being not so obvious to some users.

Maybe we could provide --formula, which would overwrite options that is a subset of it to make it more expressive.

i'd like to make a draft if it sounds plausible.