Cop idea: Style/BitPredicates

[zverok]

Is your feature request related to a problem? Please describe.

Ruby 2.5 (!) introduced Integer#anybits?/#allbits?/#nobits? predicates. Accordingly, it would be cool if Rubocop suggested those corrections:

# 1. anybits?
# bad
(variable & MY_FLAGS).positive?
# good
variable.anybits?(MY_FLAGS)

# 2. allbits?
# bad
(variable & MY_FLAGS) == MY_FLAGS
# good
variable.allbits?(MY_FLAGS)

# 3. nobits?
# bad
(variable & MY_FLAGS).zero?
# good
variable.nobits?(MY_FLAGS)

I’ve seen a lot of codebases that use the bit-math version, and in many cases, predicates version seems to be clearer. It also has an educational value: I constantly see people writing bit-math to check flags seven years after methods introduction (because they simply don’t remember methods exist).

Haven’t yet time enough to work on the cop myself (well, I happen to have a draft branch, and I feel guilty for never finishing it, maybe I’ll do... but it is what it is) 😢

[vlad-pisanov]

One can also access individual bits via [], perhaps it could be part of such a cop as well.

Bit extraction:

# bad
(x >> bit) & 1

# good
x[bit]

Bit checking:

# bad
x & (1 << bit) > 0

# good
x[bit] == 1

# bad
x & (1 << bit) == 0

# good
x[bit] == 0

Bit checking against constant powers of 2:

# bad
(x & 8).positive?
(x & 0b01000).positive?
(x & (1 << 3)).positive?
(x & 8) == 8

# good
x[3] == 1