errors and warnings / types / W2061

W2061 warning

a and nil or b (or false in the middle) is always b: the falsy middle value makes the or take over (any mode)

area: types (x2xxx)
fails the build: with --deny-warnings

a and nil or b (or false in the middle) is always b: when a is truthy, a and nil is nil, so the or takes over and gives b anyway. The idiom can't give a falsy value. Write not a and b or nil when b is never falsy, or an if.

Example

× failswowlua

local function gapFor(subtitle: string?): number?    return subtitle and nil or 8endprint(gapFor("x"))

✓ compileswowlua

local function gapFor(subtitle: string?): number?    return not subtitle and 8 or nilendprint(gapFor("x"))

The compiler reports it like this:

warning[W2061]: `a and nil or b` is always `b`: the `nil` makes the `or` take over (write `not a and b or nil`, or an `if`)
  ┌─ src/main.wowlua:2:12
  │
2 │     return subtitle and nil or 8
  │            ^^^^^^^^^^^^^^^^ here

Offline

terminal

$ wowlua explain W2061
W2061 (warning): a and nil or b (or false in the middle) is always b: the falsy middle value makes the or take over (any mode)

source on GitHub ↗