UndefVarError with tuple destructuring

[mwarusz]

julia> function f((x, y))
       let
        T = Int
        x::T = 3
        y::T = 4
       end
       end
f (generic function with 1 method)

julia> f((1, 2))
ERROR: UndefVarError: T not defined

I am using Julia version 1.5.2. This works correctly if the function signature is f(x, y).

[vchuravy]

The let block is not necessary it seems mostly related to tuple destructuring.

julia> function f((x, y))
        T = Int
        x::T = 3
        y::T = 4
       end

[simeonschaub]

Doesn't have anything to do with tuple destructuring either 😄 :

julia> let x = 1
           T = Int
           x::T = 2
       end
ERROR: UndefVarError: T not defined
Stacktrace:
 [1] top-level scope
   @ REPL[13]:1

I don't think this can actually work in general, because typeasserts on the lhs apply to the binding x anywhere in the current scope, which is not possible if T is only defined somewhere later in this scope, so this might just need a better error message.

[vchuravy]

julia> function f(x, y)
         let T = Int
           x::T = 3
           y::T = 4
         end
       end
f (generic function with 1 method)

does actually work.

But you are right... All this is an effect of typeassert. I think this should lead to a error message during lowering.

[simeonschaub]

Yes, that's because the inner x and ys are now defined in a different scope, so the typeasserts are only for the inner let block, not the entire function block.

[adienes]

looks like a duplicate of #28268