Julia: inconsistent error for `let` bound variables conflicting with static parameters

[thautwarm]

EDIT:

julia> function f(x::T) where {C1, C2, T}
           let C1 = 1,
               C2 = 2
               (C1, C2, T)
           end
       end
f (generic function with 1 method)

julia> f(1)
ERROR: UndefVarError: C1 not defined

[timholy]

Am I understanding correctly that you're asking for a new feature in which static parameters can be supplied with default values? What is the use case for this? In general the static parameters should be determined by the input types.

[thautwarm]

@timholy No, it's okay to leave the non-dispatched static parameters undefined, i.e, I think this is expected:

julia> function f(x::T) where {C1, C2, T}
           C1
       end
f (generic function with 1 method)

julia> f(1)
ERROR: UndefVarError: C1 not defined

However, in my first post I used a let binding to enter a new scope, and bind C1 = 1.

Is this explanation clear to you?

[timholy]

Nope. If this is a feature request, you need to clarify why you want this. If you think it's a bug (it's not), please ask questions on discourse.

[timholy]

Oh wait, now I understand (sorry!): this is a bug report. Compare the following:

julia> function g(x::T) where {C1, C2, T}
           let C1 = 1, C2 = 2
               return (C1, C2, T)
           end
       end
g (generic function with 1 method)

julia> function h(x::T) where {C, T}
           let C = 1
               return (C, T)
           end
       end
h (generic function with 1 method)

julia> h(nothing)
(1, Nothing)

julia> g(nothing)
ERROR: UndefVarError: C1 not defined
Stacktrace:
 [1] g(::Nothing) at ./REPL[1]:3
 [2] top-level scope at REPL[4]:1

julia> @code_lowered h(nothing)
CodeInfo(
1 ─      C = 1
│   %2 = Core.tuple(C, $(Expr(:static_parameter, 2)))
└──      return %2
)

julia> @code_lowered g(nothing)
CodeInfo(
1 ─      C1 = 1
│        C2 = 2
│   %3 = Core.tuple($(Expr(:static_parameter, 1)), C2, $(Expr(:static_parameter, 3)))
└──      return %3
)

It's of course not how you should write Julia code, but the inconsistency is a bug.