`Vararg` argument as optional argument gives error when there is a keyword argument.

[frankwswang]

MWE:

julia> foo(a, b::Array{Int, 1}...=[0,0];c="") = @show b
foo (generic function with 3 methods)

julia> goo(a,b::Array{Array{Int, 1}, 1}) = begin
       c = "c"
       foo(a, b...;c)
       end
goo (generic function with 3 methods)

julia> goo(1, [[1,2,3]])
ERROR: TypeError: in typeassert, expected Vector{Int64}, got a value of type Tuple{Vector{Int64}}

julia> foo2(a, b::Array{Int, 1}...;c="") = @show b
foo2 (generic function with 1 method)

julia> goo2(a,b::Array{Array{Int, 1}, 1}) = begin
       c = "c"
       foo2(a, b...;c)
       end
goo2 (generic function with 1 method)

julia> goo2(1, [[1,2,3]])
b = ([1, 2, 3],)
([1, 2, 3],)

julia> foo3(a, b::Array{Int, 1}...=[0,0]) = @show b
foo3 (generic function with 2 methods)

julia> goo3(a,b::Array{Array{Int, 1}, 1}) = foo3(a, b...)
goo3 (generic function with 1 method)

julia> goo3(1, [[1,2,3]])
b = ([1, 2, 3],)
([1, 2, 3],)

System info:

julia> versioninfo()
Julia Version 1.6.1
Commit 6aaedecc44 (2021-04-23 05:59 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-1065G7 CPU @ 1.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, icelake-client)
Environment:
  JULIA_NUM_THREADS = 6

Based on the differences among foo, foo2, and foo3, I suspect it might have something to do with the keyword argument syntax but I’m not sure.

I don’t know if this is technically a bug since I haven’t seen the usage of Vararg arguments as optional arguments on the official documentation (I might have missed it so feel free to point out); on the other hand since it’s not forbidden and yet we have this kind of errors. Initial Discourse link is here.

[mcabbott]

Do you need these goo functions? I think this example captures the complaint, but correct me if I have missed something. Here xs is always a tuple of integers:

julia> f(xs::Int... = 99) = xs      # type annotation and default -- works
f (generic function with 2 methods)

julia> f(1, 2, 3)
(1, 2, 3)

julia> f()
(99,)

julia> g(xs... = 99; kw) = xs       # default and keyword -- works
g (generic function with 2 methods)

julia> g(1, 2, 3; kw=0)
(1, 2, 3)

julia> g(kw=0)
(99,)

julia> h(xs::Int... = 99; kw) = xs  # type annotation, default and keyword -- errors
h (generic function with 2 methods)

julia> h(1, 2, 3; kw=0)
ERROR: TypeError: in typeassert, expected Int64, got a value of type Tuple{Int64, Int64, Int64}

julia> h(kw=0)
ERROR: TypeError: in typeassert, expected Int64, got a value of type Tuple{Int64}

julia> h2(xs::Vararg{Int} = 99; kw) = xs  # same as h, different error message
h2 (generic function with 2 methods)

julia> h2(1,2,3; kw=0)
ERROR: MethodError: no method matching var"#h2#8"(::Int64, ::typeof(h2), ::Tuple{Int64, Int64, Int64})

[frankwswang]

Yeah, I think your demo is simpler and more comprehensive. Thanks!