# JET.jl Invalid Type Signature

**URL:** <https://discourse.julialang.org/t/jet-jl-invalid-type-signature/66719>\
**Category:** General Usage\
**Tags:** question, jet\
**Created:** [August 20, 2021, 9:37am UTC](https://discourse.julialang.org/t/jet-jl-invalid-type-signature/66719 "2021-08-20T09:37:42Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![jekyllstein](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jekyllstein/32/4157_2.png) [@jekyllstein](https://discourse.julialang.org/u/jekyllstein)\
**Post date:** [August 20, 2021, 9:37am UTC](https://discourse.julialang.org/t/jet-jl-invalid-type-signature/66719/1 "2021-08-20T09:37:43Z")

</div>

I was trying to use JET.jl to analyze a package and I ran into a type signature error. I have a toy example that reproduces the same issue.

```julia
module Test

ParamType = Union{Tuple{Real, Vararg{Real, N} where N}, Tuple{Real, Real}}
OptParamType = Vector{T} where T <: ParamType

function f(o::OptParamType)
    return true
end

end

```

I have this saved as Test.jl and when I try to use `report_file("Test.jl")` I get the following:

```julia
julia> report_file("Test.jl")
[toplevel-info] virtualized the context of Main (took 0.003 sec)
[toplevel-info] entered into Test.jl
[toplevel-info] exited from Test.jl (took 0.053 sec)
═════ 1 toplevel error found ═════
┌ @ Test.jl:6
│ ArgumentError: invalid type for argument o in method definition for f at Test.jl:6
└─────────────
(included_files = Set(["Test.jl"]), nreported = 1)

```

I’ve seen other messages that suggest I should use `concretization_patterns` to fix this but I have no idea how to use it in this example. The main problem seems to be from having Vararg in the type signature. I’ve tried following some examples from the workshop given by @aviatesk but I’m not experienced enough to solve this so I’d love feedback. Thanks.

---

<div class="post-metadata">

**Author:** ![jakobnissen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jakobnissen/32/13477_2.png) [@jakobnissen](https://discourse.julialang.org/u/jakobnissen)\
**Post date:** [August 22, 2021, 8:07am UTC](https://discourse.julialang.org/t/jet-jl-invalid-type-signature/66719/2 "2021-08-22T08:07:23Z")

</div>

Looks like a bug in JET.jl. Made an issue: [https://github.com/aviatesk/JET.jl/issues/237](https://github.com/aviatesk/JET.jl/issues/237)