UnionAll type `where T<:...` conflict with type `T` leads to syntax error "invalid type parameter name 'SSAValue'"

[quachpas]

When an UnionAll type with a nonunique name is specified, a syntax error "invalid type parameter name "SSAValue"" is raised.

MWE (error): Foo{T<:Integer, U<:AbstractArray{T} where T<:Integer}

julia> struct Foo{T<:Integer, U<:AbstractArray{T} where T<:Integer}
             a::T
             b::U
         end
ERROR: syntax: invalid type parameter name "SSAValue(404)" around REPL[21]:2
Stacktrace:
 [1] top-level scope
   @ REPL[21]:1
 [2] top-level scope
   @ ~/.julia/juliaup/julia-1.10.2+0.x64.linux.gnu/share/julia/stdlib/v1.10/REPL/src/REPL.jl:1428

When it is a simple type, the nested type T is identified as the first one T<:Integer.

Without UnionAll (no error): Bar{T<:Integer, U<:AbstractArray{T}}

julia> struct Bar{T<:Integer, U<:AbstractArray{T}}
             a::T
             b::U
         end

julia> Bar(1, [1])
Bar{Int64, Vector{Int64}}(1, [1])


julia> Bar(1, [Int32(1])
ERROR: MethodError: no method matching Bar(::Int64, ::Vector{Int32})

Closest candidates are:
  Bar(::T, ::U) where {T<:Integer, U<:(AbstractArray{T})}
   @ Main REPL[45]:2

Stacktrace:
 [1] top-level scope
   @ REPL[64]:1
 [2] top-level scope
   @ ~/.julia/juliaup/julia-1.10.2+0.x64.linux.gnu/share/julia/stdlib/v1.10/REPL/src/REPL.jl:1428

With a simple UnionAll type, everything works as expected

Without conflicting name (no error): FooBar{U<:AbstractArray{T} where T<:Integer}

struct FooBar{U<:AbstractArray{T} where T<:Integer}
                      b::U
                  end

julia> FooBar([1])
FooBar{Vector{Int64}}([1])

julia> FooBar([Int32(1)])
FooBar{Vector{Int32}}(Int32[1])

Below are existing errors for different, but similar situations

function static parameter name not unique: struct BarFoo{T<:Integer, T<:AbstractFloat}

julia> struct BarFoo{T<:Integer, T<:AbstractFloat}
             a::T
         end
ERROR: syntax: function static parameter name not unique: "T" around REPL[22]:2
Stacktrace:
 [1] top-level scope
   @ REPL[22]:1
 [2] top-level scope
   @ ~/.julia/juliaup/julia-1.10.2+0.x64.linux.gnu/share/julia/stdlib/v1.10/REPL/src/REPL.jl:1428

function argument and static parameter name not distinct: foo(A::A) where A<:Integer = A()

julia> foo(A::A) where A<:Integer = A()
ERROR: syntax: function argument and static parameter name not distinct: "A" around REPL[13]:1
Stacktrace:
 [1] top-level scope
   @ REPL[13]:1
 [2] top-level scope
   @ ~/.julia/juliaup/julia-1.10.2+0.x64.linux.gnu/share/julia/stdlib/v1.10/REPL/src/REPL.jl:1428

versioninfo

julia> versioninfo()
Julia Version 1.10.2
Commit bd47eca2c8a (2024-03-01 10:14 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 8 × 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, tigerlake)
Threads: 1 default, 0 interactive, 1 GC (on 8 virtual cores)

Thanks!

[Keno]

``

julia> struct Foo{T<:Integer, U<:AbstractArray{T} where T<:Integer}
             a::T
             b::U
         end
ERROR: syntax: invalid type parameter name "SSAValue(404)" around REPL[21]:2
Stacktrace:
 [1] top-level scope
   @ REPL[21]:1
 [2] top-level scope
   @ ~/.julia/juliaup/julia-1.10.2+0.x64.linux.gnu/share/julia/stdlib/v1.10/REPL/src/REPL.jl:1428

Looks like a bug where lowering doesn't recognize that where introduces local bindings and tries to use the tparam instead.

All other errors are intentional.

[quachpas]

All other errors are intentional.

Yes! Sorry for the confusion, the other errors were added for context. I was not sure whether this particular situation should raise an error or not?
Given that Bar{T<:Integer, U<:AbstractArray{T}} works as expected, then the first situation looks ambiguous to me, e.g. should Foo{T<:Integer, U<:AbstractArray{T} where T<:AbstractFloat} work?

[Keno]

should Foo{T<:Integer, U<:AbstractArray{T} where T<:AbstractFloat} work?

Yes, where should shadow the outer definition of T.

[mlechu]

Appears to have been fixed by #57317