Inference suboptimality when using nested generators

[jonathan-laurent]

The following code does not infer using Julia 1.7.3:

f(n) = (i^2 for i in 1:n)
g(n) = sum(x^2 for x in f(n))
@code_warntype g(3)

Output:

MethodInstance for g(::Int64)
  from g(n) in Main at /home/jonathan/AlphaZero.jl/redesign/private/inference.jl:2
Arguments
  #self#::Core.Const(g)
  n::Int64
Locals
  #61::var"#61#62"
Body::Any
1 ─      (#61 = %new(Main.:(var"#61#62")))
│   %2 = #61::Core.Const(var"#61#62"())
│   %3 = Main.f(n)::Core.PartialStruct(Base.Generator{UnitRange{Int64}, var"#59#60"}, Any[Core.Const(var"#59#60"()), Core.PartialStruct(UnitRange{Int64}, Any[Core.Const(1), Int64])])
│   %4 = Base.Generator(%2, %3)::Core.PartialStruct(Base.Generator{Base.Generator{UnitRange{Int64}, var"#59#60"}, var"#61#62"}, Any[Core.Const(var"#61#62"()), Core.PartialStruct(Base.Generator{UnitRange{Int64}, var"#59#60"}, Any[Core.Const(var"#59#60"()), Core.PartialStruct(UnitRange{Int64}, Any[Core.Const(1), Int64])])])
│   %5 = Main.sum(%4)::Any
└──      return %5

This issue is crossposted from Discourse.