Compiler/Optimizer Type Inference Bug with Recursive, Nested Types (in v1.12.6)

Internals & Design
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1

The following two examples each produce supposedly impossible results or crash the repl entirely, even though the code is pure Julia. I did not manage to reduce the examples further, at least not by simplifying single lines:

For instance, in the first example, at line 17, changing Vector{Tuple{T,T}} to just Vector{T} fixes the output. In the second example, removing the first field x::UInt from Between so far leads to correct results.

Maybe I am still overlooking something, but as far as I can tell, there is nothing wrong with the code itself.

First example:

mutable struct Bottom{Val_T}
    const val::Val_T
    Bottom{Val_T}() where Val_T = new{Val_T}(Val_T())
end

struct Mid{Val_T}
    val::Val_T
    bottom::Bottom{Val_T}
end

function Mid{Val_T}() where Val_T
    bottom = Bottom{Val_T}()
    Mid(bottom.val, bottom)
end

mutable struct Val{T}
    tuple_TT::Vector{Tuple{T,T}}
    Val{T}() where T = new{T}()
end

struct TopLevel
    mid::Union{Nothing,Mid{Val{TopLevel}}}
end

TopLevel() = TopLevel(Mid{Val{TopLevel}}())
foo(x::Mid) = x

function test()
    x = TopLevel()
    v = TopLevel[x, x]
    y = v[1]

    println(typeof(y) === typeof(x)) # true

    x_mid = getfield(x, :mid)
    println(typeof(x_mid)) # Mid{Val{TopLevel}}
    foo(x_mid)

    y_mid = getfield(y, :mid)
    println(typeof(y_mid)) # TopLevel
    try
        foo(y_mid)
    catch err
        println(err) # MethodError(Main.foo, (TopLevel(Mid{Val{TopLevel}}(Val{TopLevel}(#undef), Bottom{Val{TopLevel}}(Val{TopLevel}(#undef)))),), h*) (*for some UInt h)
    end
end
test()

Second example:

struct Between{Val_T}
    x::UInt
    y::Val_T
    Between{Val_T}() where Val_T = new{Val_T}(UInt(0), Val_T())
end

mutable struct Bottom{Val_T} 
    const val::Val_T
    Bottom{Val_T}() where Val_T = new{Val_T}(Val_T()) 
end

struct Mid{Val_T} 
    val::Val_T
    bottom::Bottom{Val_T}
end

function Mid{Val_T}() where Val_T
    bottom = Bottom{Val_T}()
    Mid(bottom.val, bottom)
end

mutable struct Val{T}
    tuple_TT::Vector{Tuple{T,T}}
    Val{T}() where T = new{T}()
end

struct TopLevel
    mid::Mid{Between{Val{TopLevel}}}
end

TopLevel() = TopLevel(Mid{Between{Val{TopLevel}}}())

function test()
    x = TopLevel()
    v = [x, x]
    y = v[1]

    println("types start equal: $(typeof(y) === typeof(x)) \n") 
    println(y.mid.bottom) # prints ReentrantLock()

    x = TopLevel()
    v = Any[x, x]
    y = v[1]

    println("types start equal: $(typeof(y) === typeof(x)) \n") 
    # println(y.mid) # when uncommented, the repl crashes seemingly randomly sometimes directly, sometimes after rerunning the script several times
end
test()