Array(T)#* of recursive type alias

[lbguilherme]

When updating an old project to the current Crystal release I found a case that used to work but now fails to build and looks like a compiler bug. Here is a reduced version:

alias Type = Array(Type) | String

arr = ["aa", ["23"]] of Type

p arr # this works
p arr * 2 # this doesn't compile

Here is the compiler output:

In test.cr:6:7

 6 | p arr * 2
           ^
Error: instantiating 'Array(Type)#*(Int32)'


In /usr/share/crystal/src/array.cr:337:23

 337 | return Array(T).new(times, first)
                       ^--
Error: instantiating 'Array(Type).class#new(Int32, (Array(String) | Array(Type) | String))'


In /usr/share/crystal/src/array.cr:116:7

 116 | @buffer = Pointer(T).malloc(size, value)
       ^------
Error: instance variable '@buffer' of Array(Type) must be Pointer(Array(String) | Array(Type) | String), not Pointer(Array(String) | Array(Type) | String)

In particular, notice that the last line says Pointer(Array(String) | Array(Type) | String) is not the same as Pointer(Array(String) | Array(Type) | String). But they look pretty much the same to me. Not sure what is going on.

This used to work on Crystal 0.30.1 (https://play.crystal-lang.org/#/r/88y1) but broke on Crystal 0.31.0 (https://play.crystal-lang.org/#/r/88y0)

[lbguilherme]

arr.uniq also fails to compile for a recursive type.

May be worth to mention: #5155

[Sija]

Possibly related to #8087 and/or #8048.

[asterite]

The first snippet shouldn't compile at all because an Array(String) is inserted into Array(Type). This is a bug.

I hope someone removes recursive aliases in the future...

[HertzDevil]

The original snippet no longer compiles due to #10224.

[lbguilherme]

The original snippet now doesn't compile with a correct error message. And this example correctly compiles:

alias Type = Array(Type) | String

arr = ["aa", ["23"] of Type] of Type

p arr
p arr * 2