Error: undefined constant U

[mamantoha]

Hi team.

I didn't get how to reproduce this error.
But after #10467 my code start fail.

This is the end to the outputt.

In /snap/crystal/874/share/crystal/src/array.cr:208:5

 208 | equals?(other) { |x, y| x == y }
       ^------
Error: instantiating 'equals?((Array(PG::BoolArray) | Array(PG::CharArray) | Array(PG::Float32Array) | Array(PG::Float64Array) | Array(PG::Int16Array) | Array(PG::Int32Array) | Array(PG::Int64Array) | Array(PG::NumericArray) | Array(PG::StringArray) | Array(PG::TimeArray)))'


In /snap/crystal/874/share/crystal/src/indexable.cr:413:33

 413 | def equals?(other : Indexable(U), & : T, U ->) : Bool forall U
                                     ^
Error: undefined constant U

Looks like a typo.

Let me know if I need to provide more info.

/cc @straight-shoota

[straight-shoota]

There is no obvious error with that def. I have no idea how U can be undefined since it's explicitly declared as a free variable.

Stdlib specs are passing.

crystal/spec/std/array_spec.cr

Lines 689 to 698 in 685da9d

	it "does equals? with custom block" do
	a = [1, 3, 2]
	b = [3, 9, 4]
	c = [5, 7, 3]
	d = [1, 3, 2, 4]
	f = ->(x : Int32, y : Int32) { (x % 2) == (y % 2) }
	a.equals?(b, &f).should be_true
	a.equals?(c, &f).should be_false
	a.equals?(d, &f).should be_false
	end

We need some code to reproduce the error.

[mamantoha]

I will try to extract the code to reproduce this issue.

[HertzDevil]

The original error seems to come from here: https://github.com/mamantoha/clear/runs/3681933489

Reduced:

alias Foo = Int32 | Array(Foo)
alias Bar = String | Array(Bar)

x = 1.as(Foo | Bar)
x == x # Error: undefined constant U

For now I suggest not replacing parameter restrictions like Indexable with Indexable(T) forall T until #8973 is settled. (The addition of free variables there is essentially the opposite of #10510, by the way.)

[rubyFeedback]

The magic constant U has been discovered!

[caspiano]

Looks like this is also showing up for Enumerable#in_groups_of

https://github.com/caspiano/crystal-redis/runs/3864309457?check_suite_focus=true#step:10:12