Increase union stack size

This solves #21191 and similar issues, but there probably is an
underlying problem yet to be solved which makes such a large stack
necessary in the first place.

src/subtype.c

@@ -39,10 +39,12 @@ extern "C" {
 // Union type decision points are discovered while the algorithm works.
 // If a new Union decision is encountered, the `more` flag is set to tell
 // the forall/exists loop to grow the stack.
+// TODO: the stack probably needs to be artifically large because of some
+// deeper problem (see #21191) and could be shrunk once that is fixed
 typedef struct {
     int depth;
     int more;
-    uint32_t stack[10];  // stack of bits represented as a bit vector
+    uint32_t stack[100];  // stack of bits represented as a bit vector
 } jl_unionstate_t;
 
 // Linked list storing the type variable environment. A new jl_varbinding_t

test/inference.jl

@@ -657,8 +657,7 @@ let A = 1:2, z = zip(A, A, A, A, A, A, A, A, A, A, A, A)
 end
 # introduce TypeVars in Unions in invariant position
 let T = Val{Val{Val{Union{Int8,Int16,Int32,Int64,UInt8,UInt16,UInt32,UInt64}}}}
-    #TODO: this test hits an assertion (see #21191)
-    #@test T <: Core.Inference.limit_type_depth(T, 0)
+    @test T <: Core.Inference.limit_type_depth(T, 0)
 end
 
 # issue #20704

test/subtype.jl

@@ -1070,3 +1070,23 @@ end
 @testintersect(Tuple{A20992{R, D, d} where d where D, Int} where R,
                Tuple{C20992{S, n, T, D, d} where d where D where T where n where S, Any},
                Tuple{C20992, Int})
+
+# issue #21191
+let T1 = Val{Val{Val{Union{Int8,Int16,Int32,Int64,UInt8,UInt16}}}},
+    T2 = Val{Val{Val{Union{Int8,Int16,Int32,Int64,UInt8, S}}}} where S
+    @test T1 <: T2
+end
+
+# comment in issue #20103
+let ints = (Int, Int32, UInt, UInt32)
+    const Ints = Union{ints...}
+    vecs = []
+    for i = 2:4, t in ints
+        push!(vecs, NTuple{i, t})
+    end
+    const Vecs = Union{vecs...}
+    T = Type{Tuple{V, I}} where V <: Vecs where I <: Ints
+    @testintersect(T, T, T)
+    test{V <: Vecs, I <: Ints}(a::Type{Tuple{V, I}}) = I
+    test{V <: Vecs, I <: Ints}(a::Type{Tuple{V, I}}) = I
+end