typeintersect: more fastpath to skip intersect under circular env (#56304)

fix #56040

(cherry picked from commit 53ffe56)

Author: N5N3

src/subtype.c

@@ -2392,8 +2392,10 @@ static jl_value_t *intersect_aside(jl_value_t *x, jl_value_t *y, jl_stenv_t *e,
         return y;
     if (y == (jl_value_t*)jl_any_type && !jl_is_typevar(x))
         return x;
-    // band-aid for #46736
-    if (obviously_egal(x, y))
+    // band-aid for #46736 #56040
+    if (obviously_in_union(x, y))
+        return y;
+    if (obviously_in_union(y, x))
         return x;
 
     jl_saved_unionstate_t oldRunions; push_unionstate(&oldRunions, &e->Runions);
@@ -2407,6 +2409,9 @@ static jl_value_t *intersect_aside(jl_value_t *x, jl_value_t *y, jl_stenv_t *e,
 
 static jl_value_t *intersect_union(jl_value_t *x, jl_uniontype_t *u, jl_stenv_t *e, int8_t R, int param)
 {
+    // band-aid for #56040
+    if (!jl_is_uniontype(x) && obviously_in_union((jl_value_t *)u, x))
+        return x;
     if (param == 2 || (!jl_has_free_typevars(x) && !jl_has_free_typevars((jl_value_t*)u))) {
         jl_value_t *a=NULL, *b=NULL;
         JL_GC_PUSH2(&a, &b);

test/subtype.jl

@@ -2641,3 +2641,12 @@ let S = Tuple{Val, Val{T}} where {T}, R = Tuple{Val{Val{T}}, Val{T}} where {T},
     @testintersect(Tuple{Val{A}, A} where {B, A<:Union{Val{B}, NamedTuple{(:a),B}}}, S{NTuple{2,Int}}, R{NTuple{2,Int}})
     @testintersect(Tuple{Val{A}, A} where {B, A<:Union{Val{B}, NamedTuple{B,Tuple{Int,Int}}}}, S{(:a,:a)}, R{(:a,:a)})
 end
+
+#issue 56040
+let S = Dict{V,V} where {V},
+    T = Dict{Ref{Union{Set{A2}, Set{A3}, A3}}, Ref{Union{Set{A3}, Set{A2}, Set{A1}, Set{A4}, A4}}} where {A1, A2<:Set{A1}, A3<:Union{Set{A1}, Set{A2}}, A4<:Union{Set{A2}, Set{A1}, Set{A3}}},
+    A = Dict{Ref{Set{Union{}}}, Ref{Set{Union{}}}}
+    @testintersect(S, T, !Union{})
+    @test A <: typeintersect(S, T)
+    @test A <: typeintersect(T, S)
+end