From 2901f0e353c5e5fdb341caa9abce92b042248627 Mon Sep 17 00:00:00 2001
From: N5N3 <2642243996@qq.com>
Date: Thu, 29 Dec 2022 06:04:09 +0800
Subject: [PATCH] Avoid stack-overflow in #46736

When we perform re-`intersection_unionall`, the `Union` bounds might be generated from `simple_join  and thus not identical to the src `Union`.
This commit adds a fast-path to skip the following `intersect_all.
---
 src/subtype.c   | 3 +++
 test/subtype.jl | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/src/subtype.c b/src/subtype.c
index 9356f0d943e9b..c4207840ae519 100644
--- a/src/subtype.c
+++ b/src/subtype.c
@@ -2150,6 +2150,9 @@ 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 (jl_egal(x, y))
+        return x;
 
     jl_saved_unionstate_t oldRunions; push_unionstate(&oldRunions, &e->Runions);
     int savedepth = e->invdepth, Rsavedepth = e->Rinvdepth;
diff --git a/test/subtype.jl b/test/subtype.jl
index 9239c66decff1..d5f07f722f5ca 100644
--- a/test/subtype.jl
+++ b/test/subtype.jl
@@ -2296,6 +2296,14 @@ let S = Tuple{Type{T},Array{Union{T,Missing},N}} where {T,N},
     @test_broken I <: T
 end
 
+#issue 46736
+let S = Tuple{Val{T}, T} where {S1,T<:Val{Union{Nothing,S1}}},
+    T = Tuple{Val{Val{Union{Nothing, S2}}}, Any} where S2
+    @testintersect(S, T, !Union{})
+    # not ideal (`S1` should be unbounded)
+    @test_broken testintersect(S, T) == Tuple{Val{Val{Union{Nothing, S1}}}, Val{Union{Nothing, S1}}} where S1<:(Union{Nothing, S2} where S2)
+end
+
 @testset "known subtype/intersect issue" begin
     #issue 45874
     # Causes a hang due to jl_critical_error calling back into malloc...