From 810d183070951ad841dbef18f61b99c290a85ec4 Mon Sep 17 00:00:00 2001
From: Tim Holy <tim.holy@gmail.com>
Date: Thu, 25 Feb 2021 11:07:56 -0600
Subject: [PATCH] equiv_typedef: don't reject equivalence just for gensyms
 (#39778)

This fixes the following:

```
julia> struct Symmetric{T,S<:AbstractMatrix{<:T}} <: AbstractMatrix{T}
           data::S
           uplo::Char
       end

julia> struct Symmetric{T,S<:AbstractMatrix{<:T}} <: AbstractMatrix{T}
           data::S
           uplo::Char
       end
ERROR: invalid redefinition of constant Symmetric
```

`Core._equiv_typedef` returns false which ends up triggering the error.
---
 src/builtins.c |  2 +-
 test/core.jl   | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/builtins.c b/src/builtins.c
index 10e2092a0be78..c85ea1750348e 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -1395,7 +1395,7 @@ static int equiv_type(jl_value_t *ta, jl_value_t *tb)
     while (jl_is_unionall(a)) {
         jl_unionall_t *ua = (jl_unionall_t*)a;
         jl_unionall_t *ub = (jl_unionall_t*)b;
-        if (!jl_egal(ua->var->lb, ub->var->lb) || !jl_egal(ua->var->ub, ub->var->ub) ||
+        if (!jl_types_egal(ua->var->lb, ub->var->lb) || !jl_types_egal(ua->var->ub, ub->var->ub) ||
             ua->var->name != ub->var->name)
             goto no;
         a = jl_instantiate_unionall(ua, (jl_value_t*)ub->var);
diff --git a/test/core.jl b/test/core.jl
index a159aeccf1d55..c360dc6ba5b13 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -7289,12 +7289,28 @@ end
 
 # issue #36104
 module M36104
+using Test
 struct T36104
     v::Vector{M36104.T36104}
 end
 struct T36104   # check that redefining it works, issue #21816
     v::Vector{T36104}
 end
+# with a gensymmed unionall
+struct Symmetric{T,S<:AbstractMatrix{<:T}} <: AbstractMatrix{T}
+    data::S
+    uplo::Char
+end
+struct Symmetric{T,S<:AbstractMatrix{<:T}} <: AbstractMatrix{T}
+    data::S
+    uplo::Char
+end
+@test_throws ErrorException begin
+    struct Symmetric{T,S<:AbstractMatrix{T}} <: AbstractMatrix{T}
+        data::S
+        uplo::Char
+    end
+end
 end
 @test fieldtypes(M36104.T36104) == (Vector{M36104.T36104},)
 @test_throws ErrorException("expected") @eval(struct X36104; x::error("expected"); end)