Fix type-equality involving Type{Union{}} (#37261)

In particular, make `obviously_unequal(Type{Union{}}, Type{T} where {Union{}<:T<:Union{}})` false. Fixes #37255 (cherry picked from commit 79a9ea0)
JuliaLang · Sep 8, 2020 · 30d5003 · 30d5003
1 parent fa6055c
commit 30d5003
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diff --git a/src/subtype.c b/src/subtype.c
@@ -235,6 +235,10 @@ static int obviously_unequal(jl_value_t *a, jl_value_t *b)
         if (jl_is_datatype(b)) {
             jl_datatype_t *ad = (jl_datatype_t*)a;
             jl_datatype_t *bd = (jl_datatype_t*)b;
+            if (a == (jl_value_t*)jl_typeofbottom_type && bd->name == jl_type_typename)
+                return obviously_unequal(jl_bottom_type, jl_tparam(bd, 0));
+            if (ad->name == jl_type_typename && b == (jl_value_t*)jl_typeofbottom_type)
+                return obviously_unequal(jl_tparam(ad, 0), jl_bottom_type);
             if (ad->name != bd->name)
                 return 1;
             int istuple = (ad->name == jl_tuple_typename);

diff --git a/test/subtype.jl b/test/subtype.jl
@@ -1767,3 +1767,6 @@ end
 
 # issue #37180
 @test !(typeintersect(Tuple{AbstractArray{T}, VecOrMat{T}} where T, Tuple{Array, Any}).body.parameters[1] isa Union)
+
+# issue #37255
+@test Type{Union{}} == Type{T} where {Union{}<:T<:Union{}}