Allow simple concrete union fields for FieldRef

Author: quinnj

Project.toml

@@ -1,13 +1,13 @@
 name = "LibAwsCommon"
 uuid = "c6e421ba-b5f8-4792-a1c4-42948de3ed9d"
-version = "1.3.2"
+version = "1.3.3"
 
 [deps]
 CEnum = "fa961155-64e5-5f13-b03f-caf6b980ea82"
 aws_c_common_jll = "73048d1d-b8c4-5092-a58d-866c5e8d1e50"
 
 [compat]
-Aqua = "0.7"
+Aqua = "0.7,0.8"
 CEnum = "0.5"
 aws_c_common_jll = "=0.12.3"
 julia = "1.6"

src/LibAwsCommon.jl

@@ -72,6 +72,8 @@ function init(allocator=default_aws_allocator())
 end
 
 # utilities for interacting with AWS library APIs
+concrete_or_concreteunion(T) =
+    isconcretetype(T) || (T isa Union && concrete_or_concreteunion(T.a) && concrete_or_concreteunion(T.b))
 
 # like a Ref, but for a field of a struct
 # many AWS APIs take a pointer to an aws struct, so this makes it convenient to to pass
@@ -83,7 +85,7 @@ struct FieldRef{T, S}
     function FieldRef(x::T, field::Symbol) where {T}
         @assert isconcretetype(T) && ismutabletype(T) "only fields of mutable types are supported with FieldRef"
         S = fieldtype(T, field)
-        @assert isconcretetype(S) && !ismutabletype(S) "field type must be concrete and immutable for FieldRef"
+        @assert concrete_or_concreteunion(S) && !ismutabletype(S) "field type must be concrete and immutable for FieldRef"
         return new{T, S}(x, field)
     end
 end