Merge pull request JuliaLang#23602 from JuliaLang/jn/23413

inference: leaftype Type{typeof(Union{})} is ambiguous

base/inference.jl

@@ -403,7 +403,16 @@ const _Type_name = Type.body.name
 isType(@nospecialize t) = isa(t, DataType) && (t::DataType).name === _Type_name
 
 # true if Type is inlineable as constant (is a singleton)
-isconstType(@nospecialize t) = isType(t) && (isleaftype(t.parameters[1]) || t.parameters[1] === Union{})
+function isconstType(@nospecialize t)
+ isType(t) || return false
+ p1 = t.parameters[1]
+ # typeof(Bottom) is special since even though it is as leaftype,
+ # at runtime, it might be Type{Union{}} instead, so don't attempt inference of it
+ p1 === typeof(Union{}) && return false
+ p1 === Union{} && return true
+ isleaftype(p1) && return true
+ return false
+end
 
 iskindtype(@nospecialize t) = (t === DataType || t === UnionAll || t === Union || t === typeof(Bottom))
 
@@ -1147,13 +1156,9 @@ function getfield_tfunc(@nospecialize(s00), @nospecialize(name))
  rewrap(getfield_tfunc(s.b, name),s00))
  elseif isa(s, Conditional)
  return Bottom # Bool has no fields
- elseif isa(s, Const) || isType(s)
+ elseif isa(s, Const) || isconstType(s)
  if !isa(s, Const)
- p1 = s.parameters[1]
- if !isleaftype(p1)
- return Any
- end
- sv = p1
+ sv = s.parameters[1]
  else
  sv = s.val
  end
@@ -1189,7 +1194,7 @@ function getfield_tfunc(@nospecialize(s00), @nospecialize(name))
  end
  s = typeof(sv)
  end
- if !isa(s,DataType) || s.abstract
+ if isType(s) || !isa(s, DataType) || s.abstract
  return Any
  end
  if s <: Tuple && name ⊑ Symbol

test/inference.jl

@@ -1198,3 +1198,6 @@ g23024(TT::Tuple{DataType}) = f23024(TT[1], v23024)
 @test Base.return_types(f23024, (DataType, Any)) == Any[Int]
 @test Base.return_types(g23024, (Tuple{DataType},)) == Any[Int]
 @test g23024((UInt8,)) === 2
+
+@test !Core.Inference.isconstType(Type{typeof(Union{})}) # could be Core.TypeofBottom or Type{Union{}} at runtime
+@test Base.return_types(supertype, (Type{typeof(Union{})},)) == Any[Any]