Fix promotion between UnspecifiedZero and Bool (#7)

Project.toml

@@ -1,7 +1,7 @@
 name = "UnspecifiedTypes"
 uuid = "42b3faec-625b-4613-8ddc-352bf9672b8d"
 authors = ["ITensor developers <[email protected]> and contributors"]
-version = "0.1.2"
+version = "0.1.3"
 
 [compat]
 julia = "1.10"

src/unspecifiedzero.jl

@@ -35,3 +35,9 @@ Base.:-(::UnspecifiedZero) = UnspecifiedZero()
 Base.promote_rule(::Type{<:UnspecifiedZero}, t::Type) = t
 Base.promote_rule(::Type{<:UnspecifiedZero}, ::Type{<:UnspecifiedZero}) = UnspecifiedZero
 Base.promote_type(::Type{<:Complex{<:UnspecifiedZero}}, t::Type) = complex(t)
+
+# Avoid circular definition in `Base.promote_type`, since
+# Base defines `promote_rule(::Type{Bool}, ::Type{T}) where {T<:Number} = T`.
+# I.e. normally numbers take precedence over `Bool`, but that
+# isn't the case for `UnspecifiedZero`.
+Base.promote_rule(::Type{Bool}, ::Type{<:UnspecifiedZero}) = Union{}

test/test_basics.jl

@@ -13,4 +13,9 @@ using Test: @testset, @test
     @test x isa UnspecifiedZero
     @test x === UnspecifiedZero()
   end
+
+  # Normally, any number type takes precedence over
+  # `Bool`, check this isn't the case with `UnspecifiedZero`.
+  @test promote_type(UnspecifiedZero, Bool) === Bool
+  @test promote_type(Bool, UnspecifiedZero) === Bool
 end