From 020efa3aeee0170c532de2bdae84ef3b555fd354 Mon Sep 17 00:00:00 2001
From: Matt Fishman <mtfishman@users.noreply.github.com>
Date: Fri, 11 Oct 2024 20:18:39 -0400
Subject: [PATCH] [NDTensors] Fix type promotion of EmptyNumber in Julia 1.11
 (#1541)

* [NDTensors] Fix type promotion of EmptyNumber in Julia 1.11

* [NDTensors] Bump to v0.3.44
---
 NDTensors/Project.toml             |  2 +-
 NDTensors/src/empty/EmptyTensor.jl |  2 --
 NDTensors/src/emptynumber.jl       |  8 ++++++++
 NDTensors/test/test_emptynumber.jl | 13 ++++++++++---
 4 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/NDTensors/Project.toml b/NDTensors/Project.toml
index 65771b0c5a..5fa45ba4d6 100644
--- a/NDTensors/Project.toml
+++ b/NDTensors/Project.toml
@@ -1,7 +1,7 @@
 name = "NDTensors"
 uuid = "23ae76d9-e61a-49c4-8f12-3f1a16adf9cf"
 authors = ["Matthew Fishman <mfishman@flatironinstitute.org>"]
-version = "0.3.43"
+version = "0.3.44"
 
 [deps]
 Accessors = "7d9f7c33-5ae7-4f3b-8dc6-eff91059b697"
diff --git a/NDTensors/src/empty/EmptyTensor.jl b/NDTensors/src/empty/EmptyTensor.jl
index 3fcbf4ed63..f5e04e0652 100644
--- a/NDTensors/src/empty/EmptyTensor.jl
+++ b/NDTensors/src/empty/EmptyTensor.jl
@@ -152,8 +152,6 @@ end
 
 setindex!!(T::EmptyTensor, x, I...) = setindex(T, x, I...)
 
-promote_rule(::Type{EmptyNumber}, ::Type{T}) where {T<:Number} = T
-
 function promote_rule(
   ::Type{T1}, ::Type{T2}
 ) where {T1<:EmptyStorage{EmptyNumber},T2<:TensorStorage}
diff --git a/NDTensors/src/emptynumber.jl b/NDTensors/src/emptynumber.jl
index d84abb52ca..1d9799b740 100644
--- a/NDTensors/src/emptynumber.jl
+++ b/NDTensors/src/emptynumber.jl
@@ -18,6 +18,14 @@ convert(::Type{T}, x::EmptyNumber) where {T<:Number} = T(zero(T))
 # This helps with defining `norm` of `EmptyStorage{EmptyNumber}`.
 AbstractFloat(::EmptyNumber) = zero(AbstractFloat)
 
+# Extra definitions fix ambiguity errors.
+Base.promote_rule(::Type{EmptyNumber}, T::Type{<:Number}) = T
+Base.promote_rule(T::Type{<:Number}, ::Type{EmptyNumber}) = T
+Base.promote_rule(::Type{EmptyNumber}, ::Type{Bool}) = Bool
+Base.promote_rule(::Type{Bool}, ::Type{EmptyNumber}) = Bool
+Base.promote_rule(::Type{EmptyNumber}, T::Type{Complex{R}}) where {R<:Real} = T
+Base.promote_rule(T::Type{Complex{R}}, ::Type{EmptyNumber}) where {R<:Real} = T
+
 # Basic arithmetic
 (::EmptyNumber + ::EmptyNumber) = EmptyNumber()
 (::EmptyNumber - ::EmptyNumber) = EmptyNumber()
diff --git a/NDTensors/test/test_emptynumber.jl b/NDTensors/test/test_emptynumber.jl
index dc8357a115..73d82117f5 100644
--- a/NDTensors/test/test_emptynumber.jl
+++ b/NDTensors/test/test_emptynumber.jl
@@ -1,14 +1,21 @@
 @eval module $(gensym())
-using NDTensors
+using LinearAlgebra: norm
+using NDTensors: EmptyNumber
 using Test: @testset, @test, @test_throws
 
-const 𝟎 = NDTensors.EmptyNumber()
+const 𝟎 = EmptyNumber()
 
 @testset "NDTensors.EmptyNumber" begin
   x = 2.3
 
   @test complex(𝟎) == 𝟎
-  @test complex(NDTensors.EmptyNumber) == Complex{NDTensors.EmptyNumber}
+  @test complex(EmptyNumber) == Complex{EmptyNumber}
+
+  # Promotion
+  for T in (Bool, Float32, Float64, Complex{Float32}, Complex{Float64})
+    @test promote_type(EmptyNumber, T) === T
+    @test promote_type(T, EmptyNumber) === T
+  end
 
   # Basic arithmetic
   @test 𝟎 + 𝟎 == 𝟎