From b38fde1ad42c977878d4f481c962b108a3ae20ab Mon Sep 17 00:00:00 2001
From: Neven Sajko <s@purelymail.com>
Date: Fri, 25 Oct 2024 09:26:36 +0200
Subject: [PATCH] support `isless` for zero-dimensional `AbstractArray`s
 (#55772)

Fixes #55771
---
 NEWS.md               | 1 +
 base/abstractarray.jl | 9 +++++++++
 test/arrayops.jl      | 8 ++++++++
 3 files changed, 18 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index cf04fbf577248..658dcc7aa320e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -117,6 +117,7 @@ New library features
 * `RegexMatch` objects can now be used to construct `NamedTuple`s and `Dict`s ([#50988])
 * `Lockable` is now exported ([#54595])
 * New `ltruncate`, `rtruncate` and `ctruncate` functions for truncating strings to text width, accounting for char widths ([#55351])
+* `isless` (and thus `cmp`, sorting, etc.) is now supported for zero-dimensional `AbstractArray`s ([#55772])
 
 Standard library changes
 ------------------------
diff --git a/base/abstractarray.jl b/base/abstractarray.jl
index e877a87c2cdd1..cbbae8e852b2e 100644
--- a/base/abstractarray.jl
+++ b/base/abstractarray.jl
@@ -3044,6 +3044,15 @@ function cmp(A::AbstractVector, B::AbstractVector)
     return cmp(length(A), length(B))
 end
 
+"""
+    isless(A::AbstractArray{<:Any,0}, B::AbstractArray{<:Any,0})
+
+Return `true` when the only element of `A` is less than the only element of `B`.
+"""
+function isless(A::AbstractArray{<:Any,0}, B::AbstractArray{<:Any,0})
+    isless(only(A), only(B))
+end
+
 """
     isless(A::AbstractVector, B::AbstractVector)
 
diff --git a/test/arrayops.jl b/test/arrayops.jl
index ec8f54828b965..49d51176dcf71 100644
--- a/test/arrayops.jl
+++ b/test/arrayops.jl
@@ -1409,6 +1409,14 @@ end
 end
 
 @testset "lexicographic comparison" begin
+    @testset "zero-dimensional" begin
+        vals = (0, 0.0, 1, 1.0)
+        for l ∈ vals
+            for r ∈ vals
+                @test cmp(fill(l), fill(r)) == cmp(l, r)
+            end
+        end
+    end
     @test cmp([1.0], [1]) == 0
     @test cmp([1], [1.0]) == 0
     @test cmp([1, 1], [1, 1]) == 0