From 0c8eaa8d14b041e52cdc1ff1aa1efd256b9e7220 Mon Sep 17 00:00:00 2001
From: Michael Abbott <32575566+mcabbott@users.noreply.github.com>
Date: Wed, 5 Jan 2022 22:51:34 -0500
Subject: [PATCH] fix an empty case, add tests

---
 base/abstractarray.jl |  5 ++---
 test/arrayops.jl      | 10 ++++++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/base/abstractarray.jl b/base/abstractarray.jl
index fa37bc0b7dc1b..8b9f3217b930d 100644
--- a/base/abstractarray.jl
+++ b/base/abstractarray.jl
@@ -904,9 +904,8 @@ end
 
 function copyto!(dest::AbstractArray, dstart::Integer, src)
     i = Int(dstart)
-    if haslength(src)
-        checkbounds(dest, i)
-        checkbounds(dest, i + length(src) - 1)
+    if haslength(src) && length(dest) > 0
+        @boundscheck checkbounds(dest, i:(i + length(src) - 1))
         for x in src
             @inbounds dest[i] = x
             i += 1
diff --git a/test/arrayops.jl b/test/arrayops.jl
index 3e20a92a9d990..9ba28e862afe6 100644
--- a/test/arrayops.jl
+++ b/test/arrayops.jl
@@ -2122,6 +2122,16 @@ end
     @test_throws ArgumentError LinearAlgebra.copy_transpose!(a,2:3,1:3,b,1:5,2:7)
 end
 
+@testset "empty copyto!" begin
+    @test isempty(copyto!(Int[], ()))
+    @test isempty(copyto!(Int[], Int[]))
+    @test copyto!([1,2], ()) == [1,2]
+
+    @test isempty(copyto!(Int[], 1, ()))
+    @test isempty(copyto!(Int[], 1, Int[]))
+    @test copyto!([1,2], 1, ()) == [1,2]
+end
+
 module RetTypeDecl
     using Test
     import Base: +, *, broadcast, convert