From 371824ef7620c0d64fcb16140709806a588c7a62 Mon Sep 17 00:00:00 2001
From: Joshua Lampert <joshua.lampert@uni-hamburg.de>
Date: Thu, 5 Mar 2026 17:18:02 +0100
Subject: [PATCH] fix recursivecopy! for mixed nested VectorOfArray

---
 src/utils.jl       |  8 ++++----
 test/utils_test.jl | 10 ++++++++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/utils.jl b/src/utils.jl
index 68916f91..4f8b942e 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -95,12 +95,12 @@ function recursivecopy!(
 end
 
 function recursivecopy!(b::AbstractVectorOfArray, a::AbstractVectorOfArray)
-    if ArrayInterface.ismutable(eltype(b.u))
-        @inbounds for i in eachindex(b.u, a.u)
+    @inbounds for i in eachindex(b.u, a.u)
+        if ArrayInterface.ismutable(b.u[i]) || b.u[i] isa AbstractVectorOfArray
             recursivecopy!(b.u[i], a.u[i])
+        else
+            b.u[i] = recursivecopy(a.u[i])
         end
-    else
-        copyto!(b.u, a.u)
     end
     return b
 end
diff --git a/test/utils_test.jl b/test/utils_test.jl
index d3bb349d..07ba9df5 100644
--- a/test/utils_test.jl
+++ b/test/utils_test.jl
@@ -139,6 +139,16 @@ end
     @test u1.u[2] == [2.0, 2.0]
     @test u1.u[1] isa SVector
     @test u1.u[2] isa SVector
+
+    # mixed/nested partition types create a Union eltype for `u`.
+    # recursivecopy! must not fall back to a shallow copy in this case.
+    a = VectorOfArray([ones(2), VectorOfArray([1.0, 1.0])])
+    b = recursivecopy(a)
+    recursivecopy!(b, a)
+    @test !(b.u[1] === a.u[1])
+    @test !(b.u[2] === a.u[2])
+    b.u[1][1] = 99.0
+    @test a.u[1][1] == 1.0
 end
 
 # Test recursivefill! with immutable StaticArrays (issue #461)