From 1d39d74831856478d3f8a753cce16aabf127a9f5 Mon Sep 17 00:00:00 2001
From: Sheehan Olver <solver@mac.com>
Date: Tue, 13 Oct 2026 19:41:16 +0100
Subject: [PATCH] Avoid reshape when materialising DualLayout views of matrices
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

`_dual_adjoint`/`_dual_transpose` assumed the parent of a `DualLayout` view
is an adjoint/transpose of a vector. When it is a 1×n matrix with
`DualLayout` (e.g. a `BlockedMatrix` wrapping an adjoint vector), the
adjoint is an n×1 matrix and linear indexing into it reshapes, which fails
for infinite arrays. Take a column view instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 Project.toml             |  2 +-
 src/memorylayout.jl      |  8 ++++++--
 test/test_layoutarray.jl | 18 ++++++++++++++++++
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/Project.toml b/Project.toml
index 6f723e6..de648e1 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "ArrayLayouts"
 uuid = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
-version = "1.16"
+version = "1.16.1"
 authors = ["Sheehan Olver <solver@mac.com>"]
 
 [deps]
diff --git a/src/memorylayout.jl b/src/memorylayout.jl
index 6f2263c..4375ce0 100644
--- a/src/memorylayout.jl
+++ b/src/memorylayout.jl
@@ -299,8 +299,12 @@ sublayout(::DualLayout{ML}, INDS::Type) where ML = sublayout(ML(), INDS)
 
 # try to maintain "type" of parent ie adjoint/transpose when materialising, even though layouts are equivalent
 # to preserve special overloads
-_dual_adjoint(a::SubArray{<:Any, 2, <:Any, <:Tuple{Slice,Any}}) = view(parent(a)', parentindices(a)[2])
-_dual_transpose(a::SubArray{<:Any, 2, <:Any, <:Tuple{Slice,Any}}) = view(transpose(parent(a)), parentindices(a)[2])
+# parent may be a 1×n matrix with DualLayout (e.g. a wrapper around an adjoint vector), in which case
+# we take a column view of its adjoint rather than linear indexing (which would reshape)
+_dual_view(v::AbstractVector, jr) = view(v, jr)
+_dual_view(A::AbstractMatrix, jr) = view(A, jr, only(axes(A,2)))
+_dual_adjoint(a::SubArray{<:Any, 2, <:Any, <:Tuple{Slice,Any}}) = _dual_view(parent(a)', parentindices(a)[2])
+_dual_transpose(a::SubArray{<:Any, 2, <:Any, <:Tuple{Slice,Any}}) = _dual_view(transpose(parent(a)), parentindices(a)[2])
 sub_materialize(::DualLayout{ML}, A::AbstractMatrix{<:Real}) where ML = sub_materialize(adjointlayout(eltype(A), ML()), _dual_adjoint(A))'
 sub_materialize(::DualLayout{ML}, A::AbstractMatrix) where ML<:ConjLayout = sub_materialize(adjointlayout(eltype(A), ML()), _dual_adjoint(A))'
 sub_materialize(::DualLayout{ML}, A::AbstractMatrix) where ML = transpose(sub_materialize(transposelayout(ML()), _dual_transpose(A)))
diff --git a/test/test_layoutarray.jl b/test/test_layoutarray.jl
index ffa2cf6..ad34e70 100644
--- a/test/test_layoutarray.jl
+++ b/test/test_layoutarray.jl
@@ -910,4 +910,22 @@ end
     @test transpose(lv) * F == transpose(v) * F
 end
 
+@testset "DualLayout matrix parent" begin
+    # a 1×n matrix with DualLayout that is not itself an adjoint vector
+    a = randn(5)
+    for (M, f) in ((MyMatrix(a'), adjoint), (MyMatrix(transpose(a)), transpose),
+                   (MyMatrix((a .+ im)'), adjoint), (MyMatrix(transpose(a .+ im)), transpose))
+        @test MemoryLayout(M) isa DualLayout
+        V = view(M, :, 1:3)
+        @test MemoryLayout(V) isa DualLayout
+        @test M[:,1:3] == f(f(M)[1:3])
+        # avoid linear indexing into a matrix, which reshapes
+        @test !(parent(ArrayLayouts._dual_adjoint(V)) isa Base.ReshapedArray)
+        @test !(parent(ArrayLayouts._dual_transpose(V)) isa Base.ReshapedArray)
+    end
+    # linear indexing into an infinite matrix is not supported, so must avoid reshape
+    M = MyMatrix(InfiniteArrays.InfVec()')
+    @test M[:,1:3] == M.A[:,1:3]
+end
+
 end