From 3f8d86f40548c11aa5c543d65ec973cf4bb59767 Mon Sep 17 00:00:00 2001
From: mtfishman <mfishman@flatironinstitute.org>
Date: Thu, 8 Jan 2026 13:12:02 -0500
Subject: [PATCH] Fix mixing sparse and dense styles

---
 Project.toml                    |  2 +-
 src/abstractsparsearraystyle.jl |  7 +++++++
 test/test_sparse_style.jl       | 12 ++++++++++--
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/Project.toml b/Project.toml
index 65ec019..57d785d 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "SparseArraysBase"
 uuid = "0d5efcca-f356-4864-8770-e1ed8d78f208"
 authors = ["ITensor developers <support@itensor.org> and contributors"]
-version = "0.8.2"
+version = "0.8.3"
 
 [deps]
 Accessors = "7d9f7c33-5ae7-4f3b-8dc6-eff91059b697"
diff --git a/src/abstractsparsearraystyle.jl b/src/abstractsparsearraystyle.jl
index 24c1f08..0411b63 100644
--- a/src/abstractsparsearraystyle.jl
+++ b/src/abstractsparsearraystyle.jl
@@ -67,6 +67,13 @@ function FunctionImplementations.Style(
     )
     return style1
 end
+# Fix ambiguity error with `Style(::AbstractSparseArrayStyle, ::AbstractArrayStyle)`.
+using FunctionImplementations: DefaultArrayStyle
+function FunctionImplementations.Style(
+        style1::AbstractSparseArrayStyle, style2::DefaultArrayStyle
+    )
+    return style1
+end
 
 to_vec(x) = vec(collect(x))
 to_vec(x::AbstractArray) = vec(x)
diff --git a/test/test_sparse_style.jl b/test/test_sparse_style.jl
index 9463607..735b202 100644
--- a/test/test_sparse_style.jl
+++ b/test/test_sparse_style.jl
@@ -1,5 +1,6 @@
-using FunctionImplementations: Style, style
-using SparseArraysBase: AbstractSparseArrayStyle, SparseArrayStyle, sparse_style, sparsezeros
+using FunctionImplementations: DefaultArrayStyle, Style, style
+using SparseArraysBase: AbstractSparseArrayStyle, SparseArrayStyle, sparse_style,
+    sparsezeros
 using Test: @test, @testset
 
 module TestSparseStyleUtils
@@ -23,4 +24,11 @@ end
         TestSparseStyleUtils.MySparseArrayStyle()
     @test style(sparsezeros(2, 2), TestSparseStyleUtils.MySparseArray{Float64, 2}((2, 2))) ≡
         SparseArrayStyle()
+
+    # Regression tests for ambiguity caused by combining AbstractSparseArrayStyle with
+    # DefaultArrayStyle.
+    @test Style(TestSparseStyleUtils.MySparseArrayStyle(), DefaultArrayStyle()) ≡
+        TestSparseStyleUtils.MySparseArrayStyle()
+    @test style(TestSparseStyleUtils.MySparseArray{Float64, 2}((2, 2)), randn(2, 2)) ≡
+        TestSparseStyleUtils.MySparseArrayStyle()
 end