use ismutabletype from Compat

Author: oxinabox

Project.toml

@@ -7,20 +7,17 @@ Compat = "34da2185-b29b-5c13-b0c7-acf172513d20"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 
-[weakdeps]
-SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
-
-[extensions]
-ChainRulesCoreSparseArraysExt = "SparseArrays"
-
 [compat]
 BenchmarkTools = "0.5"
-Compat = "2, 3, 4"
+Compat = "3.40, 4"
 FiniteDifferences = "0.10"
 OffsetArrays = "1"
 StaticArrays = "0.11, 0.12, 1"
 julia = "1.6"
 
+[extensions]
+ChainRulesCoreSparseArraysExt = "SparseArrays"
+
 [extras]
 BenchmarkTools = "6e4b80f9-dd63-53aa-95a3-0cdb28fa8baf"
 FiniteDifferences = "26cc04aa-876d-5657-8c51-4c34ba976000"
@@ -31,3 +28,6 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
 test = ["Test", "BenchmarkTools", "FiniteDifferences", "OffsetArrays", "SparseArrays", "StaticArrays"]
+
+[weakdeps]
+SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"

src/ChainRulesCore.jl

@@ -2,7 +2,7 @@ module ChainRulesCore
 using Base.Broadcast: broadcasted, Broadcasted, broadcastable, materialize, materialize!
 using Base.Meta
 using LinearAlgebra
-using Compat: hasfield, hasproperty
+using Compat: hasfield, hasproperty, ismutabletype
 
 export frule, rrule  # core function
 # rule configurations