Revert "Remove Compat dependency and use a test workspace"

This reverts commit 03ff6dd.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: devmotion

.github/dependabot.yml

@@ -6,7 +6,8 @@ updates:
     schedule:
       interval: "weekly"
   - package-ecosystem: "julia"
-    directory: "/"
+    directories:
+      - "/"
     schedule:
       interval: "weekly"
     groups:

Project.toml

@@ -1,10 +1,11 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.74.2"
+version = "1.74.1"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
+Compat = "34da2185-b29b-5c13-b0c7-acf172513d20"
 Distributed = "8ba89e20-285c-5b6f-9357-94700520ee1b"
 GPUArraysCore = "46192b85-c4d5-4398-a991-12ede77f4527"
 IrrationalConstants = "92d709cd-6900-40b7-9082-c6be49f344b6"
@@ -20,6 +21,7 @@ StructArrays = "09ab397b-f2b6-538f-b94a-2f83cf4a842a"
 Adapt = "3.4.0, 4"
 ChainRulesCore = "1.25"
 ChainRulesTestUtils = "1.5"
+Compat = "3.46, 4.2"
 Distributed = "1"
 FiniteDifferences = "0.12.20"
 GPUArraysCore = "0.1.0, 0.2"
@@ -47,6 +49,3 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
 test = ["ChainRulesTestUtils", "FiniteDifferences", "JLArrays", "ParallelTestRunner", "Random", "StaticArrays", "Test"]
-
-[workspace]
-projects = ["test"]

src/ChainRules.jl

@@ -3,6 +3,7 @@ module ChainRules
 using Adapt: adapt
 using Base.Broadcast: materialize, materialize!, broadcasted, Broadcasted, broadcastable
 using ChainRulesCore
+using Compat
 using Distributed
 using GPUArraysCore: AbstractGPUArray, AbstractGPUArrayStyle, @allowscalar
 using IrrationalConstants: logtwo, logten
@@ -21,6 +22,8 @@ import ChainRulesCore: rrule, frule
 # Experimental:
 using ChainRulesCore: derivatives_given_output
 
+using Compat: stack
+
 # numbers that we know commute under multiplication
 const CommutativeMulNumber = Union{Real,Complex}