From e0ad7c622efd08eac459d9c67f95e7df9044d81d Mon Sep 17 00:00:00 2001
From: Carlo Lucibello <carlo.lucibello@gmail.com>
Date: Wed, 1 Sep 2021 06:01:20 +0200
Subject: [PATCH 1/3] rrule for fill!

---
 src/rulesets/Base/array.jl  | 12 ++++++++++++
 test/rulesets/Base/array.jl |  5 +++++
 2 files changed, 17 insertions(+)

diff --git a/src/rulesets/Base/array.jl b/src/rulesets/Base/array.jl
index eb05753d0..28e4fb959 100644
--- a/src/rulesets/Base/array.jl
+++ b/src/rulesets/Base/array.jl
@@ -342,3 +342,15 @@ function rrule(::typeof(fill), x::Any, dims...)
     fill_pullback(Ȳ) = (NoTangent(), project(sum(Ȳ)), nots...)
     return fill(x, dims...), fill_pullback
 end
+
+
+#####
+##### `fill!`
+#####
+
+function rrule(::typeof(fill!), A, x)
+    project = x isa Union{Number, AbstractArray{<:Number}} ? ProjectTo(x) : identity
+    fill!_pullback(Ȳ) = (NoTangent(), ZeroTangent(), project(sum(Ȳ)))
+    return fill!(A, x), fill!_pullback
+end
+
diff --git a/test/rulesets/Base/array.jl b/test/rulesets/Base/array.jl
index f601a0bb8..2cac0e503 100644
--- a/test/rulesets/Base/array.jl
+++ b/test/rulesets/Base/array.jl
@@ -198,3 +198,8 @@ end
     test_rrule(fill, 55 + 0.5im, 5)
     test_rrule(fill, 3.3, (3, 3, 3))
 end
+
+@testset "fill!" begin
+    test_rrule(fill!, rand(2), 1)
+    test_rrule(fill!, rand(2) + im*rand(2), 1)
+end

From 7c5ef0d22e0fec9ba0dbe3c3dc8199bb7ceff2e4 Mon Sep 17 00:00:00 2001
From: Carlo Lucibello <carlo.lucibello@gmail.com>
Date: Wed, 1 Sep 2021 06:03:03 +0200
Subject: [PATCH 2/3] cleanup

---
 src/rulesets/Base/array.jl | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/rulesets/Base/array.jl b/src/rulesets/Base/array.jl
index 28e4fb959..607a6d39a 100644
--- a/src/rulesets/Base/array.jl
+++ b/src/rulesets/Base/array.jl
@@ -343,7 +343,6 @@ function rrule(::typeof(fill), x::Any, dims...)
     return fill(x, dims...), fill_pullback
 end
 
-
 #####
 ##### `fill!`
 #####

From 20c65bbb975dcedea1001a6dece360fe336e150f Mon Sep 17 00:00:00 2001
From: Carlo Lucibello <carlo.lucibello@gmail.com>
Date: Wed, 1 Sep 2021 06:04:28 +0200
Subject: [PATCH 3/3] bump version

---
 Project.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Project.toml b/Project.toml
index ee1a2a877..3c1473b07 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.11.3"
+version = "1.12.0"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"