From e7e54b1527124d923da1da85785e2faee2c8e4c3 Mon Sep 17 00:00:00 2001
From: Lyndon White <lyndon.white@invenialabs.co.uk>
Date: Tue, 12 Jan 2021 14:49:19 +0000
Subject: [PATCH 1/4] make creation of inputs to propagation consistently
 hyginic

---
 src/rule_definition_tools.jl | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index b68717693..e9accdcf4 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -142,7 +142,7 @@ function scalar_frule_expr(f, call, setup_stmts, inputs, partials)
 
     # Δs is the input to the propagator rule
     # because this is push-forward there is one per input to the function
-    Δs = [esc(Symbol(:Δ, i)) for i in 1:n_inputs]
+    Δs = _propagator_inputs(n_inputs)
     pushforward_returns = map(1:n_outputs) do output_i
         ∂s = partials[output_i].args
         propagation_expr(Δs, ∂s)
@@ -173,7 +173,7 @@ function scalar_rrule_expr(f, call, setup_stmts, inputs, partials)
 
     # Δs is the input to the propagator rule
     # because this is a pull-back there is one per output of function
-    Δs = [Symbol(:Δ, i) for i in 1:n_outputs]
+    Δs = _propagator_inputs(n_outputs)
 
     # 1 partial derivative per input
     pullback_returns = map(1:n_inputs) do input_i
@@ -198,6 +198,9 @@ function scalar_rrule_expr(f, call, setup_stmts, inputs, partials)
     end
 end
 
+"Declares properly hygenic inputs for propagation expressions"
+_propagator_inputs(n) = [esc(gensym(Symbol(:Δ, i))) for i in 1:n]
+
 """
     propagation_expr(Δs, ∂s, _conj = false)
 

From 836332662c418c0cbae190fabf30795ef42b7a8c Mon Sep 17 00:00:00 2001
From: Lyndon White <oxinabox@ucc.asn.au>
Date: Tue, 12 Jan 2021 15:18:18 +0000
Subject: [PATCH 2/4] Update src/rule_definition_tools.jl

Co-authored-by: Nick Robinson <npr251@gmail.com>
---
 src/rule_definition_tools.jl | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index e9accdcf4..b56d4415b 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -198,6 +198,8 @@ function scalar_rrule_expr(f, call, setup_stmts, inputs, partials)
     end
 end
 
+# For context on why this is important, see 
+# https://github.com/JuliaDiff/ChainRulesCore.jl/pull/276
 "Declares properly hygenic inputs for propagation expressions"
 _propagator_inputs(n) = [esc(gensym(Symbol(:Δ, i))) for i in 1:n]
 

From f2b0b7f202b5be16f28987a015dfebcc146ba82f Mon Sep 17 00:00:00 2001
From: Lyndon White <lyndon.white@invenialabs.co.uk>
Date: Tue, 12 Jan 2021 15:42:30 +0000
Subject: [PATCH 3/4] add regression test against #276

---
 test/rule_definition_tools.jl | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/test/rule_definition_tools.jl b/test/rule_definition_tools.jl
index c4a0df8d3..35a2ddd88 100644
--- a/test/rule_definition_tools.jl
+++ b/test/rule_definition_tools.jl
@@ -207,5 +207,24 @@ end
             # make sure type is exactly as expected:
             @test ẏ isa Composite{Tuple{Irrational{:π}, Float64}, Tuple{Float32, Float32}}
         end
+
+        @testset "Regression test against #276" begin
+            # https://github.com/JuliaDiff/ChainRulesCore.jl/pull/276
+            # Symptom of this problem is creation of global variables and type instablily
+
+            num_globals_before = length(names(ChainRulesCore; all=true))
+
+            simo2(x) = (x, 2x)
+            @scalar_rule(simo2(x), 1.0, 2.0)
+            _, simo2_pb = rrule(simo2, 43.0)
+            # make sure it infers: inferability implies type stability
+            @inferred simo2_pb(Composite{Tuple{Float64, Float64}}(3.0, 6.0))
+
+            # Test no new globals were created
+            @test length(names(ChainRulesCore; all=true)) == num_globals_before
+        end
     end
+
+
+
 end

From 00ef4f67cbbc45b75f118971f35361d37c3c1e55 Mon Sep 17 00:00:00 2001
From: Lyndon White <lyndon.white@invenialabs.co.uk>
Date: Tue, 12 Jan 2021 16:22:36 +0000
Subject: [PATCH 4/4] bump version

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

diff --git a/Project.toml b/Project.toml
index d4bcbd5d8..185d3f722 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "ChainRulesCore"
 uuid = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
-version = "0.9.24"
+version = "0.9.25"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"