From a2c2005b241fecd70b8aa92f02ff5c870394ca76 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Thu, 26 Nov 2020 19:58:15 +0000
Subject: [PATCH 01/11] add rrule

---
 src/rule_definition_tools.jl | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index 7026c0065..fc4f421f9 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -287,9 +287,7 @@ julia> frule((Zero(), 1), length, [2.0, 3.0])
 """
 macro non_differentiable(sig_expr)
     Meta.isexpr(sig_expr, :call) || error("Invalid use of `@non_differentiable`")
-    for arg in sig_expr.args
-        _isvararg(arg) && error("@non_differentiable does not support Varargs like: $arg")
-    end
+    has_vararg = _isvararg(sig_expr.args[end])
 
     primal_name, orig_args = Iterators.peel(sig_expr.args)
 
@@ -298,7 +296,13 @@ macro non_differentiable(sig_expr)
 
     unconstrained_args = _unconstrain.(constrained_args)
 
-    primal_invoke = :($(primal_name)($(unconstrained_args...); kwargs...))
+    primal_invoke = if !has_vararg
+        :($(primal_name)($(unconstrained_args...); kwargs...))
+    else
+        normal_args = unconstrained_args[1:end-1]
+        var_arg = unconstrained_args[end]
+        :($(primal_name)($(normal_args...), $(var_arg)...; kwargs...))
+    end
 
     quote
         $(_nondiff_frule_expr(primal_sig_parts, primal_invoke))
@@ -316,13 +320,22 @@ function _nondiff_frule_expr(primal_sig_parts, primal_invoke)
 end
 
 function _nondiff_rrule_expr(primal_sig_parts, primal_invoke)
-    num_primal_inputs = length(primal_sig_parts) - 1
+    has_vararg = _isvararg(primal_sig_parts[end])
+    if !has_vararg
+        num_primal_inputs = length(primal_sig_parts) - 1 # - primal
+        tup_expr = Expr(:tuple, NO_FIELDS, ntuple(_->DoesNotExist(), num_primal_inputs)...)
+    else
+        num_primal_inputs = length(primal_sig_parts) - 2 # - primal and vararg
+        length_expr = :(num_primal_inputs + length($(_unconstrain(primal_sig_parts[end]))))
+        tup_expr = Expr(:call, :ntuple, Expr(:(->), :_, DoesNotExist()), length_expr)
+    end
     primal_name = first(primal_invoke.args)
     pullback_expr = Expr(
         :function,
         Expr(:call, propagator_name(primal_name, :pullback), :_),
-        Expr(:tuple, NO_FIELDS, ntuple(_->DoesNotExist(), num_primal_inputs)...)
+        Expr(:tuple, NO_FIELDS, Expr(:(...), tup_expr))
     )
+    @show pullback_expr
     return esc(:(
         function ChainRulesCore.rrule($(primal_sig_parts...); kwargs...)
             return ($primal_invoke, $pullback_expr)

From e21ae1ae4838fe9c345f4b281f66f519e509bc0d Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Fri, 27 Nov 2020 14:36:27 +0000
Subject: [PATCH 02/11] fix vararg case

---
 src/rule_definition_tools.jl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index fc4f421f9..faedae0b3 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -323,10 +323,10 @@ function _nondiff_rrule_expr(primal_sig_parts, primal_invoke)
     has_vararg = _isvararg(primal_sig_parts[end])
     if !has_vararg
         num_primal_inputs = length(primal_sig_parts) - 1 # - primal
-        tup_expr = Expr(:tuple, NO_FIELDS, ntuple(_->DoesNotExist(), num_primal_inputs)...)
+        tup_expr = Expr(:tuple, ntuple(_->DoesNotExist(), num_primal_inputs)...)
     else
         num_primal_inputs = length(primal_sig_parts) - 2 # - primal and vararg
-        length_expr = :(num_primal_inputs + length($(_unconstrain(primal_sig_parts[end]))))
+        length_expr = :($(num_primal_inputs) + length($(_unconstrain(primal_sig_parts[end]))))
         tup_expr = Expr(:call, :ntuple, Expr(:(->), :_, DoesNotExist()), length_expr)
     end
     primal_name = first(primal_invoke.args)

From edfd3e5cc290a6714dff21a5b76ea78a93ca0095 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Fri, 27 Nov 2020 15:23:17 +0000
Subject: [PATCH 03/11] fix xs...

---
 src/rule_definition_tools.jl | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index faedae0b3..39cb9bf36 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -400,7 +400,8 @@ end
 "turn both `a` and `::constraint` into `a::constraint` etc"
 function _constrain_and_name(arg::Expr, _)
     Meta.isexpr(arg, :(::), 2) && return arg  # it is already fine.
-    Meta.isexpr(arg, :(::), 1) && return Expr(:(::), gensym(), arg.args[1])  #add name
+    Meta.isexpr(arg, :(::), 1) && return Expr(:(::), gensym(), arg.args[1]) # add name
+    Meta.isexpr(arg, :(...), 1) && return Expr(:(::), arg.args[1], :Vararg) # turn xs... into xs::Vararg
     error("malformed arguments: $arg")
 end
 _constrain_and_name(name::Symbol, constraint) = Expr(:(::), name, constraint)  # add type

From 0fdc605fc23352818c1ef6656a2c4a145eccef78 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Fri, 27 Nov 2020 15:24:31 +0000
Subject: [PATCH 04/11] remove tests for not supporting varargs

---
 test/rule_definition_tools.jl | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/test/rule_definition_tools.jl b/test/rule_definition_tools.jl
index 6ca7c769f..03a45e05a 100644
--- a/test/rule_definition_tools.jl
+++ b/test/rule_definition_tools.jl
@@ -126,10 +126,6 @@ end
         end
 
         @testset "Not supported (Yet)" begin
-            # Varargs are not supported
-            @test_macro_throws ErrorException @non_differentiable vararg1(xs...)
-            @test_macro_throws ErrorException @non_differentiable vararg1(xs::Vararg)
-
             # Where clauses are not supported.
             @test_macro_throws(
                 ErrorException,

From f68fdd76ad9c8b58eef5547bd72efd4983a816f3 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Fri, 27 Nov 2020 15:52:37 +0000
Subject: [PATCH 05/11] change the docstring

---
 src/rule_definition_tools.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index 39cb9bf36..1b31e03f3 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -281,7 +281,7 @@ julia> frule((Zero(), 1), length, [2.0, 3.0])
 
 !!! warning
     This helper macro covers only the simple common cases.
-    It does not support Varargs, or `where`-clauses.
+    It does not support `where`-clauses.
     For these you can declare the `rrule` and `frule` directly
 
 """

From a10696a5a993bed3a63e1e892e570f0b49b87c78 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Fri, 27 Nov 2020 16:19:32 +0000
Subject: [PATCH 06/11] add tests

---
 src/rule_definition_tools.jl  |  1 -
 test/rule_definition_tools.jl | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index 1b31e03f3..8d591fc4a 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -335,7 +335,6 @@ function _nondiff_rrule_expr(primal_sig_parts, primal_invoke)
         Expr(:call, propagator_name(primal_name, :pullback), :_),
         Expr(:tuple, NO_FIELDS, Expr(:(...), tup_expr))
     )
-    @show pullback_expr
     return esc(:(
         function ChainRulesCore.rrule($(primal_sig_parts...); kwargs...)
             return ($primal_invoke, $pullback_expr)
diff --git a/test/rule_definition_tools.jl b/test/rule_definition_tools.jl
index 03a45e05a..0beeba630 100644
--- a/test/rule_definition_tools.jl
+++ b/test/rule_definition_tools.jl
@@ -125,6 +125,39 @@ end
             @test rrule(NonDiffCounterExample, 2.0) === nothing
         end
 
+        @testset "Varargs" begin
+            fvarargs(a, xs...) = sum((a, xs...))
+            @testset "xs::Vararg{Int}" begin
+                @non_differentiable fvarargs(a, xs::Vararg{Int})
+
+                y, pb = rrule(fvarargs, 1)
+                @test y == fvarargs(1)
+                @test pb(1) == (Zero(), DoesNotExist())
+
+                y, pb = rrule(fvarargs, 1, 2, 3)
+                @test y == fvarargs(1, 2, 3)
+                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist(), DoesNotExist())
+
+                @test frule((1, 1), fvarargs, 1, 2) == (fvarargs(1, 2), DoesNotExist())
+
+                @test frule((1, 1), fvarargs, 1, 2.0) == nothing
+                @test rrule(fvarargs, 1, 2.0) == nothing
+            end
+            @testset "xs..." begin
+                @non_differentiable fvarargs(a, xs...)
+
+                y, pb = rrule(fvarargs, 1.)
+                @test y == fvarargs(1.)
+                @test pb(1) == (Zero(), DoesNotExist())
+
+                y, pb = rrule(fvarargs, 1, 2, 3)
+                @test y == fvarargs(1, 2, 3.)
+                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist(), DoesNotExist())
+
+                @test frule((1, 1.), fvarargs, 1, 2.) == (fvarargs(1, 2.), DoesNotExist())
+            end
+        end
+
         @testset "Not supported (Yet)" begin
             # Where clauses are not supported.
             @test_macro_throws(

From dc3d178438fda19c5d582ad97592b1510a1d956a Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Fri, 27 Nov 2020 16:26:31 +0000
Subject: [PATCH 07/11] bump patch

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

diff --git a/Project.toml b/Project.toml
index bbdecb05b..be7d74ad5 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "ChainRulesCore"
 uuid = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
-version = "0.9.19"
+version = "0.9.20"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

From db4ce02ece05563b2d626171d0577a2ec54d321a Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Mon, 30 Nov 2020 14:38:12 +0000
Subject: [PATCH 08/11] fix example from code-review

---
 src/rule_definition_tools.jl  | 10 ++++++----
 test/rule_definition_tools.jl | 14 ++++++++++++++
 test/runtests.jl              |  1 -
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index 8d591fc4a..1b6e991f4 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -300,8 +300,9 @@ macro non_differentiable(sig_expr)
         :($(primal_name)($(unconstrained_args...); kwargs...))
     else
         normal_args = unconstrained_args[1:end-1]
-        var_arg = unconstrained_args[end]
-        :($(primal_name)($(normal_args...), $(var_arg)...; kwargs...))
+        var_arg = unconstrained_args[end] # either `xs...`` or `xs`, coming from Vararg
+        var_arg_call = Meta.isexpr(var_arg, :(...), 1) ? var_arg : Expr(:(...), var_arg)
+        :($(primal_name)($(normal_args...), $(var_arg_call); kwargs...))
     end
 
     quote
@@ -393,6 +394,7 @@ end
 _unconstrain(arg::Symbol) = arg
 function _unconstrain(arg::Expr)
     Meta.isexpr(arg, :(::), 2) && return arg.args[1]  # drop constraint.
+    Meta.isexpr(arg, :(...), 1) && return Expr(:(...), _unconstrain(arg.args[1]))
     error("malformed arguments: $arg")
 end
 
@@ -400,7 +402,7 @@ end
 function _constrain_and_name(arg::Expr, _)
     Meta.isexpr(arg, :(::), 2) && return arg  # it is already fine.
     Meta.isexpr(arg, :(::), 1) && return Expr(:(::), gensym(), arg.args[1]) # add name
-    Meta.isexpr(arg, :(...), 1) && return Expr(:(::), arg.args[1], :Vararg) # turn xs... into xs::Vararg
+    Meta.isexpr(arg, :(...), 1) && return Expr(:(...), _constrain_and_name(arg.args[1], :Any))
     error("malformed arguments: $arg")
 end
-_constrain_and_name(name::Symbol, constraint) = Expr(:(::), name, constraint)  # add type
+_constrain_and_name(name::Symbol, constraint) = Expr(:(::), name, constraint)  # add type
\ No newline at end of file
diff --git a/test/rule_definition_tools.jl b/test/rule_definition_tools.jl
index 0beeba630..57a5f8b48 100644
--- a/test/rule_definition_tools.jl
+++ b/test/rule_definition_tools.jl
@@ -143,6 +143,20 @@ end
                 @test frule((1, 1), fvarargs, 1, 2.0) == nothing
                 @test rrule(fvarargs, 1, 2.0) == nothing
             end
+
+            @testset "::Float64..." begin
+                @non_differentiable fvarargs(a, ::Float64...)
+                
+                y, pb = rrule(fvarargs, 1.0, 1.0)
+                @test y == fvarargs(1.0, 1.0)
+                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist())
+
+                @test frule((1, 1), fvarargs, 1, 2.0) == (fvarargs(1, 2.0), DoesNotExist())
+
+                @test frule((1, 1, 1), fvarargs, 1, 1, 2.0) == nothing
+                @test rrule(fvarargs, 1, 1, 2.0) == nothing
+            end
+            
             @testset "xs..." begin
                 @non_differentiable fvarargs(a, xs...)
 
diff --git a/test/runtests.jl b/test/runtests.jl
index eab854b10..ed22f83c1 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -20,7 +20,6 @@ using Test
     include("rules.jl")
     include("rule_definition_tools.jl")
 
-
     @testset "demos" begin
         include("demos/forwarddiffzero.jl")
         include("demos/reversediffzero.jl")

From 5f36b03b50bbe6b721d0214a9334adf9fcdaa330 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Mon, 30 Nov 2020 16:00:06 +0000
Subject: [PATCH 09/11] more elegant solution and more complete tests

---
 src/rule_definition_tools.jl  |  7 +++---
 test/rule_definition_tools.jl | 42 ++++++++++++++---------------------
 2 files changed, 20 insertions(+), 29 deletions(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index 1b6e991f4..d783638f3 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -300,9 +300,8 @@ macro non_differentiable(sig_expr)
         :($(primal_name)($(unconstrained_args...); kwargs...))
     else
         normal_args = unconstrained_args[1:end-1]
-        var_arg = unconstrained_args[end] # either `xs...`` or `xs`, coming from Vararg
-        var_arg_call = Meta.isexpr(var_arg, :(...), 1) ? var_arg : Expr(:(...), var_arg)
-        :($(primal_name)($(normal_args...), $(var_arg_call); kwargs...))
+        var_arg = unconstrained_args[end]
+        :($(primal_name)($(normal_args...), $(var_arg)...; kwargs...))
     end
 
     quote
@@ -394,7 +393,7 @@ end
 _unconstrain(arg::Symbol) = arg
 function _unconstrain(arg::Expr)
     Meta.isexpr(arg, :(::), 2) && return arg.args[1]  # drop constraint.
-    Meta.isexpr(arg, :(...), 1) && return Expr(:(...), _unconstrain(arg.args[1]))
+    Meta.isexpr(arg, :(...), 1) && return _unconstrain(arg.args[1])
     error("malformed arguments: $arg")
 end
 
diff --git a/test/rule_definition_tools.jl b/test/rule_definition_tools.jl
index 57a5f8b48..cef6f9887 100644
--- a/test/rule_definition_tools.jl
+++ b/test/rule_definition_tools.jl
@@ -127,48 +127,40 @@ end
 
         @testset "Varargs" begin
             fvarargs(a, xs...) = sum((a, xs...))
-            @testset "xs::Vararg{Int}" begin
-                @non_differentiable fvarargs(a, xs::Vararg{Int})
+            @testset "xs::Float64..." begin
+                @non_differentiable fvarargs(a, xs::Float64...)
 
                 y, pb = rrule(fvarargs, 1)
                 @test y == fvarargs(1)
                 @test pb(1) == (Zero(), DoesNotExist())
 
-                y, pb = rrule(fvarargs, 1, 2, 3)
-                @test y == fvarargs(1, 2, 3)
+                y, pb = rrule(fvarargs, 1, 2.0, 3.0)
+                @test y == fvarargs(1, 2.0, 3.0)
                 @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist(), DoesNotExist())
 
-                @test frule((1, 1), fvarargs, 1, 2) == (fvarargs(1, 2), DoesNotExist())
+                @test frule((1, 1), fvarargs, 1, 2.0) == (fvarargs(1, 2.0), DoesNotExist())
 
-                @test frule((1, 1), fvarargs, 1, 2.0) == nothing
-                @test rrule(fvarargs, 1, 2.0) == nothing
+                @test frule((1, 1), fvarargs, 1, 2) == nothing
+                    @test rrule(fvarargs, 1, 2) == nothing
             end
 
             @testset "::Float64..." begin
                 @non_differentiable fvarargs(a, ::Float64...)
-                
-                y, pb = rrule(fvarargs, 1.0, 1.0)
-                @test y == fvarargs(1.0, 1.0)
-                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist())
 
-                @test frule((1, 1), fvarargs, 1, 2.0) == (fvarargs(1, 2.0), DoesNotExist())
+                y, pb = rrule(fvarargs, 1, 2.0, 3.0)
+                @test y == fvarargs(1, 2.0, 3.0)
+                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist(), DoesNotExist())
 
-                @test frule((1, 1, 1), fvarargs, 1, 1, 2.0) == nothing
-                @test rrule(fvarargs, 1, 1, 2.0) == nothing
+                @test frule((1, 1), fvarargs, 1, 2.0) == (fvarargs(1, 2.0), DoesNotExist())
             end
-            
-            @testset "xs..." begin
-                @non_differentiable fvarargs(a, xs...)
 
-                y, pb = rrule(fvarargs, 1.)
-                @test y == fvarargs(1.)
-                @test pb(1) == (Zero(), DoesNotExist())
-
-                y, pb = rrule(fvarargs, 1, 2, 3)
-                @test y == fvarargs(1, 2, 3.)
-                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist(), DoesNotExist())
+            @testset "::Vararg" begin
+                @non_differentiable fvarargs(a, ::Vararg)
+                @test frule((1, 1), fvarargs, 1, 2) == (fvarargs(1, 2), DoesNotExist())
 
-                @test frule((1, 1.), fvarargs, 1, 2.) == (fvarargs(1, 2.), DoesNotExist())
+                y, pb = rrule(fvarargs, 1, 1)
+                @test y == fvarargs(1, 1)
+                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist())
             end
         end
 

From 6620f80fcb2473bc521496541a519fe4306d1be1 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Tue, 1 Dec 2020 14:31:22 +0000
Subject: [PATCH 10/11] mini expr change

---
 src/rule_definition_tools.jl | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/rule_definition_tools.jl b/src/rule_definition_tools.jl
index d783638f3..7ff595ff5 100644
--- a/src/rule_definition_tools.jl
+++ b/src/rule_definition_tools.jl
@@ -319,16 +319,20 @@ function _nondiff_frule_expr(primal_sig_parts, primal_invoke)
     ))
 end
 
-function _nondiff_rrule_expr(primal_sig_parts, primal_invoke)
+function tuple_expression(primal_sig_parts)
     has_vararg = _isvararg(primal_sig_parts[end])
-    if !has_vararg
+    return if !has_vararg
         num_primal_inputs = length(primal_sig_parts) - 1 # - primal
-        tup_expr = Expr(:tuple, ntuple(_->DoesNotExist(), num_primal_inputs)...)
+        Expr(:tuple, ntuple(_->DoesNotExist(), num_primal_inputs)...)
     else
         num_primal_inputs = length(primal_sig_parts) - 2 # - primal and vararg
         length_expr = :($(num_primal_inputs) + length($(_unconstrain(primal_sig_parts[end]))))
-        tup_expr = Expr(:call, :ntuple, Expr(:(->), :_, DoesNotExist()), length_expr)
+        Expr(:call, :ntuple, Expr(:(->), :_, DoesNotExist()), length_expr)
     end
+end
+
+function _nondiff_rrule_expr(primal_sig_parts, primal_invoke)
+    tup_expr = tuple_expression(primal_sig_parts)
     primal_name = first(primal_invoke.args)
     pullback_expr = Expr(
         :function,

From 04aa23653002d36e3b7fa1ec7644e9625d9c3961 Mon Sep 17 00:00:00 2001
From: Miha Zgubic <miha.zgubic@invenialabs.co.uk>
Date: Tue, 1 Dec 2020 14:31:29 +0000
Subject: [PATCH 11/11] add two tests

---
 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 cef6f9887..c4a0df8d3 100644
--- a/test/rule_definition_tools.jl
+++ b/test/rule_definition_tools.jl
@@ -154,6 +154,16 @@ end
                 @test frule((1, 1), fvarargs, 1, 2.0) == (fvarargs(1, 2.0), DoesNotExist())
             end
 
+            @testset "::Vararg{Float64}" begin
+                @non_differentiable fvarargs(a, ::Vararg{Float64})
+
+                y, pb = rrule(fvarargs, 1, 2.0, 3.0)
+                @test y == fvarargs(1, 2.0, 3.0)
+                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist(), DoesNotExist())
+
+                @test frule((1, 1), fvarargs, 1, 2.0) == (fvarargs(1, 2.0), DoesNotExist())
+            end
+
             @testset "::Vararg" begin
                 @non_differentiable fvarargs(a, ::Vararg)
                 @test frule((1, 1), fvarargs, 1, 2) == (fvarargs(1, 2), DoesNotExist())
@@ -162,6 +172,15 @@ end
                 @test y == fvarargs(1, 1)
                 @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist())
             end
+
+            @testset "xs..." begin
+                @non_differentiable fvarargs(a, xs...)
+                @test frule((1, 1), fvarargs, 1, 2) == (fvarargs(1, 2), DoesNotExist())
+
+                y, pb = rrule(fvarargs, 1, 1)
+                @test y == fvarargs(1, 1)
+                @test pb(1) == (Zero(), DoesNotExist(), DoesNotExist())
+            end
         end
 
         @testset "Not supported (Yet)" begin