From eefb6618dfe8fc7ff8af643b8635c80b908aa674 Mon Sep 17 00:00:00 2001
From: Tor Erlend Fjelde <tor.erlend95@gmail.com>
Date: Sat, 31 Jul 2021 10:52:32 +0100
Subject: [PATCH 1/2] use gensym for lens in setmacro

---
 src/sugar.jl | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/sugar.jl b/src/sugar.jl
index 11a812f..377fa06 100644
--- a/src/sugar.jl
+++ b/src/sugar.jl
@@ -174,19 +174,20 @@ function setmacro(lenstransform, ex::Expr; overwrite::Bool=false)
     @assert length(ex.args) == 2
     ref, val = ex.args
     obj, lens = parse_obj_lens(ref)
+    lenssym = gensym(:lens)
     dst = overwrite ? obj : gensym("_")
     val = esc(val)
     ret = if ex.head == :(=)
         quote
-            lens = ($lenstransform)($lens)
-            $dst = $set($obj, lens, $val)
+            $lenssym = ($lenstransform)($lens)
+            $dst = $set($obj, $lenssym, $val)
         end
     else
         op = get_update_op(ex.head)
         f = :($_UpdateOp($op,$val))
         quote
-            lens = ($lenstransform)($lens)
-            $dst = $modify($f, $obj, lens)
+            $lenssym = ($lenstransform)($lens)
+            $dst = $modify($f, $obj, $lenssym)
         end
     end
     ret

From cb1d984ae3b39d1c3e52cf92beed40a26a1b04b0 Mon Sep 17 00:00:00 2001
From: Tor Erlend Fjelde <tor.erlend95@gmail.com>
Date: Sun, 1 Aug 2021 05:34:47 +0100
Subject: [PATCH 2/2] added test for type inference with multiple usage of
 setmacro within the same macro

---
 test/test_setmacro.jl | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/test/test_setmacro.jl b/test/test_setmacro.jl
index bc48fa3..77c9bb0 100644
--- a/test/test_setmacro.jl
+++ b/test/test_setmacro.jl
@@ -46,5 +46,31 @@ using StaticNumbers
     @test m3 === @SMatrix[1 0; 0 0]
 end
 
+function test_all_inferrable(f, argtypes)
+    typed = first(code_typed(f, argtypes))
+    code = typed.first
+    @test all(T -> !(T isa UnionAll || T === Any), code.slottypes)
+end
+
+# Example of macro that caused inference issues before.
+macro test_macro(expr)
+    quote
+        function f($(esc(:x)))
+            $(Setfield.setmacro(identity, expr, overwrite=true))
+            $(Setfield.setmacro(identity, expr, overwrite=true))
+            $(Setfield.setmacro(identity, expr, overwrite=true))
+            $(Setfield.setmacro(identity, expr, overwrite=true))
+            $(Setfield.setmacro(identity, expr, overwrite=true))
+            return $(esc(:x))
+        end
+    end
+end
+
+@testset "setmacro multiple usage" begin
+    let f = @test_macro(x[end] = 1)
+        test_all_inferrable(f, (Vector{Float64}, ))
+    end
+end
+
 end#module