From 6a8e46141cec083758adecffc218fca420b59ffc Mon Sep 17 00:00:00 2001
From: William Moses <gh@wsmoses.com>
Date: Wed, 27 Nov 2024 12:12:22 -0500
Subject: [PATCH] simplify deferred failures (#2126)

Co-authored-by: William Moses <wsmoses@cyclops.juliacomputing.io>
---
 src/Enzyme.jl   | 9 ++++++---
 src/compiler.jl | 2 +-
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/Enzyme.jl b/src/Enzyme.jl
index 5305beff8d..8c94911368 100644
--- a/src/Enzyme.jl
+++ b/src/Enzyme.jl
@@ -690,13 +690,13 @@ code, as well as high-order differentiation.
         rt = Compiler.primal_return_type(mode, FTy, tt)
         A2 = A{rt}
         if rt == Union{}
-            throw(ErrorException("Return type inferred to be Union{}. Giving up."))
+            rt = Nothing 
         end
     else
         @assert A isa DataType
         rt = A
         if rt == Union{}
-	          throw(ErrorException("Return type inferred to be Union{}. Giving up."))
+	    throw(ErrorException("Return type inferred to be Union{}. Giving up."))
         end
     end
 
@@ -841,7 +841,10 @@ code, as well as high-order differentiation.
 
     if RT isa UnionAll
         rt = Compiler.primal_return_type(mode, FT, tt)
-        rt = RT{rt}
+	if rt == Union{}
+	   rt = Nothing
+	end
+	rt = RT{rt}
     else
         @assert RT isa DataType
         rt = RT
diff --git a/src/compiler.jl b/src/compiler.jl
index e836f4bb8c..f266fd5f34 100644
--- a/src/compiler.jl
+++ b/src/compiler.jl
@@ -3262,7 +3262,7 @@ function primal_return_type_generator(world::UInt, source, self, @nospecialize(m
     return new_ci
 end
 
-@eval @inline function primal_return_type(mode::Mode, ft::Type, tt::Type)
+@eval Base.@assume_effects :removable :foldable :nothrow @inline function primal_return_type(mode::Mode, ft::Type, tt::Type)
     $(Expr(:meta, :generated_only))
     $(Expr(:meta, :generated, primal_return_type_generator))
 end