From d53d943e15494550145045e909fc9cda5937ab62 Mon Sep 17 00:00:00 2001
From: Guillaume Dalle <22795598+gdalle@users.noreply.github.com>
Date: Fri, 9 May 2025 19:46:38 +0200
Subject: [PATCH 1/6] feat: error hints for Enzyme

---
 DifferentiationInterface/CHANGELOG.md         | 11 ++++-
 DifferentiationInterface/Project.toml         |  4 +-
 .../DifferentiationInterfaceEnzymeExt.jl      |  3 ++
 .../DifferentiationInterfaceEnzymeExt/init.jl | 44 +++++++++++++++++++
 4 files changed, 58 insertions(+), 4 deletions(-)
 create mode 100644 DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl

diff --git a/DifferentiationInterface/CHANGELOG.md b/DifferentiationInterface/CHANGELOG.md
index 7682ef9b4..9ec766c29 100644
--- a/DifferentiationInterface/CHANGELOG.md
+++ b/DifferentiationInterface/CHANGELOG.md
@@ -7,13 +7,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-### Changed
+## [0.6.54] - 2025-05-07
 
-- Allocate Enzyme shadow memory during preparation ([#782])
+### Added
+
+- Error hints for Enzyme ([#788])
 
 ## [0.6.53] - 2025-05-07
 
+### Changed
+
+- Allocate Enzyme shadow memory during preparation ([#782])
+
 [unreleased]: https://github.com/JuliaDiff/DifferentiationInterface.jl/compare/DifferentiationInterface-v0.6.53...main
 [0.6.53]: https://github.com/JuliaDiff/DifferentiationInterface.jl/compare/DifferentiationInterface-v0.6.52...DifferentiationInterface-v0.6.53
 
+[#788]: https://github.com/JuliaDiff/DifferentiationInterface.jl/pull/788
 [#782]: https://github.com/JuliaDiff/DifferentiationInterface.jl/pull/782
\ No newline at end of file
diff --git a/DifferentiationInterface/Project.toml b/DifferentiationInterface/Project.toml
index 852718e42..ab28e08c0 100644
--- a/DifferentiationInterface/Project.toml
+++ b/DifferentiationInterface/Project.toml
@@ -1,7 +1,7 @@
 name = "DifferentiationInterface"
 uuid = "a0c0ee7d-e4b9-4e03-894e-1c5f64a51d63"
 authors = ["Guillaume Dalle", "Adrian Hill"]
-version = "0.6.53"
+version = "0.6.54"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"
@@ -56,7 +56,7 @@ ADTypes = "1.13.0"
 ChainRulesCore = "1.23.0"
 DiffResults = "1.1.0"
 Diffractor = "=0.2.6"
-Enzyme = "0.13.17"
+Enzyme = "0.13.39"
 EnzymeCore = "0.8.8"
 ExplicitImports = "1.10.1"
 FastDifferentiation = "0.4.3"
diff --git a/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/DifferentiationInterfaceEnzymeExt.jl b/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/DifferentiationInterfaceEnzymeExt.jl
index 328bffaf3..dbf1e4f5c 100644
--- a/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/DifferentiationInterfaceEnzymeExt.jl
+++ b/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/DifferentiationInterfaceEnzymeExt.jl
@@ -30,6 +30,7 @@ using EnzymeCore:
     Split,
     WithPrimal
 using Enzyme:
+    Enzyme,
     autodiff,
     autodiff_thunk,
     create_shadows,
@@ -53,4 +54,6 @@ include("forward_twoarg.jl")
 include("reverse_onearg.jl")
 include("reverse_twoarg.jl")
 
+include("init.jl")
+
 end # module
diff --git a/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl b/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl
new file mode 100644
index 000000000..ebf59c14a
--- /dev/null
+++ b/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl
@@ -0,0 +1,44 @@
+function __init__()
+    # robust against internal changes
+    condition = (
+        isdefined(Enzyme, :Compiler) &&
+        Enzyme.Compiler isa Module &&
+        isdefined(Enzyme.Compiler, :EnzymeError) &&
+        Enzyme.Compiler.EnzymeError isa DataType
+    )
+    condition || return nothing
+    # see https://github.com/JuliaLang/julia/issues/58367 for why this isn't easier
+    for n in names(Enzyme.Compiler; all=true)
+        T = getfield(Enzyme.Compiler, n)
+        if T isa DataType && T <: Enzyme.Compiler.EnzymeError
+            # robust against internal changes
+            Base.Experimental.register_error_hint(T) do io, exc
+                if occursin("EnzymeMutabilityException", string(nameof(T)))
+                    printstyled(
+                        io,
+                        "\nIf you are using Enzyme through DifferentiationInterface, you may want to try modifying the ADTypes backend object as follows:";
+                        bold=true,
+                    )
+                    printstyled(
+                        io,
+                        "\n\n\tAutoEnzyme(; function_annotation=Enzyme.Duplicated)\n\n";
+                        color=:cyan,
+                        bold=true,
+                    )
+                elseif occursin("EnzymeRuntimeActivityError", string(nameof(T)))
+                    printstyled(
+                        io,
+                        "\nIf you are using Enzyme through DifferentiationInterface, you may want to try modifying the ADTypes backend object as follows:";
+                        bold=true,
+                    )
+                    printstyled(
+                        io,
+                        "\n\n\tAutoEnzyme(; mode=Enzyme.set_runtime_activity(Enzyme.Forward))\n\tAutoEnzyme(; mode=Enzyme.set_runtime_activity(Enzyme.Reverse))\n\n";
+                        color=:cyan,
+                        bold=true,
+                    )
+                end
+            end
+        end
+    end
+end

From 52a91fe9188a4e1853463555560133309d50a853 Mon Sep 17 00:00:00 2001
From: Guillaume Dalle <22795598+gdalle@users.noreply.github.com>
Date: Sat, 10 May 2025 07:10:25 +0200
Subject: [PATCH 2/6] Clearer message

---
 .../DifferentiationInterfaceEnzymeExt/init.jl | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl b/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl
index ebf59c14a..7681e49c0 100644
--- a/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl
+++ b/DifferentiationInterface/ext/DifferentiationInterfaceEnzymeExt/init.jl
@@ -1,3 +1,9 @@
+const HINT_END = "\n\nThis hint appears because DifferentiationInterface and Enzyme are both loaded. It does not necessarily imply that Enzyme is being called through DifferentiationInterface.\n\n"
+
+function HINT_START(option)
+    return "\nIf you are using Enzyme by selecting the `AutoEnzyme` object from ADTypes, you may want to try setting the `$option` option as follows:"
+end
+
 function __init__()
     # robust against internal changes
     condition = (
@@ -14,29 +20,23 @@ function __init__()
             # robust against internal changes
             Base.Experimental.register_error_hint(T) do io, exc
                 if occursin("EnzymeMutabilityException", string(nameof(T)))
+                    printstyled(io, HINT_START("function_annotation"); bold=true)
                     printstyled(
                         io,
-                        "\nIf you are using Enzyme through DifferentiationInterface, you may want to try modifying the ADTypes backend object as follows:";
-                        bold=true,
-                    )
-                    printstyled(
-                        io,
-                        "\n\n\tAutoEnzyme(; function_annotation=Enzyme.Duplicated)\n\n";
+                        "\n\n\tAutoEnzyme(; function_annotation=Enzyme.Duplicated)";
                         color=:cyan,
                         bold=true,
                     )
+                    printstyled(io, HINT_END; italic=true)
                 elseif occursin("EnzymeRuntimeActivityError", string(nameof(T)))
+                    printstyled(io, HINT_START("mode"); bold=true)
                     printstyled(
                         io,
-                        "\nIf you are using Enzyme through DifferentiationInterface, you may want to try modifying the ADTypes backend object as follows:";
-                        bold=true,
-                    )
-                    printstyled(
-                        io,
-                        "\n\n\tAutoEnzyme(; mode=Enzyme.set_runtime_activity(Enzyme.Forward))\n\tAutoEnzyme(; mode=Enzyme.set_runtime_activity(Enzyme.Reverse))\n\n";
+                        "\n\n\tAutoEnzyme(; mode=Enzyme.set_runtime_activity(Enzyme.Forward))\n\tAutoEnzyme(; mode=Enzyme.set_runtime_activity(Enzyme.Reverse))";
                         color=:cyan,
                         bold=true,
                     )
+                    printstyled(io, HINT_END; italic=true)
                 end
             end
         end

From 9ceeb97a97caafee41a3a0bb6fbfbe2c91276013 Mon Sep 17 00:00:00 2001
From: Guillaume Dalle <22795598+gdalle@users.noreply.github.com>
Date: Sat, 10 May 2025 07:30:48 +0200
Subject: [PATCH 3/6] Add tests

---
 .../test/Back/Enzyme/hints.jl                 | 56 +++++++++++++++++++
 .../test/Core/Internals/hints.jl              | 15 +++++
 2 files changed, 71 insertions(+)
 create mode 100644 DifferentiationInterface/test/Back/Enzyme/hints.jl
 create mode 100644 DifferentiationInterface/test/Core/Internals/hints.jl

diff --git a/DifferentiationInterface/test/Back/Enzyme/hints.jl b/DifferentiationInterface/test/Back/Enzyme/hints.jl
new file mode 100644
index 000000000..a6d5a3742
--- /dev/null
+++ b/DifferentiationInterface/test/Back/Enzyme/hints.jl
@@ -0,0 +1,56 @@
+using DifferentiationInterface
+using Enzyme: Enzyme
+using Test
+
+@testset "MutabilityError" begin
+    f = let
+        cache = [0.0]
+        x -> sum(copyto!(cache, x))
+    end
+
+    msg = try
+        gradient(f, AutoEnzyme(), [1.0])
+    catch e
+        buf = IOBuffer()
+        showerror(buf, e)
+        String(take!(buf))
+    end
+    @test occursin("AutoEnzyme", msg)
+    @test occursin("function_annotation", msg)
+    @test occursin("ADTypes", msg)
+    @test occursin("DifferentiationInterface", msg)
+end
+
+@testset "RuntimeActivityError" begin
+    function g(active_var, constant_var, cond)
+        if cond
+            return active_var
+        else
+            return constant_var
+        end
+    end
+
+    function h(active_var, constant_var, cond)
+        return [g(active_var, constant_var, cond), g(active_var, constant_var, cond)]
+    end
+
+    msg = try
+        pushforward(
+            h,
+            AutoEnzyme(; mode=Enzyme.Forward),
+            [1.0],
+            ([1.0],),
+            Constant([1.0]),
+            Constant(true),
+        )
+    catch e
+        buf = IOBuffer()
+        showerror(buf, e)
+        String(take!(buf))
+    end
+    @test occursin("AutoEnzyme", msg)
+    @test occursin("mode", msg)
+    @test occursin("set_runtime_activity", msg)
+    @test occursin("ADTypes", msg)
+    @test occursin("DifferentiationInterface", msg)
+end
diff --git a/DifferentiationInterface/test/Core/Internals/hints.jl b/DifferentiationInterface/test/Core/Internals/hints.jl
new file mode 100644
index 000000000..754782730
--- /dev/null
+++ b/DifferentiationInterface/test/Core/Internals/hints.jl
@@ -0,0 +1,15 @@
+using ADTypes
+using DifferentiationInterface
+import DifferentiationInterface as DI
+using Test
+
+@testset "Missing backend" begin
+    msg = try
+        gradient(sum, AutoZygote(), [1.0])
+    catch e
+        buf = IOBuffer()
+        showerror(buf, e)
+        String(take!(buf))
+    end
+    @test occursin("import Zygote", msg)
+end

From 8f226610e1e21943f7335dc6696351d8a8218b51 Mon Sep 17 00:00:00 2001
From: Guillaume Dalle <22795598+gdalle@users.noreply.github.com>
Date: Sat, 10 May 2025 07:34:00 +0200
Subject: [PATCH 4/6] Simpler show

---
 DifferentiationInterface/test/Back/Enzyme/hints.jl | 14 ++++++--------
 .../test/Core/Internals/hints.jl                   |  7 +++----
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/DifferentiationInterface/test/Back/Enzyme/hints.jl b/DifferentiationInterface/test/Back/Enzyme/hints.jl
index a6d5a3742..5a11c6b07 100644
--- a/DifferentiationInterface/test/Back/Enzyme/hints.jl
+++ b/DifferentiationInterface/test/Back/Enzyme/hints.jl
@@ -8,13 +8,12 @@ using Test
         x -> sum(copyto!(cache, x))
     end
 
-    msg = try
+    e = nothing
+    try
         gradient(f, AutoEnzyme(), [1.0])
     catch e
-        buf = IOBuffer()
-        showerror(buf, e)
-        String(take!(buf))
     end
+    msg = sprint(showerror, e)
     @test occursin("AutoEnzyme", msg)
     @test occursin("function_annotation", msg)
     @test occursin("ADTypes", msg)
@@ -34,7 +33,8 @@ end
         return [g(active_var, constant_var, cond), g(active_var, constant_var, cond)]
     end
 
-    msg = try
+    e = nothing
+    try
         pushforward(
             h,
             AutoEnzyme(; mode=Enzyme.Forward),
@@ -44,10 +44,8 @@ end
             Constant(true),
         )
     catch e
-        buf = IOBuffer()
-        showerror(buf, e)
-        String(take!(buf))
     end
+    msg = sprint(showerror, e)
     @test occursin("AutoEnzyme", msg)
     @test occursin("mode", msg)
     @test occursin("set_runtime_activity", msg)
diff --git a/DifferentiationInterface/test/Core/Internals/hints.jl b/DifferentiationInterface/test/Core/Internals/hints.jl
index 754782730..83f43edaa 100644
--- a/DifferentiationInterface/test/Core/Internals/hints.jl
+++ b/DifferentiationInterface/test/Core/Internals/hints.jl
@@ -4,12 +4,11 @@ import DifferentiationInterface as DI
 using Test
 
 @testset "Missing backend" begin
-    msg = try
+    e = nothing
+    try
         gradient(sum, AutoZygote(), [1.0])
     catch e
-        buf = IOBuffer()
-        showerror(buf, e)
-        String(take!(buf))
     end
+    msg = sprint(showerror, e)
     @test occursin("import Zygote", msg)
 end

From d10ab87b85a0ec789efb23e902cb865fe33b37aa Mon Sep 17 00:00:00 2001
From: Guillaume Dalle <22795598+gdalle@users.noreply.github.com>
Date: Sat, 10 May 2025 07:35:04 +0200
Subject: [PATCH 5/6] Unreleased

---
 DifferentiationInterface/CHANGELOG.md | 2 --
 1 file changed, 2 deletions(-)

diff --git a/DifferentiationInterface/CHANGELOG.md b/DifferentiationInterface/CHANGELOG.md
index 9ec766c29..248a1ff8a 100644
--- a/DifferentiationInterface/CHANGELOG.md
+++ b/DifferentiationInterface/CHANGELOG.md
@@ -7,8 +7,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-## [0.6.54] - 2025-05-07
-
 ### Added
 
 - Error hints for Enzyme ([#788])

From 20e8be795101b6f036725c2f4163fe4d70f575af Mon Sep 17 00:00:00 2001
From: Guillaume Dalle <22795598+gdalle@users.noreply.github.com>
Date: Sat, 10 May 2025 08:17:50 +0200
Subject: [PATCH 6/6] Move

---
 .../test/Back/Enzyme/hints.jl                 | 54 -------------------
 .../test/Back/Enzyme/test.jl                  | 53 ++++++++++++++++++
 2 files changed, 53 insertions(+), 54 deletions(-)
 delete mode 100644 DifferentiationInterface/test/Back/Enzyme/hints.jl

diff --git a/DifferentiationInterface/test/Back/Enzyme/hints.jl b/DifferentiationInterface/test/Back/Enzyme/hints.jl
deleted file mode 100644
index 5a11c6b07..000000000
--- a/DifferentiationInterface/test/Back/Enzyme/hints.jl
+++ /dev/null
@@ -1,54 +0,0 @@
-using DifferentiationInterface
-using Enzyme: Enzyme
-using Test
-
-@testset "MutabilityError" begin
-    f = let
-        cache = [0.0]
-        x -> sum(copyto!(cache, x))
-    end
-
-    e = nothing
-    try
-        gradient(f, AutoEnzyme(), [1.0])
-    catch e
-    end
-    msg = sprint(showerror, e)
-    @test occursin("AutoEnzyme", msg)
-    @test occursin("function_annotation", msg)
-    @test occursin("ADTypes", msg)
-    @test occursin("DifferentiationInterface", msg)
-end
-
-@testset "RuntimeActivityError" begin
-    function g(active_var, constant_var, cond)
-        if cond
-            return active_var
-        else
-            return constant_var
-        end
-    end
-
-    function h(active_var, constant_var, cond)
-        return [g(active_var, constant_var, cond), g(active_var, constant_var, cond)]
-    end
-
-    e = nothing
-    try
-        pushforward(
-            h,
-            AutoEnzyme(; mode=Enzyme.Forward),
-            [1.0],
-            ([1.0],),
-            Constant([1.0]),
-            Constant(true),
-        )
-    catch e
-    end
-    msg = sprint(showerror, e)
-    @test occursin("AutoEnzyme", msg)
-    @test occursin("mode", msg)
-    @test occursin("set_runtime_activity", msg)
-    @test occursin("ADTypes", msg)
-    @test occursin("DifferentiationInterface", msg)
-end
diff --git a/DifferentiationInterface/test/Back/Enzyme/test.jl b/DifferentiationInterface/test/Back/Enzyme/test.jl
index a772e48ba..7e1b02451 100644
--- a/DifferentiationInterface/test/Back/Enzyme/test.jl
+++ b/DifferentiationInterface/test/Back/Enzyme/test.jl
@@ -148,3 +148,56 @@ end
         f_nocontext, AutoEnzyme(; mode=Enzyme.Reverse), rand(10), ConstantOrCache(nothing)
     )
 end
+
+@testset "Hints" begin
+    @testset "MutabilityError" begin
+        f = let
+            cache = [0.0]
+            x -> sum(copyto!(cache, x))
+        end
+
+        e = nothing
+        try
+            gradient(f, AutoEnzyme(), [1.0])
+        catch e
+        end
+        msg = sprint(showerror, e)
+        @test occursin("AutoEnzyme", msg)
+        @test occursin("function_annotation", msg)
+        @test occursin("ADTypes", msg)
+        @test occursin("DifferentiationInterface", msg)
+    end
+
+    @testset "RuntimeActivityError" begin
+        function g(active_var, constant_var, cond)
+            if cond
+                return active_var
+            else
+                return constant_var
+            end
+        end
+
+        function h(active_var, constant_var, cond)
+            return [g(active_var, constant_var, cond), g(active_var, constant_var, cond)]
+        end
+
+        e = nothing
+        try
+            pushforward(
+                h,
+                AutoEnzyme(; mode=Enzyme.Forward),
+                [1.0],
+                ([1.0],),
+                Constant([1.0]),
+                Constant(true),
+            )
+        catch e
+        end
+        msg = sprint(showerror, e)
+        @test occursin("AutoEnzyme", msg)
+        @test occursin("mode", msg)
+        @test occursin("set_runtime_activity", msg)
+        @test occursin("ADTypes", msg)
+        @test occursin("DifferentiationInterface", msg)
+    end
+end