From 009dce884f5b971f5c8b3e81457d175d85e5a9a2 Mon Sep 17 00:00:00 2001
From: David Widmann <devmotion@users.noreply.github.com>
Date: Mon, 7 Apr 2025 22:46:36 +0200
Subject: [PATCH] Fix seeding with undefined elements

---
 src/apiutils.jl      | 56 +++++++++++++++++++++++++++++++++++++-------
 test/JacobianTest.jl | 14 +++++++++++
 2 files changed, 62 insertions(+), 8 deletions(-)

diff --git a/src/apiutils.jl b/src/apiutils.jl
index 39608d6c..f401a3fc 100644
--- a/src/apiutils.jl
+++ b/src/apiutils.jl
@@ -72,16 +72,36 @@ end
 
 function seed!(duals::AbstractArray{Dual{T,V,N}}, x,
                seed::Partials{N,V} = zero(Partials{N,V})) where {T,V,N}
-    for idx in structural_eachindex(duals, x)
-        duals[idx] = Dual{T,V,N}(x[idx], seed)
+    if isbitstype(V)
+        for idx in structural_eachindex(duals, x)
+            duals[idx] = Dual{T,V,N}(x[idx], seed)
+        end
+    else
+        for idx in structural_eachindex(duals, x)
+            if isassigned(x, idx)
+                duals[idx] = Dual{T,V,N}(x[idx], seed)
+            else
+                Base._unsetindex!(duals, idx)
+            end
+        end
     end
     return duals
 end
 
 function seed!(duals::AbstractArray{Dual{T,V,N}}, x,
                seeds::NTuple{N,Partials{N,V}}) where {T,V,N}
-    for (i, idx) in zip(1:N, structural_eachindex(duals, x))
-        duals[idx] = Dual{T,V,N}(x[idx], seeds[i])
+    if isbitstype(V)
+        for (i, idx) in zip(1:N, structural_eachindex(duals, x))
+            duals[idx] = Dual{T,V,N}(x[idx], seeds[i])
+        end
+    else
+        for (i, idx) in zip(1:N, structural_eachindex(duals, x))
+            if isassigned(x, idx)
+                duals[idx] = Dual{T,V,N}(x[idx], seeds[i])
+            else
+                Base._unsetindex!(duals, idx)
+            end
+        end
     end
     return duals
 end
@@ -90,8 +110,18 @@ function seed!(duals::AbstractArray{Dual{T,V,N}}, x, index,
                seed::Partials{N,V} = zero(Partials{N,V})) where {T,V,N}
     offset = index - 1
     idxs = Iterators.drop(structural_eachindex(duals, x), offset)
-    for idx in idxs
-        duals[idx] = Dual{T,V,N}(x[idx], seed)
+    if isbitstype(V)
+        for idx in idxs
+            duals[idx] = Dual{T,V,N}(x[idx], seed)
+        end
+    else
+        for idx in idxs
+            if isassigned(x, idx)
+                duals[idx] = Dual{T,V,N}(x[idx], seed)
+            else
+                Base._unsetindex!(duals, idx)
+            end
+        end
     end
     return duals
 end
@@ -100,8 +130,18 @@ function seed!(duals::AbstractArray{Dual{T,V,N}}, x, index,
                seeds::NTuple{N,Partials{N,V}}, chunksize = N) where {T,V,N}
     offset = index - 1
     idxs = Iterators.drop(structural_eachindex(duals, x), offset)
-    for (i, idx) in zip(1:chunksize, idxs)
-        duals[idx] = Dual{T,V,N}(x[idx], seeds[i])
+    if isbitstype(V)
+        for (i, idx) in zip(1:chunksize, idxs)
+            duals[idx] = Dual{T,V,N}(x[idx], seeds[i])
+        end
+    else
+        for (i, idx) in zip(1:chunksize, idxs)
+            if isassigned(x, idx)
+                duals[idx] = Dual{T,V,N}(x[idx], seeds[i])
+            else
+                Base._unsetindex!(duals, idx)
+            end
+        end
     end
     return duals
 end
diff --git a/test/JacobianTest.jl b/test/JacobianTest.jl
index 1e52f7fa..76fa93ed 100644
--- a/test/JacobianTest.jl
+++ b/test/JacobianTest.jl
@@ -279,4 +279,18 @@ end
     end
 end
 
+@testset "BigFloat" begin
+    # issues #436, #740
+    for n in (2, 20)
+        x = BigFloat.(1:n)
+        @test x isa Vector{BigFloat}
+        y = similar(x)
+        @test !isassigned(y, 1)
+        res = ForwardDiff.jacobian(copyto!, y, x)
+        @test y == x
+        @test res isa Matrix{BigFloat}
+        @test res == I
+    end
+end
+
 end # module