From 5b893dd60c895ab4e2d5be0ff6781a20e7c5ad74 Mon Sep 17 00:00:00 2001
From: Keno Fischer <keno@juliacomputing.com>
Date: Thu, 27 Jan 2022 07:10:44 -0500
Subject: [PATCH] deleteat!: Handle unassigned array elements (#43941)

This function was erroring on unassigned array elements. This is
the minimal fix to resolve that issue. I tried something more
generic, but it turns out all of our Array code basically assumes
that all elements are assigned. Even basic things like `==`, `hash`,
etc. error for arrays with unassigned elements. I think we may want
to strongly consider removing the ability to unassign elements in
arrays in favor of Union{Nothing, T} arrays, which our existing code
handles fine and should be able to be made to have equivalent performance.
---
 base/array.jl    | 27 ++++++++++++++++++++++-----
 test/arrayops.jl |  5 +++++
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/base/array.jl b/base/array.jl
index 2fc1ccfdf7dda..807f99342e25f 100644
--- a/base/array.jl
+++ b/base/array.jl
@@ -1531,6 +1531,23 @@ deleteat!(a::Vector, inds::AbstractVector) = _deleteat!(a, to_indices(a, (inds,)
 
 struct Nowhere; end
 push!(::Nowhere, _) = nothing
+_growend!(::Nowhere, _) = nothing
+
+@inline function _push_deleted!(dltd, a::Vector, ind)
+    if @inbounds isassigned(a, ind)
+        push!(dltd, @inbounds a[ind])
+    else
+        _growend!(dltd, 1)
+    end
+end
+
+@inline function _copy_item!(a::Vector, p, q)
+    if @inbounds isassigned(a, q)
+        @inbounds a[p] = a[q]
+    else
+        _unsetindex!(a, p)
+    end
+end
 
 function _deleteat!(a::Vector, inds, dltd=Nowhere())
     n = length(a)
@@ -1538,7 +1555,7 @@ function _deleteat!(a::Vector, inds, dltd=Nowhere())
     y === nothing && return a
     (p, s) = y
     checkbounds(a, p)
-    push!(dltd, @inbounds a[p])
+    _push_deleted!(dltd, a, p)
     q = p+1
     while true
         y = iterate(inds, s)
@@ -1552,14 +1569,14 @@ function _deleteat!(a::Vector, inds, dltd=Nowhere())
             end
         end
         while q < i
-            @inbounds a[p] = a[q]
+            _copy_item!(a, p, q)
             p += 1; q += 1
         end
-        push!(dltd, @inbounds a[i])
+        _push_deleted!(dltd, a, i)
         q = i+1
     end
     while q <= n
-        @inbounds a[p] = a[q]
+        _copy_item!(a, p, q)
         p += 1; q += 1
     end
     _deleteend!(a, n-p+1)
@@ -1572,7 +1589,7 @@ function deleteat!(a::Vector, inds::AbstractVector{Bool})
     length(inds) == n || throw(BoundsError(a, inds))
     p = 1
     for (q, i) in enumerate(inds)
-        @inbounds a[p] = a[q]
+        _copy_item!(a, p, q)
         p += !i
     end
     _deleteend!(a, n-p+1)
diff --git a/test/arrayops.jl b/test/arrayops.jl
index 1cb8d667bef36..84b0e7d259f45 100644
--- a/test/arrayops.jl
+++ b/test/arrayops.jl
@@ -1516,6 +1516,11 @@ end
     @test_throws BoundsError deleteat!([], [2])
     @test deleteat!([], []) == []
     @test deleteat!([], Bool[]) == []
+    let a = Vector{Any}(undef, 2)
+        a[1] = 1
+        @test isassigned(deleteat!(copy(a), [2]), 1)
+        @test !isassigned(deleteat!(copy(a), [1]), 1)
+    end
 end
 
 @testset "comprehensions" begin