Un-deprecate setindex with multidimensional indices

Back in #10525, I decided to deprecate `setindex!(A, x, I::Union{Real, Int, AbstractArray}...)` for symmetry since `getindex` only allows vector indices when there's more than one index.

But looking forward, I would really like to work towards APL semantics in 0.5 wherein the sum of the dimensionality of the indices is the dimensionality of the output array.  For example, indexing `A[[1 2; 3 4], 1]` would output a 2-dimensional `2x2` array: `[A[1,1] A[2, 1]; A[3,1] A[4,1]]`.  In which case, we'd add support back in for `setindex!` with array indices for symmetry.  This seems like needless churn - let's just leave things be until 0.5.

base/deprecated.jl

@@ -507,15 +507,6 @@ function chol(A::AbstractMatrix, uplo::Symbol)
     chol(A, Val{uplo})
 end
 
-_ensure_vector(A::AbstractArray) = vec(A)
-_ensure_vector(A) = A
-_ensure_vectors() = ()
-_ensure_vectors(A, As...) = (_ensure_vector(A), _ensure_vectors(As...)...)
-function _unsafe_setindex!(l::LinearIndexing, A::AbstractArray, x, J::Union{Real,AbstractArray,Colon}...)
-    depwarn("multidimensional indexed assignment with multidimensional arrays is deprecated, use vec to convert indices to vectors", :_unsafe_setindex!)
-    _unsafe_setindex!(l, A, x, _ensure_vectors(J...)...)
-end
-
 # 11554
 
 read!(from::AbstractIOBuffer, p::Ptr, nb::Integer) = read!(from, p, Int(nb))

base/multidimensional.jl

@@ -161,8 +161,8 @@ index_lengths_dim(A, dim) = ()
 index_lengths_dim(A, dim, ::Colon) = (trailingsize(A, dim),)
 @inline index_lengths_dim(A, dim, ::Colon, i, I...) = (size(A, dim), index_lengths_dim(A, dim+1, i, I...)...)
 @inline index_lengths_dim(A, dim, ::Real, I...) = (1, index_lengths_dim(A, dim+1, I...)...)
-@inline index_lengths_dim(A, dim, i::AbstractVector{Bool}, I...) = (sum(i), index_lengths_dim(A, dim+1, I...)...)
-@inline index_lengths_dim(A, dim, i::AbstractVector, I...) = (length(i), index_lengths_dim(A, dim+1, I...)...)
+@inline index_lengths_dim(A, dim, i::AbstractArray{Bool}, I...) = (sum(i), index_lengths_dim(A, dim+1, I...)...)
+@inline index_lengths_dim(A, dim, i::AbstractArray, I...) = (length(i), index_lengths_dim(A, dim+1, I...)...)
 
 # shape of array to create for getindex() with indexes I, dropping trailing scalars
 index_shape(A::AbstractArray, I::AbstractArray) = size(I) # Linear index reshape
@@ -290,15 +290,12 @@ _iterable(v) = repeated(v)
     checkbounds(A, J...)
     _unsafe_setindex!(l, A, x, J...)
 end
-@inline function _unsafe_setindex!(l::LinearIndexing, A::AbstractArray, x, J::Union{Real,AbstractVector,Colon}...)
+@inline function _unsafe_setindex!(l::LinearIndexing, A::AbstractArray, x, J::Union{Real,AbstractArray,Colon}...)
     _unsafe_batchsetindex!(l, A, _iterable(x), to_indexes(J...)...)
 end
 
-# While setindex! with one array argument doesn't mean anything special, it is
-# still supported for symmetry with getindex.
-_unsafe_setindex!(l::LinearIndexing, A::AbstractArray, x, I::AbstractArray) = _unsafe_setindex!(l, A, x, vec(I))
 # 1-d logical indexing: override the above to avoid calling find (in to_index)
-function _unsafe_setindex!(::LinearIndexing, A::AbstractArray, x, I::AbstractVector{Bool})
+function _unsafe_setindex!(::LinearIndexing, A::AbstractArray, x, I::AbstractArray{Bool})
     X = _iterable(x)
     Xs = start(X)
     i = 0
@@ -317,7 +314,7 @@ function _unsafe_setindex!(::LinearIndexing, A::AbstractArray, x, I::AbstractVec
 end
 
 # Use iteration over X so we don't need to worry about its storage
-@generated function _unsafe_batchsetindex!(::LinearFast, A::AbstractArray, X, I::Union{Real,AbstractVector,Colon}...)
+@generated function _unsafe_batchsetindex!(::LinearFast, A::AbstractArray, X, I::Union{Real,AbstractArray,Colon}...)
     N = length(I)
     quote
         @nexprs $N d->(I_d = I[d])
@@ -334,7 +331,7 @@ end
         A
     end
 end
-@generated function _unsafe_batchsetindex!(::LinearSlow, A::AbstractArray, X, I::Union{Real,AbstractVector,Colon}...)
+@generated function _unsafe_batchsetindex!(::LinearSlow, A::AbstractArray, X, I::Union{Real,AbstractArray,Colon}...)
     N = length(I)
     quote
         @nexprs $N d->(I_d = I[d])

test/arrayops.jl

@@ -40,6 +40,14 @@ a[2,2] = 4
 b = a'
 @test a[1,1] == 1. && a[1,2] == 2. && a[2,1] == 3. && a[2,2] == 4.
 @test b[1,1] == 1. && b[2,1] == 2. && b[1,2] == 3. && b[2,2] == 4.
+a[[1 2 3 4]] = 0
+@test a == zeros(2,2)
+a[[1 2], [1 2]] = 1
+@test a == ones(2,2)
+a[[1 2], 1] = 0
+@test a[1,1] == 0. && a[1,2] == 1. && a[2,1] == 0. && a[2,2] == 1.
+a[:, [1 2]] = 2
+@test a == 2ones(2,2)
 
 a = Array(Float64, 2, 2, 2, 2, 2)
 a[1,1,1,1,1] = 10