Improve n-dimensional slicing of BlockIndexRange (#463)

Fixes #355. This is also fixed as a part of #462 but this PR is narrower
in scope so could be merged more quickly.

---------

Co-authored-by: Sheehan Olver <[email protected]>

Author: mtfishman

Project.toml

@@ -2,6 +2,7 @@ name = "BlockArrays"
 uuid = "8e7c35d0-a365-5155-bbbb-fb81a777f24e"
 version = "1.7.0"
 
+
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
 BandedMatrices = "aae01518-5342-5314-be14-df237901396f"

src/blockindices.jl

@@ -211,7 +211,8 @@ getindex(B::Block{N}, inds::Vararg{AbstractUnitRange{<:Integer},N}) where N = Bl
 getindex(B::Block{1}, inds::Colon) = B
 getindex(B::Block{1}, inds::Base.Slice) = B
 
-@propagate_inbounds getindex(B::BlockIndexRange{1}, kr::AbstractUnitRange{<:Integer}) = BlockIndexRange(B.block, B.indices[1][kr])
+getindex(B::BlockIndexRange{0}) = B.block[]
+@propagate_inbounds getindex(B::BlockIndexRange{N}, kr::Vararg{AbstractUnitRange{<:Integer},N}) where {N} = BlockIndexRange(B.block, map(getindex, B.indices, kr))
 @propagate_inbounds getindex(B::BlockIndexRange{N}, inds::Vararg{Int,N}) where N = B.block[Base.reindex(B.indices, inds)...]
 
 eltype(R::BlockIndexRange) = eltype(typeof(R))

test/test_blockindices.jl

@@ -90,6 +90,8 @@ import BlockArrays: BlockIndex, BlockIndexRange, BlockSlice, BlockedSlice
         @test Block(1,1)[1,1] == BlockIndex((1,1),(1,1)) == BlockIndex((1,1),(1,))
         @test Block(1,1)[1:2,1:2] == BlockIndexRange(Block(1,1),(1:2,1:2))
         @test Block(1)[1:3][1:2] == BlockIndexRange(Block(1),1:2)
+        @test Block(1,1)[2:4,2:4][2:3,2:3] == BlockIndexRange(Block(1,1),(3:4,3:4))
+        @test BlockIndexRange(Block(),())[] == BlockIndex()
         @test BlockIndex((2,2,2),(2,)) == BlockIndex((2,2,2),(2,1,)) == BlockIndex((2,2,2),(2,1,1))
         @test BlockIndex(2,(2,)) === BlockIndex((2,),(2,))
         @test BlockIndex(UInt(2),(2,)) === BlockIndex((UInt(2),),(2,))