Don't sort inplace in sortedunion (#381)

* don't sort inplace in sortedunion

* Tests for maybeinplacesort

src/blockbroadcast.jl

@@ -29,7 +29,9 @@ BroadcastStyle(::PseudoBlockStyle{M}, ::BlockStyle{N}) where {M,N} = BlockStyle(
 
 
 # sortedunion can assume inputs are already sorted so this could be improved
-sortedunion(a,b) = sort!(union(a,b))
+maybeinplacesort!(v::StridedVector) = sort!(v)
+maybeinplacesort!(v) = sort(v)
+sortedunion(a,b) = maybeinplacesort!(union(a,b))
 sortedunion(a::Base.OneTo, b::Base.OneTo) = Base.OneTo(max(last(a),last(b)))
 sortedunion(a::AbstractUnitRange, b::AbstractUnitRange) = min(first(a),first(b)):max(last(a),last(b))
 combine_blockaxes(a, b) = _BlockedUnitRange(sortedunion(blocklasts(a), blocklasts(b)))

test/test_blockbroadcast.jl

@@ -278,4 +278,16 @@ import BlockArrays: SubBlockIterator, BlockIndexRange, Diagonal
         C = B + B
         @test C[Block(1)] == 2B[Block(1)]
     end
+
+    @testset "utilities" begin
+        for v in ([2,3,1], 2:4)
+            w = BlockArrays.maybeinplacesort!(v)
+            @test issorted(w)
+            @test v === w
+        end
+        v = 3:-1:2
+        w = BlockArrays.maybeinplacesort!(v)
+        @test issorted(w)
+        @test w == reverse(v)
+    end
 end