Fix broadcast_shape type instability

Author: charleskawczynski

Diff for: src/blockbroadcast.jl

@@ -34,9 +34,9 @@ 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)))
 
-Base.Broadcast.axistype(a::BlockedUnitRange, b::BlockedUnitRange) = length(b) == 1 ? a : combine_blockaxes(a, b)
-Base.Broadcast.axistype(a::BlockedUnitRange, b) = length(b) == 1 ? a : combine_blockaxes(a, b)
-Base.Broadcast.axistype(a, b::BlockedUnitRange) = length(b) == 1 ? a : combine_blockaxes(a, b)
+Base.Broadcast.axistype(a::BlockedUnitRange, b::BlockedUnitRange) = combine_blockaxes(a, b)
+Base.Broadcast.axistype(a::BlockedUnitRange, b) = combine_blockaxes(a, b)
+Base.Broadcast.axistype(a, b::BlockedUnitRange) = combine_blockaxes(a, b)
 
 
 similar(bc::Broadcasted{<:AbstractBlockStyle{N}}, ::Type{T}) where {T,N} =

Diff for: test/test_blockbroadcast.jl

@@ -182,6 +182,13 @@ import BlockArrays: SubBlockIterator, BlockIndexRange, Diagonal
         u = BlockArray(randn(5), [2,3]);
         @inferred(copyto!(similar(u), Base.broadcasted(exp, u)))
         @test exp.(u) == exp.(Vector(u))
+
+        shape1 = (BlockArrays._BlockedUnitRange((2,)),);
+        shape2 = (BlockArrays._BlockedUnitRange((2,)),);
+        @inferred Base.Broadcast.axistype(shape1[1], shape2[1])
+        @inferred BlockArrays.combine_blockaxes(shape1[1], shape2[1])
+        @inferred Base.Broadcast.broadcast_shape(shape1, shape2)
+        @code_warntype Base.Broadcast.broadcast_shape(shape1, shape2)
     end
 
     @testset "adjtrans" begin