fix half of #125

Author: mcabbott

src/lib/array.jl

@@ -171,7 +171,9 @@ end
 
 for i = 0:2, c = combinations([:AbstractArray, :TrackedArray, :Number], i), f = [:hcat, :vcat]
   cnames = map(_ -> gensym(), c)
-  @eval Base.$f($([:($x::$c) for (x, c) in zip(cnames, c)]...), x::Union{TrackedArray,TrackedReal}, xs::Union{AbstractArray,Number}...) =
+  @eval Base.$f($([:($x::$c) for (x, c) in zip(cnames, c)]...), x::Union{TrackedArray,TrackedReal}, xs::AbstractArray...) =
+    track($f, $(cnames...), x, xs...)
+  @eval Base.$f($([:($x::$c) for (x, c) in zip(cnames, c)]...), x::Union{TrackedArray,TrackedReal}, xs::Number...) =
     track($f, $(cnames...), x, xs...)
 end
 

test/tracker.jl

@@ -129,9 +129,11 @@ end
 
   @testset "scalars" begin
     @test vcat(param([1, 2, 3]), 1) isa TrackedArray
+    @test vcat(param(1), 2) isa TrackedArray
+
+    # These two are ambiguity errors on Julia 1.8
     @test vcat(1, param([1, 2, 3])) isa TrackedArray
     @test hcat(1, param([1 2 3;])) isa TrackedArray
-    @test vcat(param(1), 2) isa TrackedArray
   end
 
 end