better h/vcat, fixes #378

src/tracker/lib/array.jl

@@ -136,30 +136,30 @@ Base.repeat(xs::TrackedArray; kw...) = track(repeat, xs; kw...)
   end
 end
 
-for f in [:vcat, :hcat]
-  UArray = :(Union{TrackedArray,Vector,Matrix,Adjoint,Transpose})
-  @eval begin
-    # This section is a bit of a hack since julia doesn't have a standardised
-    # promotion mechanism for concatenation yet
-    # https://github.com/JuliaLang/julia/pull/20815
+function combinations(xs, n)
+  n < 1 && return [[]]
+  cs = combinations(xs, n-1)
+  [[x, c...] for x in xs, c in cs]
+end
 
-    # It should support tracked concatenation with rank ∈ (1,2) with a
-    # TrackedArray anywhere among the arguments This works as long as base has
-    # other functions that captures `(::Union{Vector,RowVector,Matrix}...)`.
-    Base.$f(a::$UArray...) = track($f, a...)
+combinations([AbstractArray, TrackedArray], 2)
 
-    # It should support tracked concatenation with rank>2 if the TrackedArray is
-    # first
-    Base.$f(a::TrackedArray, b::AbstractArray...) = track($f, a, b...)
-    Base.$f(a::TrackedArray, b::$UArray...) = track($f, a, b...) # resolves ambiguity introduced by previous row
+for i = 0:2, c = combinations([:AbstractArray, :TrackedArray], i), f = [:hcat, :vcat]
+  cnames = map(_ -> gensym(), c)
+  @eval Base.$f($([:($x::$c) for (x, c) in zip(cnames, c)]...), x::TrackedArray, xs::AbstractArray...) =
+    track($f, $(cnames...), x, xs...)
+end
 
-    # It should support tracked concatenation with rank>2 if the TrackedArray is
-    # second
-    Base.$f(a::Array, b::TrackedArray, c::AbstractArray...) = track($f, a, b, c...)
-    Base.$f(a::Union{Vector,Matrix,Adjoint,Transpose}, b::TrackedArray,
-            c::$UArray...) =
-      track($f, a, b, c...) # resolves ambiguity introduced by previous row
-  end
+for i = 0:2, c = combinations([:AbstractVecOrMat, :TrackedVecOrMat], i), f = [:hcat, :vcat]
+  cnames = map(_ -> gensym(), c)
+  @eval Base.$f($([:($x::$c{T}) for (x, c) in zip(cnames, c)]...), x::TrackedVecOrMat{T}, xs::AbstractVecOrMat{T}...) where T =
+    track($f, $(cnames...), x, xs...)
+end
+
+for i = 0:2, c = combinations([:AbstractVector, :TrackedVector], i), f = [:hcat, :vcat]
+  cnames = map(_ -> gensym(), c)
+  @eval Base.$f($([:($x::$c{T}) for (x, c) in zip(cnames, c)]...), x::TrackedVector{T}, xs::AbstractVector{T}...) where T =
+    track($f, $(cnames...), x, xs...)
 end
 
 @grad function vcat(xs...)
@@ -192,10 +192,11 @@ end
   end
 end
 
-Base.cat(a::TrackedArray; dims) = track(cat, a, dims = dims)
-Base.cat(a::TrackedArray, b::TrackedArray, c::AbstractArray...; dims) = track(cat, a, b, c..., dims = dims)
-Base.cat(a::TrackedArray, b::AbstractArray, c::AbstractArray...; dims) = track(cat, a, b, c..., dims = dims)
-Base.cat(a::AbstractArray, b::TrackedArray, c::AbstractArray...; dims) = track(cat, a, b, c..., dims = dims)
+for i = 0:2, c = combinations([:AbstractArray, :TrackedArray], i)
+  cnames = map(_ -> gensym(), c)
+  @eval Base.cat($([:($x::$c) for (x, c) in zip(cnames, c)]...), x::TrackedArray, xs::AbstractArray...; dims) =
+    track(cat, $(cnames...), x, xs..., dims = dims)
+end
 
 @grad function cat(Xs...; dims)
   cat(data.(Xs)..., dims = dims), function (Δ)

test/tracker.jl

@@ -42,12 +42,7 @@ function promotiontest(f, A, B, C)
   r0 = f(A, B, C)
   r1 = f(param(A), B, C)
   r2 = f(A, param(B), C)
-  if all(ndims.((A,B,C)) .≤ 2) && f ∈ [hcat, vcat]
-    r3 = f(A, B, param(C))
-  else
-    @test_throws MethodError f(A, B, param(C)) # until julia#20815 is resolved
-    r3 = r2
-  end
+  r3 = f(A, B, param(C))
   r4 = f(param(A), param(B), param(C))
 
   @test !isa(r0, TrackedArray)