make cat(As..., dims=Val((1,2,...)) work (#44211)

Author: thchr

base/abstractarray.jl

@@ -1712,13 +1712,15 @@ end
 _cs(d, a, b) = (a == b ? a : throw(DimensionMismatch(
     "mismatch in dimension $d (expected $a got $b)")))
 
-function dims2cat(::Val{n}) where {n}
-    n <= 0 && throw(ArgumentError("cat dimension must be a positive integer, but got $n"))
-    ntuple(i -> (i == n), Val(n))
+function dims2cat(::Val{dims}) where dims
+    if any(≤(0), dims)
+        throw(ArgumentError("All cat dimensions must be positive integers, but got $dims"))
+    end
+    ntuple(in(dims), maximum(dims))
 end
 
 function dims2cat(dims)
-    if any(dims .<= 0)
+    if any(≤(0), dims)
         throw(ArgumentError("All cat dimensions must be positive integers, but got $dims"))
     end
     ntuple(in(dims), maximum(dims))

test/abstractarray.jl

@@ -732,6 +732,7 @@ function test_cat(::Type{TestAbstractArray})
     @test @inferred(cat(As...; dims=Val(3))) == zeros(2, 2, 2)
     cat3v(As) = cat(As...; dims=Val(3))
     @test @inferred(cat3v(As)) == zeros(2, 2, 2)
+    @test @inferred(cat(As...; dims=Val((1,2)))) == zeros(4, 4)
 end
 
 function test_ind2sub(::Type{TestAbstractArray})