feat: define outer repeat method for TracedRArray (EnzymeAD#361)

* Add repeat method

* Add repeat tests

* Update test/basic.jl


* Update src/TracedRArray.jl

Author: AntonOresten

src/TracedRArray.jl

@@ -729,3 +729,27 @@ end
 
 Base.all(f::Function, x::AnyTracedRArray) = mapreduce(f, &, x)
 Base.any(f::Function, x::AnyTracedRArray) = mapreduce(f, |, x)
+
+# outer repeat
+function Base.repeat(x::AnyTracedRArray{T,N}, counts::Vararg{Int,M}) where {T,N,M}
+    P = max(N, M) # potentially padded
+
+    # (d1, d2, ..., dP) -> (d1, 1, d2, 1, ..., dP, 1)
+    interleaved_size = ones(Int, 2P)
+    interleaved_size[1:2:2N] .= size(x)
+
+    x_interleaved = reshape(x, interleaved_size...)
+
+    # (d1, 1, d2, 1, ..., dP, 1) -> (d1, r1, d2, r2, ..., dP, rP)
+    broadcast_target_size = interleaved_size
+    broadcast_target_size[2:2:2M] .= counts
+
+    x_broadcasted = broadcast_to_size(x_interleaved, broadcast_target_size)
+
+    # (d1, r1, d2, r2, ..., dP, rP) -> (d1*r1, d2*r2, ..., dP*rP)
+    final_size = vec(prod(reshape(broadcast_target_size, 2, :), dims=1))
+
+    x_final = reshape(x_broadcasted, final_size...)
+
+    return x_final
+end

test/basic.jl

@@ -364,6 +364,16 @@ end
     end
 end
 
+@testset "repeat" begin
+    @testset for (size, counts) in Iterators.product(
+        [(2,), (2,3), (2,3,4), (2,3,4,5)],
+        [(), (1,), (2,), (2,1), (1,2), (2,2), (2,2,2), (1,1,1,1,1)]
+    )
+        x = rand(size...)
+        @test (@jit repeat(Reactant.to_rarray(x), counts...)) == repeat(x, counts...)
+    end
+end
+
 function update_on_copy(x)
     y = x[1:2, 2:4, :]
     y[1:1, 1:1, :] = ones(1, 1, 3)