Add FastBroadcast alloc test

Add broken test

test/Fields/field_opt.jl

@@ -7,6 +7,7 @@ import ClimaCore.DataLayouts: IJFH
 import ClimaCore:
     Fields, slab, Domains, Topologies, Meshes, Operators, Spaces, Geometry
 
+using FastBroadcast
 using LinearAlgebra: norm
 using Statistics: mean
 using ForwardDiff
@@ -71,6 +72,33 @@ end
     end
 end
 
+function fast_broadcast_single_field!(Y1, dt, Y2)
+    x = Y1.x
+    @.. x += 2.0
+    nothing
+end
+# Removing dt from argument fixes allocations
+function fast_broadcast_copyto!(Y1, dt, Y2)
+    @.. Y1 = Y2
+    nothing
+end
+# https://github.com/CliMA/ClimaCore.jl/issues/1356
+@testset "Allocations in @.. broadcasting" begin
+    FT = Float32
+    for space in TU.all_spaces(FT)
+        Y1 = fill((; x = FT(2.0), y = FT(2.0), z = FT(2.0)), space)
+        Y2 = fill((; x = FT(2.0), y = FT(2.0), z = FT(2.0)), space)
+        Y3 = fill((; x = FT(2.0), y = FT(2.0), z = FT(2.0)), space)
+        dt = FT(2.0)
+        fast_broadcast_single_field!(Y1, dt, Y2)
+        p = @allocated fast_broadcast_single_field!(Y1, dt, Y2)
+        @test p == 0
+        fast_broadcast_copyto!(Y1, dt, Y2)
+        p = @allocated fast_broadcast_copyto!(Y1, dt, Y2)
+        @test_broken p == 0
+    end
+end
+
 # https://github.com/CliMA/ClimaCore.jl/issues/963
 sc(::Type{FT}) where {FT} =
     Operators.StencilCoefs{-1, 1}((zero(FT), one(FT), zero(FT)))

test/Project.toml

@@ -10,6 +10,7 @@ ClimaCore = "d414da3d-4745-48bb-8d80-42e94e092884"
 Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 CubedSphere = "7445602f-e544-4518-8976-18f8e8ae6cdb"
 DiffEqBase = "2b5f629d-d688-5b77-993f-72d75c75574e"
+FastBroadcast = "7034ab61-46d4-4ed7-9d0f-46aef9175898"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 GFlops = "2ea8233c-34d4-5acc-88b4-02f326385bcc"
 GaussQuadrature = "d54b0c1a-921d-58e0-8e36-89d8069c0969"