Backends are adaptors (#364)

Author: vchuravy

.buildkite/pipeline.yml

@@ -6,8 +6,6 @@ steps:
           - "1.6"
           - "1.7"
           - "1.8"
-        cuda:
-          - "vc/ka_transition"
     env:
       KERNELABSTRACTIONS_TEST_BACKEND: "CUDA"
     plugins:
@@ -19,10 +17,10 @@ steps:
             - src
     commands: 
       - |
-        julia -e 'using Pkg
+        julia --project=test/projects/cuda -e 'using Pkg
                 println("--- :julia: Instantiating project")
+                Pkg.instantiate()
                 Pkg.develop(; path=pwd())
-                Pkg.add(; name="CUDA", rev="{{matrix.cuda}}")
                 println("+++ :julia: Running tests")
                 Pkg.test("CUDA"; coverage=true, test_args=["kernelabstractions"])'
     agents:

src/KernelAbstractions.jl

@@ -360,6 +360,11 @@ get_backend(A::Tridiagonal) = get_backend(A.d)
 
 get_backend(::Array) = CPU()
 
+# Define:
+#   adapt_storage(::Backend, a::Array) = adapt(BackendArray, a)
+#   adapt_storage(::Backend, a::BackendArray) = a
+Adapt.adapt_storage(::CPU, a::Array) = a
+
 """
     allocate(::Backend, Type, dims...)
 

test/Project.toml

@@ -1,4 +1,5 @@
 [deps]
+Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"