Support unsafe_wrap on arrays of symbols (#2753)

Author: vchuravy

src/array.jl

@@ -24,7 +24,7 @@ function explain_eltype(@nospecialize(T), depth=0; maxdepth=10)
           msg *= explain_eltype(U, depth+1)
         end
       end
-    elseif Base.ismutabletype(T)
+    elseif Base.ismutabletype(T) && Base.datatype_fieldcount(T) != 0
       msg = "  "^depth * "$T is a mutable type\n"
     elseif hasfieldcount(T)
       msg = "  "^depth * "$T is a struct that's not allocated inline\n"
@@ -47,9 +47,22 @@ end
 #    these are stored with a selector at the end (handled by Julia).
 # 3. bitstype unions (`Union{Int, Float32}`, etc)
 #    these are stored contiguously and require a selector array (handled by us)
-@inline function check_eltype(name, T)
-  eltype_is_invalid = !Base.allocatedinline(T) || (hasfieldcount(T) && any(!Base.allocatedinline, fieldtypes(T)))
-  if eltype_is_invalid 
+# As well as "mutable singleton" types like `Symbol` that use pointer-identity
+
+function valid_type(@nospecialize(T))
+  if Base.allocatedinline(T)
+    if hasfieldcount(T)
+      return all(valid_type, fieldtypes(T))
+    end
+    return true
+  elseif Base.ismutabletype(T)
+    return Base.datatype_fieldcount(T) == 0
+  end
+  return false
+end
+
+@inline function check_eltype(name, T)                      
+  if !valid_type(T) 
     explanation = explain_eltype(T)
     error("""
       $name only supports element types that are allocated inline.
@@ -234,7 +247,7 @@ end
 function Base.unsafe_wrap(::Type{CuArray{T,N,M}},
                           ptr::CuPtr{T}, dims::NTuple{N,Int};
                           own::Bool=false, ctx::CuContext=context()) where {T,N,M}
-  isbitstype(T) || throw(ArgumentError("Can only unsafe_wrap a pointer to a bits type"))
+  check_eltype("unsafe_wrap(CuArray, ...)", T)
   sz = prod(dims) * aligned_sizeof(T)
 
   # create a memory object

test/base/array.jl

@@ -173,6 +173,18 @@ end
         cpu_arr = unsafe_wrap(Array, cpu_ptr, 1)
         @test cpu_arr == [42]
     end
+
+    # symbols and tuples thereof
+    let a = CuArray([:a])
+      b = unsafe_wrap(CuArray, pointer(a), 1)
+      @test typeof(b) <: CuArray{Symbol,1}
+      @test size(b) == (1,)
+    end
+    let a = CuArray([(:a,:b)])
+      b = unsafe_wrap(CuArray, pointer(a), 1)
+      @test typeof(b) <: CuArray{Tuple{Symbol,Symbol},1}
+      @test size(b) == (1,)
+    end
 end
 
 @testset "adapt" begin