fix #6466, deprecate write on non-isbits arrays

Also remove an unnecessary method, and generalize a `write` method
for `SubArray` from `::IOStream` to `::IO`.

NEWS.md

@@ -221,6 +221,9 @@ Deprecated or removed
   * The function `showall` is deprecated. Showing entire values is the default, unless an
     `IOContext` specifying `:limit=>true` is in use ([#22847]).
 
+  * Calling `write` on non-isbits arrays is deprecated in favor of explicit loops or
+    `serialize` ([#6466]).
+
 
 Julia v0.6.0 Release Notes
 ==========================

base/deprecated.jl

@@ -1591,6 +1591,9 @@ end
 @deprecate readstring(filename::AbstractString) read(filename, String)
 @deprecate readstring(cmd::AbstractCmd) read(cmd, String)
 
+# issue #6466
+# `write` on non-isbits arrays is deprecated in io.jl.
+
 # END 0.7 deprecations
 
 # BEGIN 1.0 deprecations

base/io.jl

@@ -314,21 +314,21 @@ write(s::IO, x::Bool) = write(s, UInt8(x))
 write(to::IO, p::Ptr) = write(to, convert(UInt, p))
 
 function write(s::IO, A::AbstractArray)
+    if !isbits(eltype(A))
+        depwarn("Calling `write` on non-isbits arrays is deprecated. Use a loop or `serialize` instead.", :write)
+    end
     nb = 0
     for a in A
         nb += write(s, a)
     end
     return nb
 end
 
-@noinline function write(s::IO, a::Array{UInt8}) # mark noinline to ensure the array is gc-rooted somewhere (by the caller)
-    return unsafe_write(s, pointer(a), sizeof(a))
-end
-
-@noinline function write(s::IO, a::Array{T}) where T # mark noinline to ensure the array is gc-rooted somewhere (by the caller)
-    if isbits(T)
+@noinline function write(s::IO, a::Array)  # mark noinline to ensure the array is gc-rooted somewhere (by the caller)
+    if isbits(eltype(a))
         return unsafe_write(s, pointer(a), sizeof(a))
     else
+        depwarn("Calling `write` on non-isbits arrays is deprecated. Use a loop or `serialize` instead.", :write)
         nb = 0
         for b in a
             nb += write(s, b)
@@ -337,6 +337,27 @@ end
     end
 end
 
+function write(s::IO, a::SubArray{T,N,<:Array}) where {T,N}
+    if !isbits(T)
+        return invoke(write, Tuple{IO, AbstractArray}, s, a)
+    end
+    elsz = sizeof(T)
+    colsz = size(a,1) * elsz
+    if stride(a,1) != 1
+        for idxs in CartesianRange(size(a))
+            unsafe_write(s, pointer(a, idxs.I), elsz)
+        end
+        return elsz * length(a)
+    elseif N <= 1
+        return unsafe_write(s, pointer(a, 1), colsz)
+    else
+        for idxs in CartesianRange((1, size(a)[2:end]...))
+            unsafe_write(s, pointer(a, idxs.I), colsz)
+        end
+        return colsz * trailingsize(a,2)
+    end
+end
+
 
 function write(s::IO, ch::Char)
     c = reinterpret(UInt32, ch)

base/iostream.jl

@@ -169,21 +169,6 @@ function unsafe_write(s::IOStream, p::Ptr{UInt8}, nb::UInt)
     return Int(ccall(:ios_write, Csize_t, (Ptr{Void}, Ptr{Void}, Csize_t), s.ios, p, nb))
 end
 
-function write(s::IOStream, a::SubArray{T,N,<:Array}) where {T,N}
-    if !isbits(T) || stride(a,1)!=1
-        return invoke(write, Tuple{Any, AbstractArray}, s, a)
-    end
-    colsz = size(a,1)*sizeof(T)
-    if N<=1
-        return unsafe_write(s, pointer(a, 1), colsz)
-    else
-        for idxs in CartesianRange((1, size(a)[2:end]...))
-            unsafe_write(s, pointer(a, idxs.I), colsz)
-        end
-        return colsz*trailingsize(a,2)
-    end
-end
-
 # num bytes available without blocking
 nb_available(s::IOStream) = ccall(:jl_nb_available, Int32, (Ptr{Void},), s.ios)