RFC: make Ref(x) always construct a RefValue(x) object

NEWS.md

@@ -132,6 +132,8 @@ Language changes
   * Prefix `&` for by-reference arguments to `ccall` has been deprecated in favor of
     `Ref` argument types ([#6080]).
 
+  * The constructor `Ref(x::T)` now always returns a `Ref{T}` ([#21527]).
+
   * All line numbers in ASTs are represented by `LineNumberNode`s; the `:line` expression
     head is no longer used. `QuoteNode`s are also consistently used for quoted symbols instead
     of the `:quote` expression head (though `:quote` `Expr`s are still used for quoted

base/deprecated.jl

@@ -3423,6 +3423,11 @@ workspace() = error("workspace() is discontinued, check out Revise.jl for an alt
 # PR #25113
 @deprecate_binding CartesianRange CartesianIndices
 
+# PR 21527
+@deprecate Ref(x::AbstractArray) Ref(x, 1)
+@deprecate Ref(x::Ptr) Ref(x, 1)
+@deprecate Ref(x::Ref) x # or perhaps, `convert(Ref, x)`
+
 # END 0.7 deprecations
 
 # BEGIN 1.0 deprecations

base/libgit2/merge.jl

@@ -81,7 +81,7 @@ Return two outputs, `analysis` and `preference`. `analysis` has several possible
 function merge_analysis(repo::GitRepo, anns::Vector{GitAnnotated})
     analysis = Ref{Cint}(0)
     preference = Ref{Cint}(0)
-    anns_ref = Ref(map(a->a.ptr, anns))
+    anns_ref = Ref(map(a->a.ptr, anns), 1)
     anns_size = Csize_t(length(anns))
     @check ccall((:git_merge_analysis, :libgit2), Cint,
                   (Ptr{Cint}, Ptr{Cint}, Ptr{Void}, Ptr{Ptr{Void}}, Csize_t),

base/refpointer.jl

@@ -7,10 +7,16 @@ An object that safely references data of type `T`. This type is guaranteed to po
 valid, Julia-allocated memory of the correct type. The underlying data is protected from
 freeing by the garbage collector as long as the `Ref` itself is referenced.
 
+In Julia, `Ref` objects are dereferenced (loaded or stored) with `[]`.
+
+Creation of a `Ref` to a value `x` of type `T` is usually written `Ref(x)`.
+Additionally, for creating interior pointers to containers (such as Array or Ptr),
+it can be written `Ref(a, i)` for creating a reference to the `i`-th element of `a`.
+
 When passed as a `ccall` argument (either as a `Ptr` or `Ref` type), a `Ref` object will be
 converted to a native pointer to the data it references.
 
-There is no invalid (NULL) `Ref`.
+There is no invalid (NULL) `Ref` in Julia, but a `C_NULL` instance of `Ptr` can be passed to a `ccall` Ref argument.
 """
 Ref
 
@@ -44,14 +50,14 @@ end
 RefValue(x::T) where {T} = RefValue{T}(x)
 isassigned(x::RefValue) = isdefined(x, :x)
 
-Ref(x::Ref) = x
 Ref(x::Any) = RefValue(x)
-Ref(x::Ptr{T}, i::Integer=1) where {T} = x + (i-1)*Core.sizeof(T)
-Ref(x, i::Integer) = (i != 1 && error("Object only has one element"); Ref(x))
 Ref{T}() where {T} = RefValue{T}() # Ref{T}()
 Ref{T}(x) where {T} = RefValue{T}(x) # Ref{T}(x)
 convert(::Type{Ref{T}}, x) where {T} = RefValue{T}(x)
 
+Ref(x::Ref, i::Integer) = (i != 1 && error("Ref only has one element"); x)
+Ref(x::Ptr{T}, i::Integer) where {T} = x + (i - 1) * Core.sizeof(T)
+
 function unsafe_convert(P::Type{Ptr{T}}, b::RefValue{T}) where T
     if isbits(T) || isbitsunion(T)
         return convert(P, pointer_from_objref(b))
@@ -81,7 +87,7 @@ end
 RefArray(x::AbstractArray{T}, i::Int, roots::Any) where {T} = RefArray{T,typeof(x),Any}(x, i, roots)
 RefArray(x::AbstractArray{T}, i::Int=1, roots::Void=nothing) where {T} = RefArray{T,typeof(x),Void}(x, i, nothing)
 convert(::Type{Ref{T}}, x::AbstractArray{T}) where {T} = RefArray(x, 1)
-Ref(x::AbstractArray, i::Integer=1) = RefArray(x, i)
+Ref(x::AbstractArray, i::Integer) = RefArray(x, i)
 
 function unsafe_convert(P::Type{Ptr{T}}, b::RefArray{T}) where T
     if isbits(T)