Add news, test, doc

NEWS.md

@@ -31,6 +31,8 @@ New library functions
 Standard library changes
 ------------------------
 
+* A no-argument construct to `Ptr{T}` has been added which constructs a null pointer ([#30919])
+
 #### LinearAlgebra
 
 * Added keyword arguments `rtol`, `atol` to `pinv` and `nullspace` ([#29998]).
@@ -65,8 +67,19 @@ Deprecated or removed
 
 
 <!--- generated by NEWS-update.jl: -->
+[#24980]: https://github.com/JuliaLang/julia/issues/24980
 [#29998]: https://github.com/JuliaLang/julia/issues/29998
 [#30061]: https://github.com/JuliaLang/julia/issues/30061
 [#30200]: https://github.com/JuliaLang/julia/issues/30200
+[#30298]: https://github.com/JuliaLang/julia/issues/30298
 [#30323]: https://github.com/JuliaLang/julia/issues/30323
 [#30349]: https://github.com/JuliaLang/julia/issues/30349
+[#30372]: https://github.com/JuliaLang/julia/issues/30372
+[#30583]: https://github.com/JuliaLang/julia/issues/30583
+[#30584]: https://github.com/JuliaLang/julia/issues/30584
+[#30593]: https://github.com/JuliaLang/julia/issues/30593
+[#30618]: https://github.com/JuliaLang/julia/issues/30618
+[#30670]: https://github.com/JuliaLang/julia/issues/30670
+[#30712]: https://github.com/JuliaLang/julia/issues/30712
+[#30724]: https://github.com/JuliaLang/julia/issues/30724
+[#30919]: https://github.com/JuliaLang/julia/issues/30919

base/boot.jl

@@ -747,7 +747,6 @@ Int64(x::Ptr) = Int64(UInt32(x))
 UInt64(x::Ptr) = UInt64(UInt32(x))
 end
 Ptr{T}(x::Union{Int,UInt,Ptr}) where {T} = bitcast(Ptr{T}, x)
-Ptr{T}() where {T} = Ptr{T}(C_NULL)
 
 Signed(x::UInt8)    = Int8(x)
 Unsigned(x::Int8)   = UInt8(x)

base/pointer.jl

@@ -8,6 +8,13 @@ memory is actually valid, or that it actually represents data of the specified t
 """
 Ptr
 
+"""
+    Ptr{T}()
+
+Creates a null pointer to type `T`.
+"""
+Ptr{T}() where {T} = Ptr{T}(C_NULL)
+
 ## converting pointers to an appropriate unsigned ##
 
 """

test/misc.jl

@@ -730,3 +730,6 @@ end
     @test isless(b, a)
     @test sort([a, b]) == [b, a]
 end
+
+# Pointer 0-arg constructor
+@test Ptr{Cvoid}() == C_NULL