slightly better abstract definition

but not reliably inferable for nested structures

base/abstractarray.jl

@@ -1141,7 +1141,14 @@ parts can specialize this method to return the concatenation of the `dataids` of
 their component parts.  A typical definition for an array that wraps a parent is
 `Base.dataids(C::CustomArray) = dataids(C.parent)`.
 """
-dataids(A::AbstractArray) = (UInt(pointer_from_objref(A)),)
+function dataids(A::AbstractArray)
+    @_inline_meta
+    ids = _splatmap(dataids, ntuple(i -> getfield(A, i), Val(nfields(A))))
+    if !isimmutable(A)
+        ids = (UInt(pointer_from_objref(A)), ids...)
+    end
+    return ids
+end
 dataids(A::Array) = (UInt(pointer(A)),)
 dataids(::AbstractRange) = ()
 dataids(x) = ()

test/abstractarray.jl

@@ -902,3 +902,56 @@ end
     @test hcat(1:2, fill(1, (2,1))) == hcat([1:2;], fill(1, (2,1))) == reshape([1,2,1,1],2,2)
     @test [(1:3) (4:6); fill(1, (3,2))] == reshape([1,2,3,1,1,1,4,5,6,1,1,1], 6,2)
 end
+
+# Ensure dataids are inferrable for custom arrays
+struct M0 <: AbstractArray{Int,2} end
+struct M1{T} <: AbstractArray{Int,2}
+    x::T
+end
+struct M2{T,S} <: AbstractArray{Int,2}
+    x::T
+    y::S
+end
+struct M10{A,B,C,D,E,F,G,H,I,J} <: AbstractArray{Int,2}
+    a::A
+    b::B
+    c::C
+    d::D
+    e::E
+    f::F
+    g::G
+    h::H
+    i::I
+    j::J
+end
+@testset "dataids" begin
+    @test @inferred(Base.dataids(M0())) === ()
+    @test @inferred(Base.dataids(M1(1))) === ()
+    @test @inferred(Base.dataids(M1(1:10))) === ()
+    @test @inferred(Base.dataids(M10(1,2,3,4,5,6,7,8,9,0))) === ()
+
+    @test @inferred(Base.dataids(M1(M1([1])))) != Base.dataids(M1(M1([1])))
+    @test @inferred(Base.dataids(M1(M2([1],2)))) != Base.dataids(M1(M2([1],2)))
+    @test @inferred(Base.dataids(M1(M2([1],[2])))) != Base.dataids(M1(M2([1],[2])))
+    @test @inferred(Base.dataids(M10([1],[2],[3],[4],[5],[6],[7],[8],[9],[0]))) != Base.dataids(M10([1],[2],[3],[4],[5],[6],[7],[8],[9],[0]))
+
+    x = [1]
+    y = [1]
+    mx = M1(x)
+    mxx = M2(x,x)
+    mxy = M2(x,y)
+    @test @inferred(Base.mightalias(mx,mx))
+    @test @inferred(Base.mightalias(mx,mxx))
+    @test @inferred(Base.mightalias(mx,mxy))
+    @test @inferred(Base.mightalias(mxx,x))
+    @test @inferred(Base.mightalias(x,mxy))
+    @test !@inferred(Base.mightalias(mx, y))
+    @test !@inferred(Base.mightalias(mxx, y))
+    @test !@inferred(Base.mightalias(mxx, [1]))
+    @test !@inferred(Base.mightalias(mxy, 1:10))
+    @test !@inferred(Base.mightalias(mxy, M0()))
+    @test !@inferred(Base.mightalias(mxy, [1]))
+    @test !@inferred(Base.mightalias(mxy, M1(1:10)))
+    @test !@inferred(Base.mightalias(mxy, M1([1])))
+end
+