custom getproperty of mutable struct fails

[marius311]

Here's a MWE on 0.4.20, basically I'm adding a custom property foo.x:

mutable struct Foo end
Base.getproperty(foo::Foo, k::Symbol) = k == :x ? 5 : getfield(foo,k)
Base.propertynames(::Foo) = (:x,)

foo = Foo()
gradient(y -> foo.x * y, 1)

which fails with:

ERROR: type Tuple has no field x
Stacktrace:
 [1] (::Zygote.var"#back#1962"{:x,Zygote.Context,Foo,Int64})(::Int64) at /home/marius/.julia/packages/Zygote/YeCEW/src/lib/lib.jl:212
 [2] #130#back at /home/marius/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49 [inlined]
 [3] #15 at ./none:1 [inlined]
 [4] (::typeof(∂(#15)))(::Int64) at /home/marius/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [5] (::Zygote.var"#36#37"{typeof(∂(#15))})(::Int64) at /home/marius/.julia/packages/Zygote/YeCEW/src/compiler/interface.jl:46
 [6] gradient(::Function, ::Int64) at /home/marius/.julia/packages/Zygote/YeCEW/src/compiler/interface.jl:55
 [7] top-level scope at none:0

Note if I make the struct immutable its fine. Another solution appears to be defining the following, but I really don't know what I'm doing here so maybe this is not correct in general:

Zygote.grad_mut(foo::Foo) = Ref{Any}((;(propertynames(foo) .=> nothing)...))

[ablaom]

Also running into this issue. Prevents use of Zygote with matrices wrapped as tables using Tables.matrix, for example.

In my case the struct is immutable and the error is still there (Zygote = v0.5.6):

struct Foo
    z::Float64
end

Base.propertynames(Foo) = (:z_squared,)
Base.getproperty(f::Foo, s::Symbol) =
    s in propertynames(Foo) ? getfield(f, :z)^2 : throw(ArgumentError)

foo = Foo(2.0)
julia> foo.z_squared
4.0

loss(x) = x*getfield(foo, :z)
julia> loss(3)
6.0

julia> gradient(loss, 1.0)
ERROR: ArgumentError
Stacktrace:
 [1] getproperty(::Foo, ::Symbol) at ./REPL[11]:1
 [2] adjoint at /Users/anthony/.julia/packages/Zygote/Xgcgs/src/lib/lib.jl:197 [inlined]
 [3] _pullback(::Zygote.Context, ::typeof(ZygoteRules.literal_getproperty), ::Foo, ::Val{:z at /Users/anthony/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:47
 [4] _pullback(::Zygote.Context, ::typeof(getfield), ::Foo, ::Symbol) at /Users/anthony/.julia/packages/Zygote/Xgcgs/src/lib/lib.jl:214
 [5] loss at ./REPL[20]:1 [inlined]
 [6] _pullback(::Zygote.Context, ::typeof(loss), ::Float64) at /Users/anthony/.julia/packages/Zygote/Xgcgs/src/compiler/interface2.jl:0
 [7] _pullback(::Function, ::Float64) at /Users/anthony/.julia/packages/Zygote/Xgcgs/src/compiler/interface.jl:38
 [8] pullback(::Function, ::Float64) at /Users/anthony/.julia/packages/Zygote/Xgcgs/src/compiler/interface.jl:44
 [9] gradient(::Function, ::Float64) at /Users/anthony/.julia/packages/Zygote/Xgcgs/src/compiler/interface.jl:53
 [10] top-level scope at REPL[23]:1
 [11] eval(::Module, ::Any) at ./boot.jl:331
 [12] eval_user_input(::Any, ::REPL.REPLBackend) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.4/REPL/src/REPL.jl:86
 [13] run_backend(::REPL.REPLBackend) at /Users/anthony/.julia/packages/Revise/BqeJF/src/Revise.jl:1184

julia> versioninfo()
Julia Version 1.4.2

[marius311]

Both MWEs from this issue appear fixed with at least Zygote v0.6.11 (maybe before, I havent bisected), so closing this issue.