upgrade to at-layer macro, replaces at-functor

fixup

tidy up, add NEWS

review suggestions

macro docstring, incl. hcat(3.3)

Author: mcabbott

NEWS.md

@@ -2,6 +2,10 @@
 
 See also [github's page](https://github.com/FluxML/Flux.jl/releases) for a complete list of PRs merged before each release.
 
+## v0.14.13
+* New macro `Flux.@layer` which should be used in place of `@functor`.
+  This also adds `show` methods for pretty printing.
+
 ## v0.14.0 (July 2023)
 * Flux now requires julia v1.9 or later.
 * CUDA.jl is not a hard dependency anymore. Support is now provided through the extension mechanism, by loading `using Flux, CUDA`.
@@ -51,6 +55,7 @@ See also [github's page](https://github.com/FluxML/Flux.jl/releases) for a compl
 
 ## v0.13.6
 * Use the package [OneHotArrays.jl](https://github.com/FluxML/OneHotArrays.jl) instead of having the same code here.
+* Added [`@autosize` macro](https://github.com/FluxML/Flux.jl/pull/2078)
 
 ## v0.13.4
 * Added [`PairwiseFusion` layer](https://github.com/FluxML/Flux.jl/pull/1983)

docs/src/models/advanced.md

@@ -18,8 +18,8 @@ function (m::CustomModel)(x)
   return m.chain(x) + x
 end
 
-# Call @functor to allow for training. Described below in more detail.
-Flux.@functor CustomModel
+# Call @layer to allow for training. Described below in more detail.
+Flux.@layer CustomModel
 ```
 
 You can then use the model like:
@@ -39,15 +39,15 @@ Taking reference from our example `Affine` layer from the [basics](@ref man-basi
 By default all the fields in the `Affine` type are collected as its parameters, however, in some cases it may be desired to hold other metadata in our "layers" that may not be needed for training, and are hence supposed to be ignored while the parameters are collected. With Flux, the way to mark some fields of our layer as trainable is through overloading the `trainable` function:
 
 ```julia-repl
-julia> Flux.@functor Affine
+julia> @layer Affine
 
 julia> a = Affine(Float32[1 2; 3 4; 5 6], Float32[7, 8, 9])
 Affine(Float32[1.0 2.0; 3.0 4.0; 5.0 6.0], Float32[7.0, 8.0, 9.0])
 
 julia> Flux.params(a) # default behavior
 Params([Float32[1.0 2.0; 3.0 4.0; 5.0 6.0], Float32[7.0, 8.0, 9.0]])
 
-julia> Flux.trainable(a::Affine) = (; a.W)  # returns a NamedTuple using the field's name
+julia> Flux.trainable(a::Affine) = (; W = a.W)  # returns a NamedTuple using the field's name
 
 julia> Flux.params(a)
 Params([Float32[1.0 2.0; 3.0 4.0; 5.0 6.0]])
@@ -67,7 +67,21 @@ julia> Flux.params(Affine(true, [10, 11, 12.0]))
 Params([])
 ```
 
-It is also possible to further restrict what fields are seen by writing `@functor Affine (W,)`. However, this is not recommended. This requires the `struct` to have a corresponding constructor that accepts only `W` as an argument, and the ignored fields will not be seen by functions like `gpu` (which is usually undesired).
+The exact same method of `trainable` can also be defined using the macro, for convenience:
+
+```julia
+Flux.@layer Affine trainable=(W,)
+```
+
+There is a second, more severe, kind of restriction possible:
+
+```
+Flux.@layer Affine children=(W,)
+```
+
+This is equivalent to `Functors.@functor Affine (W,)`. It means that all no exploration of the model will ever visit the other fields: They will not be moved to the GPU by [`gpu`](@ref), and their precision will not be changed by `f32`. This is not usually recommended.
+ This is generally not recommended. It requires the `struct` to have a corresponding constructor that accepts only `W` as an argument.
+
 
 ## Freezing Layer Parameters
 
@@ -135,9 +149,9 @@ Join(combine, paths...) = Join(combine, paths)
 ```
 Notice that we parameterized the type of the `paths` field. This is necessary for fast Julia code; in general, `T` might be a `Tuple` or `Vector`, but we don't need to pay attention to what it specifically is. The same goes for the `combine` field.
 
-The next step is to use [`Functors.@functor`](@ref) to make our struct behave like a Flux layer. This is important so that calling `params` on a `Join` returns the underlying weight arrays on each path.
+The next step is to use [`Functors.@layer`](@ref) to make our struct behave like a Flux layer. This is important so that calling `params` on a `Join` returns the underlying weight arrays on each path.
 ```julia
-Flux.@functor Join
+Flux.@layer Join
 ```
 
 Finally, we define the forward pass. For `Join`, this means applying each `path` in `paths` to each input array, then using `combine` to merge the results.
@@ -194,7 +208,7 @@ model(xs)
 
 Our custom `Split` layer will accept a single input, then pass the input through a separate path to produce multiple outputs.
 
-We start by following the same steps as the `Join` layer: define a struct, use [`Functors.@functor`](@ref), and define the forward pass.
+We start by following the same steps as the `Join` layer: define a struct, use [`@layer`](@ref), and define the forward pass.
 ```julia
 using Flux
 using CUDA
@@ -206,7 +220,7 @@ end
 
 Split(paths...) = Split(paths)
 
-Flux.@functor Split
+Flux.@layer Split
 
 (m::Split)(x::AbstractArray) = map(f -> f(x), m.paths)
 ```

docs/src/models/basics.md

@@ -257,8 +257,8 @@ m(5) # => 26
 
 There is still one problem with this `Affine` layer, that Flux does not know to look inside it. This means that [`Flux.train!`](@ref) won't see its parameters, nor will [`gpu`](@ref) be able to move them to your GPU. These features are enabled by the [`@functor`](@ref Functors.@functor) macro:
 
-```
-Flux.@functor Affine
+```julia
+Flux.@layer Affine
 ```
 
 Finally, most Flux layers make bias optional, and allow you to supply the function used for generating random weights. We can easily add these refinements to the `Affine` layer as follows, using the helper function [`create_bias`](@ref Flux.create_bias):
@@ -272,3 +272,8 @@ end
 
 Affine(3 => 1, bias=false, init=ones) |> gpu
 ```
+
+```@docs
+Flux.@layer
+Flux.create_bias
+```

src/Flux.jl

@@ -9,6 +9,7 @@ using MacroTools: @forward
 
 @reexport using NNlib
 using MLUtils
+const stack = MLUtils.stack  # now exported by Base
 import Optimisers: Optimisers, trainable, destructure  # before v0.13, Flux owned these functions
 using Optimisers: freeze!, thaw!, adjust!
 using Random: default_rng
@@ -69,14 +70,16 @@ include("functor.jl")
 # Pirate error to catch a common mistake.
 Functors.functor(::Type{<:MLUtils.DataLoader}, x) = error("`DataLoader` does not support Functors.jl, thus functions like `Flux.gpu` will not act on its contents.")
 
+include("layers/show.jl")
+include("layers/macro.jl")
+
 include("layers/stateless.jl")
 include("layers/basic.jl")
 include("layers/conv.jl")
 include("layers/recurrent.jl")
 include("layers/normalise.jl")
 include("layers/upsample.jl")
 include("layers/attention.jl")
-include("layers/show.jl")
 
 include("loading.jl")
 

src/functor.jl

@@ -81,6 +81,7 @@ function params!(p::Params, x, seen = IdSet())
   elseif x in seen
     nothing
   else
+    _check_new_macro(x)  # complains if you used @functor not @layer
     push!(seen, x)
     for child in trainable(x)
       params!(p, child, seen)

src/layers/basic.jl

@@ -46,7 +46,7 @@ end
 @forward Chain.layers Base.getindex, Base.length, Base.first, Base.last,
   Base.iterate, Base.lastindex, Base.keys, Base.firstindex
 
-@functor Chain
+@layer :expand Chain  # the + opts-in to container-style pretty-printing
 
 (c::Chain)(x) = _applychain(c.layers, x)
 
@@ -165,7 +165,7 @@ function Dense((in, out)::Pair{<:Integer, <:Integer}, σ = identity;
   Dense(init(out, in), bias, σ)
 end
 
-@functor Dense
+@layer Dense
 
 function (a::Dense)(x::AbstractVecOrMat)
   _size_check(a, x, 1 => size(a.weight, 2))
@@ -251,7 +251,7 @@ end
 Scale(s1::Integer, s23::Integer...; bias = true, init = ones32, _act = identity) = Scale(init(s1, s23...), bias, _act)
 Scale(size_act...; bias = true, init = ones32) = Scale(size_act[1:end-1]...; bias, init, _act = size_act[end])
 
-@functor Scale
+@layer Scale
 
 function (a::Scale)(x::AbstractArray)
   σ = NNlib.fast_act(a.σ, x)  # replaces tanh => tanh_fast, etc
@@ -306,7 +306,7 @@ end
 Maxout(layers...) = Maxout(layers)
 Maxout(f::Function, n_alts::Integer) = Maxout((f() for _ in 1:n_alts)...)
 
-@functor Maxout
+@layer :expand Maxout
 
 function (mo::Maxout)(input::AbstractArray)
   # Perhaps surprisingly, pairwise max broadcast is often faster,
@@ -353,7 +353,7 @@ struct SkipConnection{T,F}
   connection::F  #user can pass arbitrary connections here, such as (a,b) -> a + b
 end
 
-@functor SkipConnection
+@layer :expand SkipConnection
 
 function (skip::SkipConnection)(input)
   skip.connection(skip.layers(input), input)
@@ -423,7 +423,7 @@ struct Bilinear{F,A,B}
   end
 end
 
-@functor Bilinear
+@layer Bilinear
 
 function Bilinear(((in1, in2), out)::Pair{<:Tuple, <:Integer}, σ = identity;
                   bias = true, init = glorot_uniform)
@@ -522,7 +522,7 @@ function Parallel(connection; kw...)
   Parallel(connection, layers)
 end
 
-@functor Parallel
+@layer :expand Parallel
 
 (m::Parallel)(x) = m.connection(map(f -> f(x), Tuple(m.layers))...)
 (m::Parallel)(xs::Tuple) = m(xs...)
@@ -643,7 +643,7 @@ end
 end
 applypairwisefusion(layers::NamedTuple, connection, x) = applypairwisefusion(Tuple(layers), connection, x)
 
-@functor PairwiseFusion
+@layer :expand PairwiseFusion
 
 Base.getindex(m::PairwiseFusion, i) = m.layers[i]
 Base.getindex(m::PairwiseFusion, i::AbstractVector) = PairwiseFusion(m.connection, m.layers[i])
@@ -701,7 +701,7 @@ struct Embedding{W<:AbstractMatrix}
   weight::W
 end
 
-@functor Embedding
+@layer Embedding
 
 Embedding((in, out)::Pair{<:Integer, <:Integer}; init = randn32) = Embedding(init(out, in))
 

src/layers/conv.jl

@@ -187,7 +187,7 @@ function convfilter(filter::NTuple{N,Integer}, ch::Pair{<:Integer,<:Integer};
   init(filter..., cin÷groups, cout)
 end
 
-@functor Conv
+@layer Conv
 
 conv_dims(c::Conv, x::AbstractArray) =
   DenseConvDims(x, c.weight; stride = c.stride, padding = c.pad, dilation = c.dilation, groups = c.groups)
@@ -309,7 +309,7 @@ function ConvTranspose(k::NTuple{N,Integer}, ch::Pair{<:Integer,<:Integer}, σ =
   ConvTranspose(weight, bias, σ; stride, pad, dilation, groups)
 end
 
-@functor ConvTranspose
+@layer ConvTranspose
 
 function conv_transpose_dims(c::ConvTranspose, x::AbstractArray)
   # Calculate size of "input", from ∇conv_data()'s perspective...
@@ -460,7 +460,7 @@ function CrossCor(k::NTuple{N,Integer}, ch::Pair{<:Integer,<:Integer}, σ = iden
   return CrossCor(weight, bias, σ; stride, pad, dilation)
 end
 
-@functor CrossCor
+@layer CrossCor
 
 function crosscor(x, w, ddims::DenseConvDims)
   ddims = DenseConvDims(ddims, F=true)