Drop support for Base.tail()

[JamesWrigley]

This causes invalidations and should not be needed anymore by ChainRules.jl since the rule that uses it: #576 (comment)
Was deleted in JuliaDiff/ChainRules.jl#680.

I ran this on the ChainRules.jl tests and saw a ton of failures locally (also seen in CI), but none that seem related to this change. Disclaimer: I have almost no understanding of this kind of thing 🙈

Fixes #576.

Fixes these invalidations seen in CurveFit.jl:

 inserting tail(t::ChainRulesCore.Tangent{<:NamedTuple{<:Any, <:Tuple{}}}) @ ChainRulesCore ~/.julia/packages/ChainRulesCore/Vsbj9/src/tangent_types/structural_tangent.jl:378 invalidated:                                                                                                                                    
   mt_backedges:  1: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{Tuple{Int64}, Vararg{Any}}, ::Any) (0 children)                                                                                                                                                   
                  2: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Int64}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Missing) (0 children)                                                                                                   
                  3: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Int64}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Bool) (0 children)                                                                                                      
                  4: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_interleave(::NamedTuple, ::Any, ::Tuple{Bool, Vararg{Any}}) (0 children)                                                                                                                                 
                  5: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_interleave(::Any, ::Any, ::Any) (0 children)                                                                                                                                                             
                  6: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{NTuple{4, Symbol}, Vararg{Any}}, ::Any) (0 children)                                                                                                                                              
                  7: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{NTuple{4, Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Missing) (0 children)                                                                                              
                  8: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Any, ::Any, ::Tuple{Any, Vararg{Any}}, ::Bool) (0 children)                                                                                                                                       
                  9: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{NTuple{4, Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Bool) (0 children)                                                                                                 
                 10: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{Tuple{Symbol}, Vararg{Any}}, ::Any) (0 children)                                                                                                                                                  
                 11: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Missing) (0 children)                                                                                                  
                 12: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Any, ::Any, ::Tuple{Any, Vararg{Any}}, ::Bool) (0 children)                                                                                                                                       
                 13: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Bool) (0 children)                                                                                                     
                 14: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{Tuple{Symbol, Symbol, Symbol}, Vararg{Any}}, ::Any) (0 children)                                                                                                                                  
                 15: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Symbol, Symbol, Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Missing) (0 children)                                                                                  
                 16: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Any, ::Any, ::Tuple{Any, Vararg{Any}}, ::Bool) (0 children)                                                                                                                                       
                 17: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Symbol, Symbol, Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Bool) (0 children)                                                                                     
                 18: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{Tuple{Symbol, Symbol}, Vararg{Any}}, ::Any) (0 children)                                                                                                                                          
                 19: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Symbol, Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Missing) (0 children)                                                                                          
                 20: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Any, ::Any, ::Tuple{Any, Vararg{Any}}, ::Bool) (0 children)                                                                                                                                       
                 21: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Symbol, Symbol}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Bool) (0 children)                                                                                             
                 22: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{Tuple{Int64, Int64}, Vararg{Any}}, ::Any) (0 children)                                                                                                                                            
                 23: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Int64, Int64}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Missing) (0 children)                                                                                            
                 24: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Any, ::Any, ::Tuple{Any, Vararg{Any}}, ::Bool) (0 children)                                                                                                                                       
                 25: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple{Tuple{Int64, Int64}, Vararg{Any}}, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Bool) (0 children)                                                                                               
                 26: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{Tuple{}, Vararg{Tuple{}}}, ::Any) (0 children)                                                                                                                                                    
                 27: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::Base.LogicalIndex, ::Any) (0 children)                                                                                                                                                                                     
                 28: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Float64}, ::Any) (0 children)                                                                                                                                                                                
                 29: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{String}, ::Any) (1 children)                                                                                                                                                                                 
                 30: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_interleave(::NamedTuple, ::Any, ::Any) (1 children)                                                                                                                                                      
                 31: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_interleave(::Any, ::Any, ::NamedTuple) (1 children)                                                                                                                                                      
                 32: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::Base.Iterators.Enumerate{Vector{Any}}, ::Any) (2 children)                                                                                                                                                                 
                 33: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Compiler.MethodMatchInfo}, ::Any) (4 children)                                                                                                                                                               
                 34: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Compiler.ApplyCallInfo}, ::Any) (4 children)                                                                                                                                                                 
                 35: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Union{Nothing, Compiler.ConstResult}}, ::Any) (4 children)                                                                                                                                                   
                 36: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Union{Nothing, Compiler.AbstractIterationInfo}}, ::Any) (4 children)                                                                                                                                         
                 37: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Compiler.CallMeta}, ::Any) (4 children)                                                                                                                                                                      
                 38: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Compiler.NewPhiCNode2}, ::Any) (4 children)                                                                                                                                                                  
                 39: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Tuple{LineNumberNode, Expr}}, ::Any) (4 children)                                                                                                                                                            
                 40: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple{Vararg{Tuple{}}}, ::Any) (4 children)                                                                                                                                                             
                 41: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::Base.Iterators.Enumerate, ::Any) (5 children)                                                                                              
                 42: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_interleave(::NamedTuple, ::NamedTuple, ::Any) (5 children)                                                               
                 43: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::NamedTuple, ::Any, ::Tuple{Bool, Vararg{Any}}, ::Bool) (5 children)                                               
                 44: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::NamedTuple, ::Any, ::Tuple{Any, Vararg{Any}}, ::Bool) (5 children)                                                
                 45: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Broadcast.check_broadcast_shape(::Any, ::Tuple{Base.OneTo{Int64}}) (5 children)                                                                 
                 46: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for axes(::Base.ReinterpretArray{Float64, 1, S, A, true} where A<:Union{SubArray{S, N, A, I, true} where {N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray{S}}) where S (5 children)
                 47: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::SubArray{T, 1} where T, ::Tuple{Any, Vararg{Any}}) (6 children)                                                                            
                 48: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Any, ::NamedTuple, ::Tuple{Bool, Vararg{Any}}, ::Bool) (10 children)                                              
                 49: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for size(::Base.ReinterpretArray{Float64, N, S, A, true} where {N, A<:Union{SubArray{S, N, A, I, true} where {N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray{S}}}) where S (10 child
ren)                                                                                                                                                                                                                                                                              
                 50: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Tuple, ::Any, ::Tuple{Missing, Vararg{Any}}, ::Missing) (12 children)                                             
                 51: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::SubArray{T, 1} where T, ::Tuple{Any}) (15 children)                                                                                        
                 52: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base._overflowind(::Any, ::Any, ::NTuple{N, Int64} where N) (15 children)                                                                            
                 53: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for iterate(::AbstractRange{Any}, ::Any) (25 children)                                                                                                   
                 54: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_isdone(::Tuple, ::Any) (38 children)                                                                                             
                 55: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base.Iterators._zip_iterate_some(::Any, ::NamedTuple, ::Tuple{Any, Vararg{Any}}, ::Bool) (50 children)                                               
                 56: signature Tuple{typeof(Base.tail), Any} triggered MethodInstance for Base._cshp(::Int64, ::Tuple{Bool}, ::Tuple{Int64}, ::Any) (66 children)   

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.52%. Comparing base (004e43e) to head (10e0ec5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #703      +/-   ##
==========================================
+ Coverage   93.49%   93.52%   +0.03%     
==========================================
  Files          15       15              
  Lines         999      989      -10     
==========================================
- Hits          934      925       -9     
+ Misses         65       64       -1     

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[JamesWrigley]

The number of failures is a bit disturbing, but they don't seem related to this PR (and they also show up on other PRs).

[devmotion]

Sorry, I mis-clicked. IMO it would be great if we could remove these definitions. There are unfortunately preexisting test failures IIRC. I'll have a closer look tomorrow.

[devmotion]

This looks fine to me. The test errors seem unrelated, in many cases caused by Aqua tests and in particular without any reference to tail.

It would be good to fix the doctest failures though, such that we're able to build docs for the upcoming release. Can you update the doctests (see https://documenter.juliadocs.org/stable/man/doctests/#Fixing-Outdated-Doctests)?

[JamesWrigley]

Ah yeah sure, fixed them in eb83113. BTW one of them was using rand(), I replaced that with a constant to avoid the tests breaking again if the RNG changes.

[devmotion]

I'd suggest

Suggested change

	julia> t = @thunk(3)
	Thunk(var"#4#5"())
	Thunk(var"#2#3"())
	julia> t = @thunk(3);

or a doctest filter. But I think removing the output is simpler.

[JamesWrigley]

Yeah good idea, fixed in c2e51fd.

[devmotion]

Can you update the version number?

[JamesWrigley]

Sure, done in 10e0ec5.

[devmotion]

This is a breaking change - it will definitely break older ChainRules releases and it might break packages that define rules using Base.tail.

Suggested change

	version = "1.26.1"
	version = "2.0.0"

[JamesWrigley]

Ah ok, fixed in 09cb407.

[JamesWrigley]

I also removed the compat bound in docs/Project.toml so that the docs will build. There's quite a few more failing tests now, I guess because downstream packages aren't compatible anymore.