Add generic == error

[lgoettgens]

Closes https://github.com/Nemocas/AbstractAlgebra.jl/pull/1800, resolves https://github.com/oscar-system/Oscar.jl/issues/4107.

This includes only the snippet from https://github.com/Nemocas/AbstractAlgebra.jl/pull/1800#issuecomment-2401919352

cc @joschmitt

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.52%. Comparing base (502745e) to head (aad74a9). Report is 129 commits behind head on master.

Files with missing lines	Patch %	Lines
src/fundamental_interface.jl	0.00%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1853      +/-   ##
==========================================
+ Coverage   88.14%   89.52%   +1.37%     
==========================================
  Files         119      126       +7     
  Lines       30019    37540    +7521     
==========================================
+ Hits        26460    33607    +7147     
- Misses       3559     3933     +374     

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[fingolfin]

This causes several errors in OscarCI, which actually make me wonder if there is a bug in code there. Perhaps @ThomasBreuer can have a look? For reference this is the error I see in CI:

Automorphism group of a perm. group or a (sub) pc group: Error During Test at /home/runner/work/AbstractAlgebra.jl/AbstractAlgebra.jl/oscar-dev/Oscar/test/Groups/homomorphisms.jl:700
  Test threw exception
  Expression: !(g in A)
  == is not implemented for the given types
  Stacktrace:
   [1] error(s::String)
     @ Base ./error.jl:35
   [2] ==(::AutomorphismGroupElem{PermGroup}, ::GAPGroupHomomorphism{PermGroup, PcGroup})
     @ AbstractAlgebra ~/work/AbstractAlgebra.jl/AbstractAlgebra.jl/src/fundamental_interface.jl:8
   [3] in(x::GAPGroupHomomorphism{PermGroup, PcGroup}, itr::AutomorphismGroup{PermGroup})
     @ Base ./operators.jl:1293
   [4] eval_test(evaluated::Expr, quoted::Expr, source::LineNumberNode, negate::Bool)
     @ Test /opt/hostedtoolcache/julia/1.10.5/x64/share/julia/stdlib/v1.10/Test/src/Test.jl:355
   [5] macro expansion
     @ /opt/hostedtoolcache/julia/1.10.5/x64/share/julia/stdlib/v1.10/Test/src/Test.jl:669 [inlined]
   [6] macro expansion
     @ ~/work/AbstractAlgebra.jl/AbstractAlgebra.jl/oscar-dev/Oscar/test/Groups/homomorphisms.jl:700 [inlined]
   [7] macro expansion
     @ /opt/hostedtoolcache/julia/1.10.5/x64/share/julia/stdlib/v1.10/Test/src/Test.jl:1577 [inlined]
   [8] top-level scope
     @ ~/work/AbstractAlgebra.jl/AbstractAlgebra.jl/oscar-dev/Oscar/test/Groups/homomorphisms.jl:660
Automorphism group of a perm. group or a (sub) pc group: Error During Test at /home/runner/work/AbstractAlgebra.jl/AbstractAlgebra.jl/oscar-dev/Oscar/test/Groups/homomorphisms.jl:700
  Test threw exception
  Expression: !(g in A)
  == is not implemented for the given types
  Stacktrace:
   [1] error(s::String)
     @ Base ./error.jl:35
   [2] ==(::AutomorphismGroupElem{PcGroup}, ::GAPGroupHomomorphism{PcGroup, PcGroup})
    @ Base ./asyncmap.jl:171
  [2] foreach(f::Base.var"#1033#1035", itr::Vector{Any})
    @ Base ./abstractarray.jl:3097
  [3] maptwice(wrapped_f::Function, chnl::Channel{Any}, worker_tasks::Vector{Any}, c::Vector{String})
    @ Base ./asyncmap.jl:171
  [4] wrap_n_exec_twice
    @ ./asyncmap.jl:147 [inlined]
  [5] #async_usemap#1018
    @ ./asyncmap.jl:97 [inlined]
  [6] async_usemap
    @ ./asyncmap.jl:78 [inlined]
  [7] #asyncmap#1017
    @ ./asyncmap.jl:75 [inlined]
  [8] asyncmap
    @ ./asyncmap.jl:74 [inlined]
  [9] pmap(f::Function, p::WorkerPool, c::Vector{String}; distributed::Bool, batch_size::Int64, on_error::Nothing, retry_delays::Vector{Any}, retry_check::Nothing)
    @ Distributed /opt/hostedtoolcache/julia/1.10.5/x64/share/julia/stdlib/v1.10/Distributed/src/pmap.jl:126
 [10] pmap(f::Function, p::WorkerPool, c::Vector{String})
    @ Distributed /opt/hostedtoolcache/julia/1.10.5/x64/share/julia/stdlib/v1.10/Distributed/src/pmap.jl:99
 [11] pmap(f::Function, c::Vector{String}; kwargs::@Kwargs{})
    @ Distributed /opt/hostedtoolcache/julia/1.10.5/x64/share/julia/stdlib/v1.10/Distributed/src/pmap.jl:156
 [12] top-level scope
    @ ~/work/AbstractAlgebra.jl/AbstractAlgebra.jl/oscar-dev/Oscar/test/runtests.jl:154
 [13] include(fname::String)
    @ Base.MainInclude ./client.jl:489
 [14] top-level scope
    @ none:6
in expression starting at /home/runner/work/AbstractAlgebra.jl/AbstractAlgebra.jl/oscar-dev/Oscar/test/runtests.jl:154
ERROR: Package Oscar errored during testing

[ThomasBreuer]

Perhaps @ThomasBreuer can have a look?

O.k.

I can reproduce the problem locally, and will create a pull request for Oscar.jl that fixes it.

[thofma]

Note that this does not address all of the problems, since it is still possible to compare elements with the same type but different parents.