Prune LinearAlgebra module in ambiguity test

[jishnub]

The ambiguity check was being run in a separate process, but it was not pruning the LinearAlgebra module. This was therefore not testing for ambiguities in the latest code, but the one in the sysimg.

The PR would be able to replicate the test failure seen in https://buildkite.com/julialang/julia-master/builds/47424#0196c03a-2230-4d64-b404-e04dbfc76c3f

[jishnub]

I don't understand the ambiguities here, but splitting the methods seems to resolve it.
The ambiguities on master (and on 79ba4de) were

julia> Test.detect_ambiguities(LinearAlgebra)
2-element Vector{Tuple{Method, Method}}:
 (/(u::Transpose{T, <:AbstractVector} where T, A::AbstractMatrix) @ LinearAlgebra ~/Dropbox/JuliaPackages/LinearAlgebra.jl/src/adjtrans.jl:543, /(B::AbstractMatrix, H::Union{Adjoint{<:Any, <:UpperHessenberg}, Transpose{<:Any, <:UpperHessenberg}, UpperHessenberg}) @ LinearAlgebra ~/Dropbox/JuliaPackages/LinearAlgebra.jl/src/hessenberg.jl:185)
 (/(u::Adjoint{T, <:AbstractVector} where T, A::AbstractMatrix) @ LinearAlgebra ~/Dropbox/JuliaPackages/LinearAlgebra.jl/src/adjtrans.jl:542, /(B::AbstractMatrix, H::Union{Adjoint{<:Any, <:UpperHessenberg}, Transpose{<:Any, <:UpperHessenberg}, UpperHessenberg}) @ LinearAlgebra ~/Dropbox/JuliaPackages/LinearAlgebra.jl/src/hessenberg.jl:185)

However, the following all work:

julia> U = UpperHessenberg(rand(4,4));

julia> (1:4)' / U;

julia> (1:4)' / U';

julia> (1:4)' / transpose(U);

julia> transpose(1:4) / U';

julia> transpose(1:4) / transpose(U);

julia> transpose(1:4) / U;

as there are specialized methods for these:

LinearAlgebra.jl/src/hessenberg.jl

Lines 195 to 201 in 3393398

	# fix method ambiguities for right division, from adjtrans.jl:
	/(u::AdjointAbsVec, A::UpperHessenberg) = adjoint(adjoint(A) \ u.parent)
	/(u::TransposeAbsVec, A::UpperHessenberg) = transpose(transpose(A) \ u.parent)
	/(u::AdjointAbsVec, A::Adjoint{<:Any,<:UpperHessenberg}) = adjoint(adjoint(A) \ u.parent)
	/(u::TransposeAbsVec, A::Transpose{<:Any,<:UpperHessenberg}) = transpose(transpose(A) \ u.parent)
	/(u::AdjointAbsVec, A::Transpose{<:Any,<:UpperHessenberg}) = adjoint(conj(A.parent) \ u.parent) # technically should be adjoint(copy(adjoint(copy(A))) \ u.parent)
	/(u::TransposeAbsVec, A::Adjoint{<:Any,<:UpperHessenberg}) = transpose(conj(A.parent) \ u.parent)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.74%. Comparing base (2cb1e98) to head (376d885).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1349   +/-   ##
=======================================
  Coverage   93.74%   93.74%           
=======================================
  Files          34       34           
  Lines       15753    15755    +2     
=======================================
+ Hits        14768    14770    +2     
  Misses        985      985           

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