Compact printing for Adjoint vectors, and Diagonal (#40722)

This changes the compact printing to preserve more information -- an
adjoint vector is not quite a matrix, and Diagonal wastes a lot of
space:
```julia
julia> (Diagonal(1:4), [5,6,7]', transpose(8:10))  # before
([1 0 0 0; 0 2 0 0; 0 0 3 0; 0 0 0 4], [5 6 7], [8 9 10])

julia> (Diagonal(1:4), [5,6,7]', transpose(8:10))  # after
(Diagonal(1:4), adjoint([5, 6, 7]), transpose(8:10))
```
Would have been better to do at the same time as 1.6's other printing
changes, I guess.

---------

Co-authored-by: Jishnu Bhattacharya <jishnub.github@gmail.com>

base/abstractarray.jl

@@ -1921,7 +1921,7 @@ julia> vcat(range(1, 2, length=3))  # collects lazy ranges
  2.0
 
 julia> two = ([10, 20, 30]', Float64[4 5 6; 7 8 9])  # row vector and a matrix
-([10 20 30], [4.0 5.0 6.0; 7.0 8.0 9.0])
+(adjoint([10, 20, 30]), [4.0 5.0 6.0; 7.0 8.0 9.0])
 
 julia> vcat(two...)
 3×3 Matrix{Float64}:

stdlib/LinearAlgebra/src/adjtrans.jl

@@ -302,6 +302,16 @@ function Base.showarg(io::IO, v::Transpose, toplevel)
     toplevel && print(io, " with eltype ", eltype(v))
     return nothing
 end
+function Base.show(io::IO, v::Adjoint{<:Real, <:AbstractVector})
+    print(io, "adjoint(")
+    show(io, parent(v))
+    print(io, ")")
+end
+function Base.show(io::IO, v::Transpose{<:Number, <:AbstractVector})
+    print(io, "transpose(")
+    show(io, parent(v))
+    print(io, ")")
+end
 
 # some aliases for internal convenience use
 const AdjOrTrans{T,S} = Union{Adjoint{T,S},Transpose{T,S}} where {T,S}

stdlib/LinearAlgebra/src/diagonal.jl

@@ -213,6 +213,11 @@ end
 function Base.replace_in_print_matrix(A::Diagonal,i::Integer,j::Integer,s::AbstractString)
     i==j ? s : Base.replace_with_centered_mark(s)
 end
+function Base.show(io::IO, A::Diagonal)
+    print(io, "Diagonal(")
+    show(io, A.diag)
+    print(io, ")")
+end
 
 parent(D::Diagonal) = D.diag
 

stdlib/LinearAlgebra/test/adjtrans.jl

@@ -532,6 +532,11 @@ end
     @test String(take!(io)) == "transpose(::Matrix{Float64})"
 end
 
+@testset "show" begin
+    @test repr(adjoint([1,2,3])) == "adjoint([1, 2, 3])"
+    @test repr(transpose([1f0,2f0])) == "transpose(Float32[1.0, 2.0])"
+end
+
 @testset "strided transposes" begin
     for t in (Adjoint, Transpose)
         @test strides(t(rand(3))) == (3, 1)

stdlib/LinearAlgebra/test/diagonal.jl

@@ -1231,6 +1231,11 @@ Base.size(::SMatrix1) = (1, 1)
     @test C isa Matrix{SMatrix1{String}}
 end
 
+@testset "show" begin
+    @test repr(Diagonal([1,2])) == "Diagonal([1, 2])"  # 2-arg show
+    @test contains(repr(MIME"text/plain"(), Diagonal([1,2])), "⋅  2")  # 3-arg show
+end
+
 @testset "copyto! with UniformScaling" begin
     @testset "Fill" begin
         for len in (4, InfiniteArrays.Infinity())