Make uniformscaling inequal to matrices (#37525)

Closes #35485

Author: jakobnissen

NEWS.md

@@ -39,6 +39,8 @@ Language changes
   a function like other operators. The dotted version `.-->` is now parsed as well.
   For backwards compatibility, `-->` still parses using its own expression head
   instead of `:call`.
+* Instances of `UniformScaling` are no longer `isequal` to matrices. Previous
+  behaviour violated the rule that `isequal(x, y)` implies `hash(x) == hash(y)`.
 
 Compiler/Runtime improvements
 -----------------------------

stdlib/LinearAlgebra/src/LinearAlgebra.jl

@@ -11,7 +11,7 @@ import Base: \, /, *, ^, +, -, ==
 import Base: USE_BLAS64, abs, acos, acosh, acot, acoth, acsc, acsch, adjoint, asec, asech,
     asin, asinh, atan, atanh, axes, big, broadcast, ceil, conj, convert, copy, copyto!, cos,
     cosh, cot, coth, csc, csch, eltype, exp, fill!, floor, getindex, hcat,
-    getproperty, imag, inv, isapprox, isone, iszero, IndexStyle, kron, kron!, length, log, map, ndims,
+    getproperty, imag, inv, isapprox, isequal, isone, iszero, IndexStyle, kron, kron!, length, log, map, ndims,
     oneunit, parent, power_by_squaring, print_matrix, promote_rule, real, round, sec, sech,
     setindex!, show, similar, sin, sincos, sinh, size, sqrt,
     strides, stride, tan, tanh, transpose, trunc, typed_hcat, vec

stdlib/LinearAlgebra/src/uniformscaling.jl

@@ -324,6 +324,9 @@ function ==(A::StridedMatrix, J::UniformScaling)
     return true
 end
 
+isequal(A::AbstractMatrix, J::UniformScaling) = false
+isequal(J::UniformScaling, A::AbstractMatrix) = false
+
 function isapprox(J1::UniformScaling{T}, J2::UniformScaling{S};
             atol::Real=0, rtol::Real=Base.rtoldefault(T,S,atol), nans::Bool=false) where {T<:Number,S<:Number}
     isapprox(J1.λ, J2.λ, rtol=rtol, atol=atol, nans=nans)

stdlib/LinearAlgebra/test/uniformscaling.jl

@@ -400,6 +400,13 @@ end
     @test 0denseI != 2I != 0denseI # test generic path / inequality on diag
     @test alltwos != 2I != alltwos # test generic path / inequality off diag
     @test rdenseI !=  I != rdenseI # test square matrix check
+
+    # isequal
+    @test !isequal(I, I(3))
+    @test !isequal(I(1), I)
+    @test !isequal([1], I)
+    @test isequal(I, 1I)
+    @test !isequal(2I, 3I)
 end
 
 @testset "operations involving I should preserve eltype" begin