Fix #18742: Added check for / DimensionMismatch error (#30446)

* Added check for / DimensionMismatch error
* Added tests

Author: raghav9-97

stdlib/LinearAlgebra/src/generic.jl

@@ -908,7 +908,10 @@ function (\)(A::AbstractMatrix, B::AbstractVecOrMat)
 end
 
 (\)(a::AbstractVector, b::AbstractArray) = pinv(a) * b
-(/)(A::AbstractVecOrMat, B::AbstractVecOrMat) = copy(adjoint(adjoint(B) \ adjoint(A)))
+function (/)(A::AbstractVecOrMat, B::AbstractVecOrMat)
+    size(A,2) != size(B,2) && throw(DimensionMismatch("Both inputs should have the same number of columns"))
+    return copy(adjoint(adjoint(B) \ adjoint(A)))
+end
 # \(A::StridedMatrix,x::Number) = inv(A)*x Should be added at some point when the old elementwise version has been deprecated long enough
 # /(x::Number,A::StridedMatrix) = x*inv(A)
 /(x::Number, v::AbstractVector) = x*pinv(v)

stdlib/LinearAlgebra/src/qr.jl

@@ -854,7 +854,7 @@ function (\)(A::Union{QR{TA},QRCompactWY{TA},QRPivoted{TA}}, B::AbstractVecOrMat
     @assert !has_offset_axes(B)
     S = promote_type(TA,TB)
     m, n = size(A)
-    m == size(B,1) || throw(DimensionMismatch("left hand side has $m rows, but right hand side has $(size(B,1)) rows"))
+    m == size(B,1) || throw(DimensionMismatch("Both inputs should have the same number of rows"))
 
     AA = Factorization{S}(A)
 

stdlib/LinearAlgebra/test/generic.jl

@@ -299,6 +299,10 @@ LinearAlgebra.Transpose(a::ModInt{n}) where {n} = transpose(a)
     @test A*(lu(A, Val(true))\b) == b
 end
 
+@testset "Issue 18742" begin
+    @test_throws DimensionMismatch ones(4,5)/zeros(3,6)
+    @test_throws DimensionMismatch ones(4,5)\zeros(3,6)
+end
 @testset "fallback throws properly for AbstractArrays with dimension > 2" begin
     @test_throws ErrorException adjoint(rand(2,2,2,2))
     @test_throws ErrorException transpose(rand(2,2,2,2))