make checksquare fail on non-matrices (#1476)

Closes #1362

Author: araujoms

src/LinearAlgebra.jl

@@ -326,7 +326,7 @@ StridedMatrixStride1{T} = StridedArrayStride1{T,2}
 """
     LinearAlgebra.checksquare(A)
 
-Check that a matrix is square, then return its common dimension.
+Checks whether a matrix is square, returning its common dimension if it is the case, or throwing a DimensionMismatch error otherwise.
 For multiple arguments, return a vector.
 
 # Examples
@@ -340,19 +340,13 @@ julia> LinearAlgebra.checksquare(A, B)
 ```
 """
 function checksquare(A)
-    m,n = size(A)
-    m == n || throw(DimensionMismatch(lazy"matrix is not square: dimensions are $(size(A))"))
-    m
+    sizeA = size(A)
+    length(sizeA) == 2 || throw(DimensionMismatch(lazy"input is not a matrix: dimensions are $sizeA"))
+    sizeA[1] == sizeA[2] || throw(DimensionMismatch(lazy"matrix is not square: dimensions are $sizeA"))
+    return sizeA[1]
 end
 
-function checksquare(A...)
-    sizes = Int[]
-    for a in A
-        size(a,1)==size(a,2) || throw(DimensionMismatch(lazy"matrix is not square: dimensions are $(size(a))"))
-        push!(sizes, size(a,1))
-    end
-    return sizes
-end
+checksquare(A...) = [checksquare(a) for a in A]
 
 function char_uplo(uplo::Symbol)
     if uplo === :U

test/dense.jl

@@ -1430,4 +1430,15 @@ end
     @test log(D) ≈ log(UpperTriangular(D))
 end
 
+@testset "issue 1362" begin
+    A = zeros(2,2)
+    B = zeros(2,3)
+    C = zeros(2,2,1)
+    @test LinearAlgebra.checksquare(A) == 2
+    @test LinearAlgebra.checksquare(A,A) == [2, 2]
+    @test_throws DimensionMismatch LinearAlgebra.checksquare(B)
+    @test_throws DimensionMismatch LinearAlgebra.checksquare(C)
+    @test_throws DimensionMismatch LinearAlgebra.checksquare(A,B)
+end
+
 end # module TestDense