Replace LinearAlgebra._iszero by Base.iszero (#36194)

Author: blegat

stdlib/LinearAlgebra/src/structuredbroadcast.jl

@@ -104,9 +104,7 @@ function isstructurepreserving(::typeof(Base.literal_pow), ::Ref{typeof(^)}, ::S
 end
 isstructurepreserving(f, args...) = false
 
-_iszero(n::Number) = iszero(n)
-_iszero(x) = x == 0
-fzeropreserving(bc) = (v = fzero(bc); !ismissing(v) && _iszero(v))
+fzeropreserving(bc) = (v = fzero(bc); !ismissing(v) && iszero(v))
 # Like sparse matrices, we assume that the zero-preservation property of a broadcasted
 # expression is stable.  We can test the zero-preservability by applying the function
 # in cases where all other arguments are known scalars against a zero from the structured

stdlib/LinearAlgebra/test/structuredbroadcast.jl

@@ -205,4 +205,22 @@ end
     @test typeof(tmp) <: Tridiagonal
 
 end
+
+struct Zero end
+Base.iszero(::Zero) = true
+Base.zero(::Type{Zero}) = Zero()
+@testset "PR #36193" begin
+    z = Zero()
+    Z = [z z
+         z z]
+    zz = [z, z]
+    U = UpperTriangular(Z)
+    L = LowerTriangular(Z)
+    D = Diagonal(zz)
+    for a in [U, L, D]
+        @test identity.(a) isa typeof(a)
+        @test map(identity, a) isa typeof(a)
+    end
+end
+
 end