Copy matrices in triu/tril if no zero exists

Author: jishnub

src/dense.jl

@@ -124,6 +124,17 @@ haszero(::Type) = false
 haszero(::Type{T}) where {T<:Number} = isconcretetype(T)
 haszero(::Type{Union{Missing,T}}) where {T<:Number} = haszero(T)
 @propagate_inbounds _zero(M::AbstractArray{T}, inds...) where {T} = haszero(T) ? zero(T) : zero(M[inds...])
+function zero!(M::AbstractArray{T}) where {T}
+    if haszero(T)
+        fill!(M, zero(T))
+    else
+        for i in eachindex(M)
+            v = @inbounds M[i]
+            z = zero(v)
+            @inbounds M[i] = z
+        end
+    end
+end
 
 """
     triu!(M, k::Integer)

src/diagonal.jl

@@ -279,7 +279,7 @@ function triu!(D::Diagonal{T}, k::Integer=0) where T
         throw(ArgumentError(string("the requested diagonal, $k, must be at least ",
             "$(-n + 1) and at most $(n + 1) in an $n-by-$n matrix")))
     elseif k > 0
-        fill!(D.diag, zero(T))
+        zero!(D.diag)
     end
     return D
 end
@@ -290,7 +290,7 @@ function tril!(D::Diagonal{T}, k::Integer=0) where T
         throw(ArgumentError(LazyString(lazy"the requested diagonal, $k, must be at least ",
             lazy"$(-n - 1) and at most $(n - 1) in an $n-by-$n matrix")))
     elseif k < 0
-        fill!(D.diag, zero(T))
+        zero!(D.diag)
     end
     return D
 end

src/generic.jl

@@ -466,6 +466,11 @@ julia> triu(a,-3)
 """
 function triu(M::AbstractMatrix, k::Integer = 0)
     d = similar(M)
+    if !haszero(eltype(M))
+        # since the zero would need to be evaluated from the elements,
+        # we copy the array to avoid undefined references in triu!
+        copy!(d, M)
+    end
     A = triu!(d,k)
     if iszero(k)
         copytrito!(A, M, 'U')
@@ -509,6 +514,11 @@ julia> tril(a,-3)
 """
 function tril(M::AbstractMatrix,k::Integer=0)
     d = similar(M)
+    if !haszero(eltype(M))
+        # since the zero would need to be evaluated from the elements,
+        # we copy the array to avoid undefined references in tril!
+        copy!(d, M)
+    end
     A = tril!(d,k)
     if iszero(k)
         copytrito!(A, M, 'L')

test/diagonal.jl

@@ -819,6 +819,13 @@ end
         @test all(x -> size(x) == (2,2), D)
         @test D == D1 * D2
     end
+
+    @testset "triu/tril" begin
+        D = Diagonal(fill(ones(2,2), 3))
+        M = Matrix{eltype(D)}(D)
+        @test triu(D,1) == triu(M,1)
+        @test tril(D,-1) == tril(M,-1)
+    end
 end
 
 @testset "Eigensystem for block diagonal (issue #30681)" begin