From ca95b73ba192cc9952b1c36f7de6ac5691df89d0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20Legat?= <benoit.legat@gmail.com>
Date: Tue, 5 May 2020 12:29:52 +0200
Subject: [PATCH] Fix diagm_container for types without zero

---
 stdlib/LinearAlgebra/src/dense.jl  |  4 +++-
 stdlib/LinearAlgebra/test/dense.jl | 11 +++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/stdlib/LinearAlgebra/src/dense.jl b/stdlib/LinearAlgebra/src/dense.jl
index cf6af00481060..7e5eb8e9cdd8a 100644
--- a/stdlib/LinearAlgebra/src/dense.jl
+++ b/stdlib/LinearAlgebra/src/dense.jl
@@ -301,7 +301,9 @@ function diagm_size(size::Tuple{Int,Int}, kv::Pair{<:Integer,<:AbstractVector}..
 end
 function diagm_container(size, kv::Pair{<:Integer,<:AbstractVector}...)
     T = promote_type(map(x -> eltype(x.second), kv)...)
-    return zeros(T, diagm_size(size, kv...)...)
+    # For some type `T`, `zero(T)` is not a `T` and `zeros(T, ...)` fails.
+    U = promote_type(T, typeof(zero(T)))
+    return zeros(U, diagm_size(size, kv...)...)
 end
 diagm_container(size, kv::Pair{<:Integer,<:BitVector}...) =
     falses(diagm_size(size, kv...)...)
diff --git a/stdlib/LinearAlgebra/test/dense.jl b/stdlib/LinearAlgebra/test/dense.jl
index 3305a9284343b..bcba570946163 100644
--- a/stdlib/LinearAlgebra/test/dense.jl
+++ b/stdlib/LinearAlgebra/test/dense.jl
@@ -928,4 +928,15 @@ end
     @test exp(log(A2)) ≈ A2
 end
 
+struct TypeWithoutZero end
+Base.zero(::Type{TypeWithoutZero}) = TypeWithZero()
+struct TypeWithZero end
+Base.promote_rule(::Type{TypeWithoutZero}, ::Type{TypeWithZero}) = TypeWithZero
+Base.zero(::Type{<:Union{TypeWithoutZero, TypeWithZero}}) = TypeWithZero()
+Base.:+(x::TypeWithZero, ::TypeWithoutZero) = x
+
+@testset "diagm for type with no zero" begin
+    @test diagm(0 => [TypeWithoutZero()]) isa Matrix{TypeWithZero}
+end
+
 end # module TestDense