From a3ef188430c7b9726cc7e90f36011d2f31c9e064 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20Legat?= <benoit.legat@gmail.com>
Date: Thu, 11 Jun 2020 16:41:08 +0200
Subject: [PATCH] Fix diagm_container for types without zero (#35743)

---
 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 8a57a1eaf52cf..4ea27e26bc7b8 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 1c7eeb5b4acac..2dec8e95402d7 100644
--- a/stdlib/LinearAlgebra/test/dense.jl
+++ b/stdlib/LinearAlgebra/test/dense.jl
@@ -939,4 +939,15 @@ 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