Fix diagm_container for types without zero (#35743)

JuliaLang · Jun 11, 2020 · a3ef188 · a3ef188
1 parent f0b369c
commit a3ef188
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diff --git 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
@@ -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