From 7a54d3df317529307e0ac10be0e69027e944ea4c Mon Sep 17 00:00:00 2001
From: Sacha Verweij <sacha@stanford.edu>
Date: Mon, 30 Oct 2017 16:29:18 -0700
Subject: [PATCH 1/2] Add Diagonal[{T}](S::UniformScaling, n) constructors.

---
 base/linalg/uniformscaling.jl | 4 ++++
 test/linalg/uniformscaling.jl | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/base/linalg/uniformscaling.jl b/base/linalg/uniformscaling.jl
index cd0afb23567d7..4060fcc3e533b 100644
--- a/base/linalg/uniformscaling.jl
+++ b/base/linalg/uniformscaling.jl
@@ -381,3 +381,7 @@ Matrix(s::UniformScaling, dims::Dims{2}) = Matrix{eltype(s)}(s, dims)
 # convenience variations that accept a single integer to specify dims
 Matrix{T}(s::UniformScaling, m::Integer) where {T} = Matrix{T}(s, m, m)
 Matrix(s::UniformScaling, m::Integer) = Matrix(s, m, m)
+
+## Diagonal construction from UniformScaling
+Diagonal{T}(s::UniformScaling, m::Integer) where {T} = Diagonal{T}(fill(T(s.λ), m))
+Diagonal(s::UniformScaling, m::Integer) = Diagonal{eltype(s)}(s, m)
diff --git a/test/linalg/uniformscaling.jl b/test/linalg/uniformscaling.jl
index 4541b274e5614..c506f7c7ef5e7 100644
--- a/test/linalg/uniformscaling.jl
+++ b/test/linalg/uniformscaling.jl
@@ -201,6 +201,13 @@ end
     @test Matrix{Float64}(2I, 3, 3)::Matrix{Float64} == 2*eye(3)
 end
 
+@testset "Diagonal construction from UniformScaling" begin
+    @test Diagonal(2I, 3)::Diagonal{Int} == 2*eye(3)
+    @test Diagonal(2.0I, 3)::Diagonal{Float64} == 2*eye(3)
+    @test Diagonal{Real}(2I, 3)::Diagonal{Real} == 2*eye(3)
+    @test Diagonal{Float64}(2I, 3)::Diagonal{Float64} == 2*eye(3)
+end
+
 @testset "equality comparison of matrices with UniformScaling" begin
     # AbstractMatrix methods
     diagI = Diagonal(fill(1, 3))

From 3fa96bdadfa5cf7f5b4d0d914af50baf7486228f Mon Sep 17 00:00:00 2001
From: Sacha Verweij <sacha@stanford.edu>
Date: Mon, 30 Oct 2017 16:33:28 -0700
Subject: [PATCH 2/2] Deprecate eye(::Type{Diagonal{T}}, m::Integer) method.

---
 NEWS.md                 | 3 +++
 base/deprecated.jl      | 2 ++
 base/linalg/diagonal.jl | 2 --
 test/linalg/diagonal.jl | 1 -
 4 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index d2e14b873ed5c..cd90627d8f354 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -305,6 +305,9 @@ Library improvements
 
   * The `crc32c` function for CRC-32c checksums is now exported ([#22274]).
 
+  * `eye(::Type{Diagonal{T}}, m::Integer)` has been deprecated in favor of
+    `Diagonal{T}(I, m)` ([#24413]).
+
   * The output of `versioninfo` is now controlled with keyword arguments ([#21974]).
 
   * The function `LibGit2.set_remote_url` now always sets both the fetch and push URLs for a
diff --git a/base/deprecated.jl b/base/deprecated.jl
index 1582e8bb8df37..c6a6561a3304c 100644
--- a/base/deprecated.jl
+++ b/base/deprecated.jl
@@ -1786,6 +1786,8 @@ end
     @deprecate get_creds!(cache::CachedCredentials, credid, default) get!(cache, credid, default)
 end
 
+@deprecate eye(::Type{Diagonal{T}}, n::Int) where {T} Diagonal{T}(I, n)
+
 export tic, toq, toc
 function tic()
     depwarn("tic() is deprecated, use @time, @elapsed, or calls to time_ns() instead.", :tic)
diff --git a/base/linalg/diagonal.jl b/base/linalg/diagonal.jl
index 93533a4b02f64..a655516456878 100644
--- a/base/linalg/diagonal.jl
+++ b/base/linalg/diagonal.jl
@@ -341,8 +341,6 @@ function logdet(D::Diagonal{<:Complex}) # make sure branch cut is correct
     z = sum(log, D.diag)
     complex(real(z), rem2pi(imag(z), RoundNearest))
 end
-# identity matrices via eye(Diagonal{type},n)
-eye(::Type{Diagonal{T}}, n::Int) where {T} = Diagonal(ones(T,n))
 
 # Matrix functions
 for f in (:exp, :log, :sqrt,
diff --git a/test/linalg/diagonal.jl b/test/linalg/diagonal.jl
index d57807c9eaf6c..5319efd7a8742 100644
--- a/test/linalg/diagonal.jl
+++ b/test/linalg/diagonal.jl
@@ -29,7 +29,6 @@ srand(1)
     end
 
     @testset "Basic properties" begin
-        @test eye(Diagonal{elty},n) == Diagonal(ones(elty,n))
         @test_throws ArgumentError size(D,0)
         @test typeof(convert(Diagonal{Complex64},D)) <: Diagonal{Complex64}
         @test typeof(convert(AbstractMatrix{Complex64},D)) <: Diagonal{Complex64}