Support missing in coalesce()

base/missing.jl

@@ -33,7 +33,6 @@ promote_rule(::Type{Missing}, ::Type{Missing}) = Missing
 convert(::Type{Union{T, Missing}}, x) where {T} = convert(T, x)
 # To fix ambiguities
 convert(::Type{Missing}, ::Missing) = missing
-convert(::Type{Void}, ::Void) = nothing
 convert(::Type{Union{Void, Missing}}, x::Union{Void, Missing}) = x
 convert(::Type{Union{Void, Missing}}, x) =
     throw(MethodError(convert, (Union{Void, Missing}, x)))

base/some.jl

@@ -35,16 +35,19 @@ end
 """
     coalesce(x, y...)
 
-Return the first value in the arguments which is not equal to `nothing`,
-or `nothing` if all arguments are `nothing`. Unwrap arguments of type
-[`Some`](@ref).
+Return the first value in the arguments which is not equal to
+either [`nothing`](@ref) or [`missing`](@ref), or the last argument.
+Unwrap arguments of type [`Some`](@ref).
 
 # Examples
 
 ```jldoctest
 julia> coalesce(nothing, 1)
 1
 
+julia> coalesce(missing, 1)
+1
+
 julia> coalesce(1, nothing)
 1
 
@@ -63,9 +66,10 @@ function coalesce end
 coalesce(x::Any) = x
 coalesce(x::Some) = x.value
 coalesce(x::Void) = nothing
+coalesce(x::Missing) = missing
 coalesce(x::Any, y...) = x
 coalesce(x::Some, y...) = x.value
-coalesce(x::Void, y...) = coalesce(y...)
+coalesce(x::Union{Void, Missing}, y...) = coalesce(y...)
 
 """
     notnothing(x)

test/some.jl

@@ -49,26 +49,33 @@
 
 # coalesce()
 
-@test coalesce(1) === 1
-@test coalesce(nothing) === nothing
-@test coalesce(nothing, 1) === 1
-@test coalesce(1, nothing) === 1
-@test coalesce(nothing, nothing) === nothing
-@test coalesce(nothing, 1, 2) === 1
-@test coalesce(1, nothing, 2) === 1
-@test coalesce(nothing, nothing, 2) === 2
-@test coalesce(nothing, nothing, nothing) === nothing
-
-@test coalesce(Some(1)) === 1
-@test coalesce(Some(nothing)) === nothing
-@test coalesce(Some(1), 0) === 1
-@test coalesce(Some(nothing), 0) === nothing
-@test coalesce(nothing, Some(nothing)) === nothing
-@test coalesce(Some(1), nothing) === 1
-@test coalesce(nothing, Some(1)) === 1
-@test coalesce(nothing, Some(1), nothing) === 1
-@test coalesce(nothing, Some(1), Some(2)) === 1
-@test coalesce(Some(1), nothing, Some(2)) === 1
+for v in (nothing, missing)
+    @test coalesce(1) === 1
+    @test coalesce(v) === v
+    @test coalesce(v, 1) === 1
+    @test coalesce(1, v) === 1
+    @test coalesce(v, v) === v
+    @test coalesce(v, 1, 2) === 1
+    @test coalesce(1, v, 2) === 1
+    @test coalesce(v, v, 2) === 2
+    @test coalesce(v, v, v) === v
+
+    @test coalesce(Some(1)) === 1
+    @test coalesce(Some(v)) === v
+    @test coalesce(Some(1), 0) === 1
+    @test coalesce(Some(v), 0) === v
+    @test coalesce(v, Some(v)) === v
+    @test coalesce(Some(1), v) === 1
+    @test coalesce(v, Some(1)) === 1
+    @test coalesce(v, Some(1), v) === 1
+    @test coalesce(v, Some(1), Some(2)) === 1
+    @test coalesce(Some(1), v, Some(2)) === 1
+
+    @test coalesce(v, missing) === missing
+    @test coalesce(v, nothing) === nothing
+    @test coalesce(v, missing, v) === v
+    @test coalesce(v, nothing, v) === v
+end
 
 # notnothing()