Fix sorting bugs (esp MissingOptimization) that come up when using …

…SortingAlgorithms.TimSort (#50171)

(cherry picked from commit ba251e8)

base/sort.jl

@@ -43,6 +43,7 @@ export # not exported by Base
     SMALL_ALGORITHM,
     SMALL_THRESHOLD
 
+abstract type Algorithm end
 
 ## functions requiring only ordering ##
 
@@ -420,7 +421,7 @@ for (sym, exp, type) in [
         (:mn, :(throw(ArgumentError("mn is needed but has not been computed"))), :(eltype(v))),
         (:mx, :(throw(ArgumentError("mx is needed but has not been computed"))), :(eltype(v))),
         (:scratch, nothing, :(Union{Nothing, Vector})), # could have different eltype
-        (:allow_legacy_dispatch, true, Bool)]
+        (:legacy_dispatch_entry, nothing, Union{Nothing, Algorithm})]
     usym = Symbol(:_, sym)
     @eval function $usym(v, o, kw)
         # using missing instead of nothing because scratch could === nothing.
@@ -483,8 +484,6 @@ internal or recursive calls.
 """
 function _sort! end
 
-abstract type Algorithm end
-
 
 """
     MissingOptimization(next) <: Algorithm
@@ -508,12 +507,12 @@ struct WithoutMissingVector{T, U} <: AbstractVector{T}
         new{nonmissingtype(eltype(data)), typeof(data)}(data)
     end
 end
-Base.@propagate_inbounds function Base.getindex(v::WithoutMissingVector, i)
+Base.@propagate_inbounds function Base.getindex(v::WithoutMissingVector, i::Integer)
     out = v.data[i]
     @assert !(out isa Missing)
     out::eltype(v)
 end
-Base.@propagate_inbounds function Base.setindex!(v::WithoutMissingVector, x, i)
+Base.@propagate_inbounds function Base.setindex!(v::WithoutMissingVector, x, i::Integer)
     v.data[i] = x
     v
 end
@@ -574,8 +573,10 @@ function _sort!(v::AbstractVector, a::MissingOptimization, o::Ordering, kw)
         # we can assume v is equal to eachindex(o.data) which allows a copying partition
         # without allocations.
         lo_i, hi_i = lo, hi
-        for (i,x) in zip(eachindex(o.data), o.data)
-            if ismissing(x) == (o.order == Reverse) # should i go at the beginning?
+        cv = eachindex(o.data) # equal to copy(v)
+        for i in lo:hi
+            x = o.data[cv[i]]
+            if ismissing(x) == (o.order == Reverse) # should x go at the beginning/end?
                 v[lo_i] = i
                 lo_i += 1
             else
@@ -2119,25 +2120,25 @@ end
 # Support 3-, 5-, and 6-argument versions of sort! for calling into the internals in the old way
 sort!(v::AbstractVector, a::Algorithm, o::Ordering) = sort!(v, firstindex(v), lastindex(v), a, o)
 function sort!(v::AbstractVector, lo::Integer, hi::Integer, a::Algorithm, o::Ordering)
-    _sort!(v, a, o, (; lo, hi, allow_legacy_dispatch=false))
+    _sort!(v, a, o, (; lo, hi, legacy_dispatch_entry=a))
     v
 end
 sort!(v::AbstractVector, lo::Integer, hi::Integer, a::Algorithm, o::Ordering, _) = sort!(v, lo, hi, a, o)
 function sort!(v::AbstractVector, lo::Integer, hi::Integer, a::Algorithm, o::Ordering, scratch::Vector)
-    _sort!(v, a, o, (; lo, hi, scratch, allow_legacy_dispatch=false))
+    _sort!(v, a, o, (; lo, hi, scratch, legacy_dispatch_entry=a))
     v
 end
 
 # Support dispatch on custom algorithms in the old way
 # sort!(::AbstractVector, ::Integer, ::Integer, ::MyCustomAlgorithm, ::Ordering) = ...
 function _sort!(v::AbstractVector, a::Algorithm, o::Ordering, kw)
-    @getkw lo hi scratch allow_legacy_dispatch
-    if allow_legacy_dispatch
+    @getkw lo hi scratch legacy_dispatch_entry
+    if legacy_dispatch_entry === a
+        # This error prevents infinite recursion for unknown algorithms
+        throw(ArgumentError("Base.Sort._sort!(::$(typeof(v)), ::$(typeof(a)), ::$(typeof(o)), ::Any) is not defined"))
+    else
         sort!(v, lo, hi, a, o)
         scratch
-    else
-        # This error prevents infinite recursion for unknown algorithms
-        throw(ArgumentError("Base.Sort._sort!(::$(typeof(v)), ::$(typeof(a)), ::$(typeof(o))) is not defined"))
     end
 end
 

test/sorting.jl

@@ -955,6 +955,46 @@ end
     test_allocs()
 end
 
+@testset "MissingOptimization fastpath for Perm ordering when lo:hi ≠ eachindex(v)" begin
+    v = [rand() < .5 ? missing : rand() for _ in 1:100]
+    ix = collect(1:100)
+    sort!(ix, 1, 10, Base.Sort.DEFAULT_STABLE, Base.Order.Perm(Base.Order.Forward, v))
+    @test issorted(v[ix[1:10]])
+end
+
+struct NonScalarIndexingOfWithoutMissingVectorAlg <: Base.Sort.Algorithm end
+function Base.Sort._sort!(v::AbstractVector, ::NonScalarIndexingOfWithoutMissingVectorAlg, o::Base.Order.Ordering, kw)
+    Base.Sort.@getkw lo hi
+    first_half = v[lo:lo+(hi-lo)÷2]
+    second_half = v[lo+(hi-lo)÷2+1:hi]
+    whole = v[lo:hi]
+    all(vcat(first_half, second_half) .=== whole) || error()
+    out = Base.Sort._sort!(whole, Base.Sort.DEFAULT_STABLE, o, (;kw..., lo=1, hi=length(whole)))
+    v[lo:hi] .= whole
+    out
+end
+
+@testset "Non-scaler indexing of WithoutMissingVector" begin
+    @testset "Unit test" begin
+        wmv = Base.Sort.WithoutMissingVector(Union{Missing, Int}[1, 7, 2, 9])
+        @test wmv[[1, 3]] == [1, 2]
+        @test wmv[1:3] == [1, 7, 2]
+    end
+    @testset "End to end" begin
+        alg = Base.Sort.InitialOptimizations(NonScalarIndexingOfWithoutMissingVectorAlg())
+        @test issorted(sort(rand(100); alg))
+        @test issorted(sort([rand() < .5 ? missing : randstring() for _ in 1:100]; alg))
+    end
+end
+
+struct DispatchLoopTestAlg <: Base.Sort.Algorithm end
+function Base.sort!(v::AbstractVector, lo::Integer, hi::Integer, ::DispatchLoopTestAlg, order::Base.Order.Ordering)
+    sort!(view(v, lo:hi); order)
+end
+@testset "Support dispatch from the old style to the new style and back" begin
+    @test issorted(sort!(rand(100), Base.Sort.InitialOptimizations(DispatchLoopTestAlg()), Base.Order.Forward))
+end
+
 # This testset is at the end of the file because it is slow.
 @testset "searchsorted" begin
     numTypes = [ Int8,  Int16,  Int32,  Int64,  Int128,