min, max, minmax use isless for comparison (fix #23094) (#23155)

base/array.jl

@@ -1697,7 +1697,7 @@ end
 
 Returns the maximum element of the collection `itr` and its index. If there are multiple
 maximal elements, then the first one will be returned. `NaN` values are ignored, unless
-all elements are `NaN`.
+all elements are `NaN`. Other than the treatment of `NaN`, the result is in line with `max`.
 
 The collection must not be empty.
 
@@ -1723,7 +1723,8 @@ function findmax(a)
     while !done(a, s)
         ai, s = next(a, s)
         i += 1
-        if ai > m || m!=m
+        ai != ai && continue # assume x != x => x is a NaN
+        if m != m || isless(m, ai)
             m = ai
             mi = i
         end
@@ -1736,7 +1737,7 @@ end
 
 Returns the minimum element of the collection `itr` and its index. If there are multiple
 minimal elements, then the first one will be returned. `NaN` values are ignored, unless
-all elements are `NaN`.
+all elements are `NaN`. Other than the treatment of `NaN`, the result is in line with `min`.
 
 The collection must not be empty.
 
@@ -1762,7 +1763,8 @@ function findmin(a)
     while !done(a, s)
         ai, s = next(a, s)
         i += 1
-        if ai < m || m!=m
+        ai != ai && continue
+        if m != m || isless(ai, m)
             m = ai
             mi = i
         end

base/operators.jl

@@ -359,7 +359,7 @@ julia> max(2, 5, 1)
 5
 ```
 """
-max(x, y) = ifelse(y < x, x, y)
+max(x, y) = ifelse(isless(y, x), x, y)
 
 """
     min(x, y, ...)
@@ -373,7 +373,7 @@ julia> min(2, 5, 1)
 1
 ```
 """
-min(x,y) = ifelse(y < x, y, x)
+min(x,y) = ifelse(isless(y, x), y, x)
 
 """
     minmax(x, y)
@@ -386,7 +386,7 @@ julia> minmax('c','b')
 ('b', 'c')
 ```
 """
-minmax(x,y) = y < x ? (y, x) : (x, y)
+minmax(x,y) = isless(y, x) ? (y, x) : (x, y)
 
 scalarmax(x,y) = max(x,y)
 scalarmax(x::AbstractArray, y::AbstractArray) = throw(ArgumentError("ordering is not well-defined for arrays"))

test/arrayops.jl

@@ -495,6 +495,20 @@ end
     @test indmax(5:-2:1) == 1
     @test findmin(5:-2:1) == (1,3)
     @test indmin(5:-2:1) == 3
+
+    #23094
+    @test findmax(Set(["abc"])) === ("abc", 1)
+    @test findmin(["abc", "a"]) === ("a", 2)
+    @test_throws MethodError findmax([Set([1]), Set([2])])
+    @test findmin([0.0, -0.0]) === (-0.0, 2)
+    @test findmax([0.0, -0.0]) === (0.0, 1)
+    @test findmin([-0.0, 0.0]) === (-0.0, 1)
+    @test findmax([-0.0, 0.0]) === (0.0, 2)
+    @test isnan(findmin([NaN, NaN, 0.0/0.0])[1])
+    @test findmin([NaN, NaN, 0.0/0.0])[2] == 1
+    @test isnan(findmax([NaN, NaN, 0.0/0.0])[1])
+    @test findmax([NaN, NaN, 0.0/0.0])[2] == 1
+
 end
 
 @testset "permutedims" begin

test/operators.jl

@@ -58,6 +58,29 @@ p = 1=>:foo
 @test_throws ArgumentError Base.scalarmax('a',['c','d'])
 @test_throws ArgumentError Base.scalarmax(['a','b'],'c')
 
+@test_throws MethodError min(Set([1]), Set([2]))
+@test_throws MethodError max(Set([1]), Set([2]))
+@test_throws MethodError minmax(Set([1]), Set([2]))
+
+# Test if isless (not <) is used by min, max, minmax
+# and commutativity.
+struct TO23094
+    x::Int
+end
+Base.isless(a::TO23094, b::TO23094) = isless(a.x, b.x)
+Base.isequal(a::TO23094, b::TO23094) = isequal(a.x, b.x)
+import Base.<
+<(a::TO23094, b::TO23094) = error("< should not be called")
+
+@test isequal(min(TO23094(1), TO23094(2)), TO23094(1))
+@test isequal(min(TO23094(2), TO23094(1)), TO23094(1))
+@test isequal(max(TO23094(1), TO23094(2)), TO23094(2))
+@test isequal(max(TO23094(2), TO23094(1)), TO23094(2))
+@test isequal(minmax(TO23094(1), TO23094(2))[1], TO23094(1))
+@test isequal(minmax(TO23094(1), TO23094(2))[2], TO23094(2))
+@test isequal(minmax(TO23094(2), TO23094(1))[1], TO23094(1))
+@test isequal(minmax(TO23094(2), TO23094(1))[2], TO23094(2))
+
 @test lexless('a','b')
 
 @test 1 .!= 2