feat(Between): handles value implementing Compare & Less methods

as well as Gt, Gte, Lt and Lte of course.

Compare and/or Less methods signatures follow:
  func (a T) Less(b T) bool   // returns true if a < b
  func (a T) Compare(b T) int // returns -1 if a < b, 1 if a > b, 0 if a == b

Additional Between, Gt, Gte, Lt and Lte changes:
- failure reports display numbers as elsewhere;
- docs fixed.

Signed-off-by: Maxime Soulé <btik-git@scoubidou.com>

Author: maxatome

internal/types/order.go

@@ -0,0 +1,64 @@
+// Copyright (c) 2021-2022, Maxime Soulé
+// All rights reserved.
+//
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree.
+
+package types
+
+import (
+	"reflect"
+
+	"github.com/maxatome/go-testdeep/internal/dark"
+)
+
+// NewOrder returns a function able to compare 2 non-nil values of type "t".
+// It returns nil if the type "t" is not comparable.
+func NewOrder(t reflect.Type) func(a, b reflect.Value) int {
+	// Compare(T) int
+	if m, ok := cmpMethod("Compare", t, Int); ok {
+		return func(va, vb reflect.Value) int {
+			// use dark.MustGetInterface() to bypass possible private fields
+			ret := m.Call([]reflect.Value{
+				reflect.ValueOf(dark.MustGetInterface(va)),
+				reflect.ValueOf(dark.MustGetInterface(vb)),
+			})
+			return int(ret[0].Int())
+		}
+	}
+
+	// Less(T) bool
+	if m, ok := cmpMethod("Less", t, Bool); ok {
+		return func(va, vb reflect.Value) int {
+			// use dark.MustGetInterface() to bypass possible private fields
+			va = reflect.ValueOf(dark.MustGetInterface(va))
+			vb = reflect.ValueOf(dark.MustGetInterface(vb))
+			ret := m.Call([]reflect.Value{va, vb})
+			if ret[0].Bool() { // a < b
+				return -1
+			}
+			ret = m.Call([]reflect.Value{vb, va})
+			if ret[0].Bool() { // b < a
+				return 1
+			}
+			return 0
+		}
+	}
+
+	return nil
+}
+
+func cmpMethod(name string, in, out reflect.Type) (reflect.Value, bool) {
+	if equal, ok := in.MethodByName(name); ok {
+		ft := equal.Type
+		if !ft.IsVariadic() &&
+			ft.NumIn() == 2 &&
+			ft.NumOut() == 1 &&
+			ft.In(0) == in &&
+			ft.In(1) == in &&
+			ft.Out(0) == out {
+			return equal.Func, true
+		}
+	}
+	return reflect.Value{}, false
+}

internal/types/order_test.go

@@ -0,0 +1,92 @@
+// Copyright (c) 2022, Maxime Soulé
+// All rights reserved.
+//
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree.
+
+package types_test
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/maxatome/go-testdeep/internal/test"
+	"github.com/maxatome/go-testdeep/internal/types"
+)
+
+type compareType int
+
+func (i compareType) Compare(j compareType) int {
+	if i < j {
+		return -1
+	}
+	if i > j {
+		return 1
+	}
+	return 0
+}
+
+type lessType int
+
+func (i lessType) Less(j lessType) bool {
+	return i < j
+}
+
+type badType1 int
+
+func (i badType1) Compare(j ...badType1) int { return 0 }     // IsVariadic()
+func (i badType1) Less(j, k badType1) bool   { return false } // NumIn() == 3
+
+type badType2 int
+
+func (i badType2) Compare() int    { return 0 } // NumIn() == 1
+func (i badType2) Less(j badType2) {}           // NumOut() == 0
+
+type badType3 int
+
+func (i badType3) Compare(j badType3) (int, int) { return 0, 0 }  // NumOut() == 2
+func (i badType3) Less(j int) bool               { return false } // In(1) ≠ in
+
+type badType4 int
+
+func (i badType4) Compare(j badType4) bool { return false } // Out(0) ≠ out
+func (i badType4) Less(j badType4) int     { return 0 }     // Out(0) ≠ out
+
+func TestOrder(t *testing.T) {
+	if types.NewOrder(reflect.TypeOf(0)) != nil {
+		t.Error("types.NewOrder(int) returned non-nil func")
+	}
+
+	fn := types.NewOrder(reflect.TypeOf(compareType(0)))
+	if fn == nil {
+		t.Error("types.NewOrder(compareType) returned nil func")
+	} else {
+		a, b := reflect.ValueOf(compareType(1)), reflect.ValueOf(compareType(2))
+		test.EqualInt(t, fn(a, b), -1)
+		test.EqualInt(t, fn(b, a), 1)
+		test.EqualInt(t, fn(a, a), 0)
+	}
+
+	fn = types.NewOrder(reflect.TypeOf(lessType(0)))
+	if fn == nil {
+		t.Error("types.NewOrder(lessType) returned nil func")
+	} else {
+		a, b := reflect.ValueOf(lessType(1)), reflect.ValueOf(lessType(2))
+		test.EqualInt(t, fn(a, b), -1)
+		test.EqualInt(t, fn(b, a), 1)
+		test.EqualInt(t, fn(a, a), 0)
+	}
+
+	if types.NewOrder(reflect.TypeOf(badType1(0))) != nil {
+		t.Error("types.NewOrder(badType1) returned non-nil func")
+	}
+	if types.NewOrder(reflect.TypeOf(badType2(0))) != nil {
+		t.Error("types.NewOrder(badType2) returned non-nil func")
+	}
+	if types.NewOrder(reflect.TypeOf(badType3(0))) != nil {
+		t.Error("types.NewOrder(badType3) returned non-nil func")
+	}
+	if types.NewOrder(reflect.TypeOf(badType4(0))) != nil {
+		t.Error("types.NewOrder(badType4) returned non-nil func")
+	}
+}