sort, internal/reflectlite: flesh out reflectlite enough for use by sort

Now the net package is back to no longer depending on unicode. And lock that in
with a test.

Fixes #30440

Change-Id: I18b89b02f7d96488783adc07308da990f505affd
Reviewed-on: https://go-review.googlesource.com/c/go/+/169137
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 55 insertions, 7 deletions

diff --git a/src/sort/slice.go b/src/sort/slice.go
index 206f12173d..5196affcfd 100644
--- a/src/sort/slice.go
+++ b/src/sort/slice.go
@@ -2,11 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !compiler_bootstrap go1.8
+// +build !compiler_bootstrap go1.13
 
 package sort
 
-import "reflect"
+import (
+	"internal/reflectlite"
+)
 
 // Slice sorts the provided slice given the provided less function.
 //
@@ -15,8 +17,8 @@ import "reflect"
 //
 // The function panics if the provided interface is not a slice.
 func Slice(slice interface{}, less func(i, j int) bool) {
-	rv := reflect.ValueOf(slice)
-	swap := reflect.Swapper(slice)
+	rv := reflectlite.ValueOf(slice)
+	swap := reflectlite.Swapper(slice)
 	length := rv.Len()
 	quickSort_func(lessSwap{less, swap}, 0, length, maxDepth(length))
 }
@@ -26,8 +28,8 @@ func Slice(slice interface{}, less func(i, j int) bool) {
 //
 // The function panics if the provided interface is not a slice.
 func SliceStable(slice interface{}, less func(i, j int) bool) {
-	rv := reflect.ValueOf(slice)
-	swap := reflect.Swapper(slice)
+	rv := reflectlite.ValueOf(slice)
+	swap := reflectlite.Swapper(slice)
 	stable_func(lessSwap{less, swap}, rv.Len())
 }
 
@@ -35,7 +37,7 @@ func SliceStable(slice interface{}, less func(i, j int) bool) {
 //
 // The function panics if the provided interface is not a slice.
 func SliceIsSorted(slice interface{}, less func(i, j int) bool) bool {
-	rv := reflect.ValueOf(slice)
+	rv := reflectlite.ValueOf(slice)
 	n := rv.Len()
 	for i := n - 1; i > 0; i-- {
 		if less(i, i-1) {
diff --git a/src/sort/slice_pre113.go b/src/sort/slice_pre113.go
new file mode 100644
index 0000000000..4d5f759a92
--- /dev/null
+++ b/src/sort/slice_pre113.go
@@ -0,0 +1,46 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.8,!go1.13
+
+package sort
+
+import "reflect"
+
+// Slice sorts the provided slice given the provided less function.
+//
+// The sort is not guaranteed to be stable. For a stable sort, use
+// SliceStable.
+//
+// The function panics if the provided interface is not a slice.
+func Slice(slice interface{}, less func(i, j int) bool) {
+	rv := reflect.ValueOf(slice)
+	swap := reflect.Swapper(slice)
+	length := rv.Len()
+	quickSort_func(lessSwap{less, swap}, 0, length, maxDepth(length))
+}
+
+// SliceStable sorts the provided slice given the provided less
+// function while keeping the original order of equal elements.
+//
+// The function panics if the provided interface is not a slice.
+func SliceStable(slice interface{}, less func(i, j int) bool) {
+	rv := reflect.ValueOf(slice)
+	swap := reflect.Swapper(slice)
+	stable_func(lessSwap{less, swap}, rv.Len())
+}
+
+// SliceIsSorted tests whether a slice is sorted.
+//
+// The function panics if the provided interface is not a slice.
+func SliceIsSorted(slice interface{}, less func(i, j int) bool) bool {
+	rv := reflect.ValueOf(slice)
+	n := rv.Len()
+	for i := n - 1; i > 0; i-- {
+		if less(i, i-1) {
+			return false
+		}
+	}
+	return true
+}