[WIP] Fall back to 'sort.Slice' on Go 1.7 where 'sort.SliceStable' does not exist

gps/constraint.go

@@ -6,7 +6,6 @@ package gps
 
 import (
 	"fmt"
-	"sort"
 
 	"github.com/Masterminds/semver"
 	"github.com/golang/dep/gps/internal/pb"
@@ -375,7 +374,7 @@ func (m ProjectConstraints) overrideAll(pcm ProjectConstraints) (out []workingCo
 		k++
 	}
 
-	sort.SliceStable(out, func(i, j int) bool {
+	sortSlice(out, func(i, j int) bool {
 		return out[i].Ident.Less(out[j].Ident)
 	})
 	return

gps/lock_test.go

@@ -6,7 +6,6 @@ package gps
 
 import (
 	"reflect"
-	"sort"
 	"testing"
 )
 
@@ -21,7 +20,7 @@ func TestLockedProjectSorting(t *testing.T) {
 	lps2 := make([]LockedProject, len(lps))
 	copy(lps2, lps)
 
-	sort.SliceStable(lps2, func(i, j int) bool {
+	sortSlice(lps2, func(i, j int) bool {
 		return lps2[i].Ident().Less(lps2[j].Ident())
 	})
 

gps/sort_go_1_8.go

@@ -0,0 +1,13 @@
+// Copyright 2018 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
+
+package gps
+
+import "sort"
+
+func sortSlice(slice interface{}, less func(i, j int) bool) {
+	sort.SliceStable(slice, less)
+}

gps/sort_pre_go_1_8.go

@@ -0,0 +1,13 @@
+// Copyright 2018 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
+
+package gps
+
+import "sort"
+
+func sortSlice(slice interface{}, less func(i, j int) bool) {
+	sort.Slice(slice, less)
+}