util.SortMounts(): make the returned order more stable

Use sort.Stable() instead of sort.Sort() to sort mounts, and have the
comparison function compare the cleaned paths directly if they have the
same number of components, so that there's a defined ordering between
"/a" and "/b".

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

util/util.go

@@ -441,7 +441,14 @@ func (m byDestination) Len() int {
 }
 
 func (m byDestination) Less(i, j int) bool {
-	return m.parts(i) < m.parts(j)
+	iparts, jparts := m.parts(i), m.parts(j)
+	switch {
+	case iparts < jparts:
+		return true
+	case iparts > jparts:
+		return false
+	}
+	return filepath.Clean(m[i].Destination) < filepath.Clean(m[j].Destination)
 }
 
 func (m byDestination) Swap(i, j int) {
@@ -453,7 +460,7 @@ func (m byDestination) parts(i int) int {
 }
 
 func SortMounts(m []specs.Mount) []specs.Mount {
-	sort.Sort(byDestination(m))
+	sort.Stable(byDestination(m))
 	return m
 }
 

util/util_test.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/containers/common/pkg/config"
 	specs "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/stretchr/testify/assert"
 )
 
 func TestMergeEnv(t *testing.T) {
@@ -93,45 +94,20 @@ func TestMountsSort(t *testing.T) {
 			Destination: "/aa/b/c",
 		},
 	}
-	mounts1b := []specs.Mount{
-		{
-			Source:      "/xyz",
-			Destination: "/",
-		},
-		{
-			Source:      "/a",
-			Destination: "/a",
-		},
-		{
-			Source:      "/b",
-			Destination: "/b",
-		},
-		{
-			Source:      "/a/b",
-			Destination: "/a/b",
-		},
-		{
-			Source:      "/d/e",
-			Destination: "/a/c",
-		},
-		{
-			Source:      "/a/b/c",
-			Destination: "/a/b/c",
-		},
-		{
-			Source:      "/a/bb/c",
-			Destination: "/a/bb/c",
-		},
-		{
-			Source:      "/a/b/c",
-			Destination: "/aa/b/c",
-		},
+	mounts1b := []string{
+		"/",
+		"/a",
+		"/b",
+		"/a/b",
+		"/a/c",
+		"/a/b/c",
+		"/a/bb/c",
+		"/aa/b/c",
 	}
 	sorted := SortMounts(mounts1a)
+	sortedDests := make([]string, len(mounts1a))
 	for i := range sorted {
-		if sorted[i].Destination != mounts1b[i].Destination {
-			t.Fatalf("failed sort \n%+v\n%+v", mounts1b, sorted)
-		}
+		sortedDests[i] = sorted[i].Destination
 	}
-
+	assert.Equalf(t, mounts1b, sortedDests, "sort returned results in unexpected by-destination order")
 }