@@ -24,6 +24,7 @@ import (

 	"github.com/docker/docker/internal/test/fakestorage"

 	"github.com/docker/docker/internal/testutil"

 	"github.com/docker/docker/pkg/archive"

+	"github.com/docker/docker/pkg/system"

 	"github.com/go-check/check"

 	"github.com/moby/buildkit/frontend/dockerfile/command"

 	"github.com/opencontainers/go-digest"

@@ -3601,6 +3602,11 @@ func (s *DockerSuite) TestBuildSymlinkBreakout(c *check.C) {

 	name := "testbuildsymlinkbreakout"

 	tmpdir, err := ioutil.TempDir("", name)

 	c.Assert(err, check.IsNil)

+

+	// See https://github.com/moby/moby/pull/37770 for reason for next line.

+	tmpdir, err = system.GetLongPathName(tmpdir)

+	c.Assert(err, check.IsNil)

+

 	defer os.RemoveAll(tmpdir)

 	ctx := filepath.Join(tmpdir, "context")

 	if err := os.MkdirAll(ctx, 0755); err != nil {

new file mode 100644

@@ -0,0 +1,10 @@

+// +build !windows

+

+package system // import "github.com/docker/docker/pkg/system"

+

+// GetLongPathName converts Windows short pathnames to full pathnames.

+// For example C:\Users\ADMIN~1 --> C:\Users\Administrator.

+// It is a no-op on non-Windows platforms

+func GetLongPathName(path string) (string, error) {

+	return path, nil

+}

new file mode 100644

@@ -0,0 +1,24 @@

+package system // import "github.com/docker/docker/pkg/system"

+

+import "syscall"

+

+// GetLongPathName converts Windows short pathnames to full pathnames.

+// For example C:\Users\ADMIN~1 --> C:\Users\Administrator.

+// It is a no-op on non-Windows platforms

+func GetLongPathName(path string) (string, error) {

+	// See https://groups.google.com/forum/#!topic/golang-dev/1tufzkruoTg

+	p := syscall.StringToUTF16(path)

+	b := p // GetLongPathName says we can reuse buffer

+	n, err := syscall.GetLongPathName(&p[0], &b[0], uint32(len(b)))

+	if err != nil {

+		return "", err

+	}

+	if n > uint32(len(b)) {

+		b = make([]uint16, n)

+		_, err = syscall.GetLongPathName(&p[0], &b[0], uint32(len(b)))

+		if err != nil {

+			return "", err

+		}

+	}

+	return syscall.UTF16ToString(b), nil

+}