builder: fix build cache hash for broken symlink

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
Upstream-commit: 793ebdbf4b187b3680aed0073643040ddbeef523
Component: engine

components/engine/builder/remotecontext/archive.go

@@ -122,8 +122,5 @@ func normalize(path string, root containerfs.ContainerFS) (cleanPath, fullPath s
 	if err != nil {
 		return "", "", errors.Wrapf(err, "forbidden path outside the build context: %s (%s)", path, cleanPath)
 	}
-	if _, err := root.Lstat(fullPath); err != nil {
-		return "", "", errors.WithStack(convertPathError(err, path))
-	}
 	return
 }

components/engine/builder/remotecontext/lazycontext.go

@@ -40,16 +40,16 @@ func (c *lazySource) Hash(path string) (string, error) {
 		return "", err
 	}
 
-	fi, err := c.root.Lstat(fullPath)
-	if err != nil {
-		return "", errors.WithStack(err)
-	}
-
 	relPath, err := Rel(c.root, fullPath)
 	if err != nil {
 		return "", errors.WithStack(convertPathError(err, cleanPath))
 	}
 
+	fi, err := os.Lstat(fullPath)
+	if err != nil {
+		return relPath, nil
+	}
+
 	sum, ok := c.sums[relPath]
 	if !ok {
 		sum, err = c.prepareHash(relPath, fi)