Add --ignore flag

Added a --ignore flag to ignore packages and files in the build context.
This should mimic the .dockerignore file. Before starting the build, we
go through and delete ignored files from the build context.

cmd/executor/cmd/root.go

@@ -61,6 +61,9 @@ var RootCmd = &cobra.Command{
 		if err := resolveSourceContext(); err != nil {
 			return errors.Wrap(err, "error resolving source context")
 		}
+		if err := removeIgnoredFiles(); err != nil {
+			return errors.Wrap(err, "error removing ignored files from build context")
+		}
 		return resolveDockerfilePath()
 	},
 	Run: func(cmd *cobra.Command, args []string) {
@@ -91,6 +94,7 @@ func addKanikoOptionsFlags(cmd *cobra.Command) {
 	RootCmd.PersistentFlags().VarP(&opts.Destinations, "destination", "d", "Registry the final image should be pushed to. Set it repeatedly for multiple destinations.")
 	RootCmd.PersistentFlags().StringVarP(&opts.SnapshotMode, "snapshotMode", "", "full", "Change the file attributes inspected during snapshotting")
 	RootCmd.PersistentFlags().VarP(&opts.BuildArgs, "build-arg", "", "This flag allows you to pass in ARG values at build time. Set it repeatedly for multiple values.")
+	RootCmd.PersistentFlags().VarP(&opts.Ignore, "ignore", "", "Set this flag to ignore files in the build context. Set it repeatedly for multiple values.")
 	RootCmd.PersistentFlags().BoolVarP(&opts.InsecurePush, "insecure", "", false, "Push to insecure registry using plain HTTP")
 	RootCmd.PersistentFlags().BoolVarP(&opts.SkipTLSVerify, "skip-tls-verify", "", false, "Push to insecure registry ignoring TLS verify")
 	RootCmd.PersistentFlags().StringVarP(&opts.TarPath, "tarPath", "", "", "Path to save the image in as a tarball instead of pushing")
@@ -182,6 +186,35 @@ func resolveSourceContext() error {
 	return nil
 }
 
+func removeIgnoredFiles() error {
+	logrus.Infof("Removing ignored files from build context: %s", opts.Ignore)
+	for r, i := range opts.Ignore {
+		opts.Ignore[r] = filepath.Clean(filepath.Join(opts.SrcContext, i))
+	}
+	err := filepath.Walk(opts.SrcContext, func(path string, fi os.FileInfo, _ error) error {
+		if ignoreFile(path) {
+			if err := os.RemoveAll(path); err != nil {
+				logrus.Debugf("error removing %s from buildcontext", path)
+			}
+		}
+		return nil
+	})
+	return err
+}
+
+func ignoreFile(path string) bool {
+	for _, i := range opts.Ignore {
+		matched, err := filepath.Match(i, path)
+		if err != nil {
+			return false
+		}
+		if matched {
+			return true
+		}
+	}
+	return false
+}
+
 func exit(err error) {
 	fmt.Println(err)
 	os.Exit(1)