i18n/xgettext-go: implement the -D/--directory option of GNU xgettext

i18n/xgettext-go/main.go

@@ -10,6 +10,7 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
+	"path/filepath"
 	"sort"
 	"strings"
 	"time"
@@ -170,8 +171,26 @@ func processFiles(args []string) error {
 	return nil
 }
 
+func readContent(fname string) (content []byte, err error) {
+	// If no search directories have been specified or we have an
+	// absolute path, just try to read the contents directly.
+	if len(opts.Directories) == 0 || filepath.IsAbs(fname) {
+		return ioutil.ReadFile(fname)
+	}
+
+	// Otherwise, search for the file in each of the configured
+	// directories.
+	for _, dir := range opts.Directories {
+		content, err = ioutil.ReadFile(filepath.Join(dir, fname))
+		if !os.IsNotExist(err) {
+			break
+		}
+	}
+	return content, err
+}
+
 func processSingleGoSource(fset *token.FileSet, fname string) error {
-	fnameContent, err := ioutil.ReadFile(fname)
+	fnameContent, err := readContent(fname)
 	if err != nil {
 		return err
 	}
@@ -277,6 +296,8 @@ msgstr  "Project-Id-Version: %s\n"
 var opts struct {
 	FilesFrom string `short:"f" long:"files-from" description:"get list of input files from FILE"`
 
+	Directories []string `short:"D" long:"directory" description:"add DIRECTORY to list for input files search"`
+
 	Output string `short:"o" long:"output" description:"output to specified file"`
 
 	AddComments bool `short:"c" long:"add-comments" description:"place all comment blocks preceding keyword lines in output file"`