Sort arguments in Meta.process

Meta.process was relying on the system readdir to order the arguments,
but readdir doesn't guarantee any ordering. Read the directory contents
as a whole and sort them in place before adding the tfvars files.

command/meta.go

@@ -11,6 +11,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -398,27 +399,16 @@ func (m *Meta) process(args []string, vars bool) ([]string, error) {
 		if err != nil {
 			return nil, err
 		}
-		f, err := os.Open(wd)
+
+		fis, err := ioutil.ReadDir(wd)
 		if err != nil {
 			return nil, err
 		}
-		defer f.Close()
 
-		fi, err := f.Stat()
-		if err != nil {
-			return nil, err
-		}
-		if !fi.IsDir() {
-			return nil, err
-		}
-
-		err = nil
-		for err != io.EOF {
-			var fis []os.FileInfo
-			fis, err = f.Readdir(128)
-			if err != nil && err != io.EOF {
-				return nil, err
-			}
+		// make sure we add the files in order
+		sort.Slice(fis, func(i, j int) bool {
+			return fis[i].Name() < fis[j].Name()
+		})
 
 		for _, fi := range fis {
 			name := fi.Name()
@@ -430,7 +420,6 @@ func (m *Meta) process(args []string, vars bool) ([]string, error) {
 			m.autoKey = "var-file-default"
 			preArgs = append(preArgs, "-"+m.autoKey, name)
 		}
-		}
 
 		args = append(preArgs, args...)
 	}