use cobra command Annotations to identify mutating commands

some downstream applications need to know which sub-commands
may alter the index.  this new function allows them to be
identified, while not prescribing any particular behavior.

cmd/bleve/cmd/bulk.go

@@ -31,6 +31,9 @@ var bulkCmd = &cobra.Command{
 	Use:   "bulk [index path] [data paths ...]",
 	Short: "bulk loads from newline delimited JSON files",
 	Long:  `The bulk command will perform batch loading of documents in one or more newline delimited JSON files.`,
+	Annotations: map[string]string{
+		canMutateBleveIndex: "true",
+	},
 	RunE: func(cmd *cobra.Command, args []string) error {
 		if len(args) < 2 {
 			return fmt.Errorf("must specify at least one path")

cmd/bleve/cmd/create.go

@@ -31,6 +31,9 @@ var createCmd = &cobra.Command{
 	Use:   "create [index path]",
 	Short: "creates a new index",
 	Long:  `The create command will create a new empty index.`,
+	Annotations: map[string]string{
+		canMutateBleveIndex: "true",
+	},
 	PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
 		// override RootCmd version which opens existing index
 		if len(args) < 1 {

cmd/bleve/cmd/index.go

@@ -32,6 +32,9 @@ var indexCmd = &cobra.Command{
 	Use:   "index [index path] [data paths ...]",
 	Short: "adds the files to the index",
 	Long:  `The index command adds the specified files to the index.`,
+	Annotations: map[string]string{
+		canMutateBleveIndex: "true",
+	},
 	RunE: func(cmd *cobra.Command, args []string) error {
 		if len(args) < 2 {
 			return fmt.Errorf("must specify at least one path")

cmd/bleve/cmd/root.go

@@ -17,6 +17,7 @@ package cmd
 import (
 	"fmt"
 	"os"
+	"strconv"
 
 	"github.com/blevesearch/bleve"
 	"github.com/spf13/cobra"
@@ -26,6 +27,22 @@ var cfgFile string
 
 var idx bleve.Index
 
+const canMutateBleveIndex = "canMutateBleveIndex"
+
+// CanMutateBleveIndex returns true if the command is capable
+// of mutating the bleve index, or false if its operation is
+// read-only
+func CanMutateBleveIndex(c *cobra.Command) bool {
+	for k, v := range c.Annotations {
+		if k == canMutateBleveIndex {
+			if b, err := strconv.ParseBool(v); err == nil && b {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 // RootCmd represents the base command when called without any subcommands
 var RootCmd = &cobra.Command{
 	Use:   "bleve",