hierarchy: provide option to list the used keywords in a spec

To increase a user's control on how they validate a directory or
tar archive with a specification, it is helpful to know which
keywords are actually used in the spec provided. This way, the user
can see what keywords to use or not use with the '-k' or '-K' flags.

Signed-off-by: Stephen Chung <schung@redhat.com>

cmd/gomtree/main.go

@@ -24,7 +24,7 @@ var (
 	flResultFormat     = flag.String("result-format", "bsd", "output the validation results using the given format (bsd, json, path)")
 	flTar              = flag.String("T", "", "use tar archive to create or validate a directory hierarchy spec")
 	flBsdKeywords      = flag.Bool("bsd-keywords", false, "only operate on keywords that are supported by upstream mtree(8)")
-
+	flListUsedKeywords = flag.Bool("list-used", false, "list all the keywords found in a validation manifest")
 	flDebug            = flag.Bool("debug", false, "output debug info to STDERR")
 )
 
@@ -156,6 +156,25 @@ func main() {
 		}
 	}
 
+	// -list-used
+	if *flListUsedKeywords {
+		if *flFile == "" {
+			log.Println("no specification provided. please provide a validation manifest")
+			defer os.Exit(1)
+			isErr = true
+			return
+		}
+		fmt.Printf("Keywords used in [%s]:\n", *flFile)
+		for _, kw := range mtree.CollectUsedKeywords(dh) {
+			fmt.Printf(" %s", kw)
+			if _, ok := mtree.KeywordFuncs[kw]; !ok {
+				fmt.Print(" (unsupported)")
+			}
+			fmt.Printf("\n")
+		}
+		return
+	}
+
 	// -p <path>
 	var rootPath = "."
 	if *flPath != "" {

hierarchy.go

@@ -25,3 +25,27 @@ func (dh DirectoryHierarchy) WriteTo(w io.Writer) (n int64, err error) {
 	}
 	return sum, nil
 }
+
+// CollectUsedKeywords collects and returns all the keywords used in a
+// a DirectoryHierarchy
+func CollectUsedKeywords(dh *DirectoryHierarchy) []string {
+	if dh != nil {
+		usedkeywords := []string{}
+		for _, e := range dh.Entries {
+			switch e.Type {
+			case FullType, RelativeType, SpecialType:
+				if e.Type != SpecialType || e.Name == "/set" {
+					kvs := e.Keywords
+					for _, kv := range kvs {
+						kw := KeyVal(kv).Keyword()
+						if !inSlice(kw, usedkeywords) {
+							usedkeywords = append(usedkeywords, kw)
+						}
+					}
+				}
+			}
+		}
+		return usedkeywords
+	}
+	return nil
+}