cmd/tailscale/cli/ffcomplete: omit and clean completion results

Updates #3793

Signed-off-by: Paul Scott <paul@tailscale.com>

cmd/tailscale/cli/ffcomplete/internal/complete.go

@@ -193,12 +193,26 @@ func Complete(root *ffcli.Command, args []string, startFlags, descs bool) (words
 	}
 
 	// Strip any descriptions if they were suppressed.
-	if !descs {
-		for i := range words {
-			words[i], _, _ = strings.Cut(words[i], "\t")
+	clean := words[:0]
+	for _, w := range words {
+		if !descs {
+			w, _, _ = strings.Cut(w, "\t")
 		}
+		w = cutAny(w, "\n\r")
+		if w == "" || w[0] == '\t' {
+			continue
+		}
+		clean = append(clean, w)
 	}
-	return words, dir, nil
+	return clean, dir, nil
+}
+
+func cutAny(s, cutset string) string {
+	i := strings.IndexAny(s, cutset)
+	if i == -1 {
+		return s
+	}
+	return s[:i]
 }
 
 // splitFlagArgs separates a list of command-line arguments into arguments

cmd/tailscale/cli/ffcomplete/internal/complete_test.go

@@ -50,11 +50,17 @@ func() *ffcli.Command {
 				cmd := &ffcli.Command{
 					Name: "ping",
 					FlagSet: newFlagSet("prog ping", flag.ContinueOnError, func(fs *flag.FlagSet) {
-						fs.String("until", "", "when pinging should end")
+						fs.String("until", "", "when pinging should end\nline break!")
 						ffcomplete.Flag(fs, "until", ffcomplete.Fixed("forever", "direct"))
 					}),
 				}
-				ffcomplete.Args(cmd, ffcomplete.Fixed("jupiter", "neptune", "venus"))
+				ffcomplete.Args(cmd, ffcomplete.Fixed(
+					"jupiter\t5th planet\nand largets",
+					"neptune\t8th planet",
+					"venus\t2nd planet",
+					"\tonly description",
+					"\nonly line break",
+				))
 				return cmd
 			}(),
 		},
@@ -170,9 +176,9 @@ func() *ffcli.Command {
 			showDescs: true,
 			wantComp: []string{
 				"--until\twhen pinging should end",
-				"jupiter",
-				"neptune",
-				"venus",
+				"jupiter\t5th planet",
+				"neptune\t8th planet",
+				"venus\t2nd planet",
 			},
 			wantDir: ffcomplete.ShellCompDirectiveNoFileComp,
 		},