Add ActiveHelp to the cobra-cli (#42)

The below messages have been added.

$ cobra-cli init <TAB>
Optionally specify the path of the go module to initialize
--
CONDUCT.md       LICENSE.txt      Makefile         bin/             go.mod           main.go
CONTRIBUTING.md  MAINTAINERS      README.md        cmd/             go.sum           tpl/

$ cobra-cli init newprogram <TAB>
This command does not take any more arguments (but may accept flags)

$ cobra-cli init newprogram extra <TAB>
ERROR: Too many arguments specified

$ cobra-cli add <TAB>
Please specify the name for the new command

$ cobra-cli add command <TAB>
This command does not take any more arguments (but may accept flags)

$ cobra-cli add command command2 <TAB>
ERROR: Too many arguments specified

Signed-off-by: Marc Khouzam <marc.khouzam@gmail.com>

cmd/add.go

@@ -37,7 +37,17 @@ If you want your command to be public, pass in the command name
 with an initial uppercase letter.
 
 Example: cobra add server -> resulting in a new cmd/server.go`,
-
+		ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			var comps []string
+			if len(args) == 0 {
+				comps = cobra.AppendActiveHelp(comps, "Please specify the name for the new command")
+			} else if len(args) == 1 {
+				comps = cobra.AppendActiveHelp(comps, "This command does not take any more arguments (but may accept flags)")
+			} else {
+				comps = cobra.AppendActiveHelp(comps, "ERROR: Too many arguments specified")
+			}
+			return comps, cobra.ShellCompDirectiveNoFileComp
+		},
 		Run: func(cmd *cobra.Command, args []string) {
 			if len(args) < 1 {
 				cobra.CheckErr(fmt.Errorf("add needs a name for the command"))

cmd/init.go

@@ -36,7 +36,21 @@ and the appropriate structure for a Cobra-based CLI application.
 
 Cobra init must be run inside of a go module (please run "go mod init <MODNAME>" first)
 `,
-
+		ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			var comps []string
+			var directive cobra.ShellCompDirective
+			if len(args) == 0 {
+				comps = cobra.AppendActiveHelp(comps, "Optionally specify the path of the go module to initialize")
+				directive = cobra.ShellCompDirectiveDefault
+			} else if len(args) == 1 {
+				comps = cobra.AppendActiveHelp(comps, "This command does not take any more arguments (but may accept flags)")
+				directive = cobra.ShellCompDirectiveNoFileComp
+			} else {
+				comps = cobra.AppendActiveHelp(comps, "ERROR: Too many arguments specified")
+				directive = cobra.ShellCompDirectiveNoFileComp
+			}
+			return comps, directive
+		},
 		Run: func(_ *cobra.Command, args []string) {
 			projectPath, err := initializeProject(args)
 			cobra.CheckErr(err)