Support a simplified kong.Groups{<key>: <title>} way of specifiying groups.

See #135.

build.go

@@ -232,7 +232,7 @@ func buildGroupForKey(k *Kong, key string) *Group {
 		}
 	}
 
-	// No group provided with kong.Groups. We create one ad-hoc for this key.
+	// No group provided with kong.ExplicitGroups. We create one ad-hoc for this key.
 	return &Group{
 		Key:   key,
 		Title: key,

help.go

@@ -150,8 +150,8 @@ func printNodeDetail(w *helpWriter, node *Node, hide bool) {
 			if group.Metadata.Title != "" {
 				w.Print(group.Metadata.Title)
 			}
-			if group.Metadata.Header != "" {
-				w.Print(group.Metadata.Header)
+			if group.Metadata.Description != "" {
+				w.Print(group.Metadata.Description)
 			}
 			writeFlags(w.Indent(), group.Flags)
 		}
@@ -170,8 +170,8 @@ func printNodeDetail(w *helpWriter, node *Node, hide bool) {
 				if group.Metadata.Title != "" {
 					w.Print(group.Metadata.Title)
 				}
-				if group.Metadata.Header != "" {
-					w.Print(group.Metadata.Header)
+				if group.Metadata.Description != "" {
+					w.Print(group.Metadata.Description)
 				}
 
 				if w.Compact {

help_test.go

@@ -295,20 +295,11 @@ func TestHelpGrouping(t *testing.T) {
 	app := mustNew(t, &cli,
 		kong.Name("test-app"),
 		kong.Description("A test app."),
-		kong.Groups([]kong.Group{
-			{
-				Key:    "Group A",
-				Title:  "Group title taken from the kong.Groups option",
-				Header: "A group header",
-			},
-			{
-				Key:   "Group 1",
-				Title: "Another group title, this time without header",
-			},
-			{
-				Key: "Unknown key",
-			},
-		}),
+		kong.Groups{
+			"Group A":     "Group title taken from the kong.ExplicitGroups option\nA group header",
+			"Group 1":     "Another group title, this time without header",
+			"Unknown key": "",
+		},
 		kong.Writers(w, w),
 		kong.Exit(func(int) {
 			exited = true
@@ -331,7 +322,7 @@ Flags:
       --free-string=STRING    A non grouped string flag.
       --free-bool             A non grouped bool flag.
 
-Group title taken from the kong.Groups option
+Group title taken from the kong.ExplicitGroups option
 A group header
   --grouped-a-string=STRING    A string flag grouped in A.
   --grouped-a-bool             A bool flag grouped in A.
@@ -343,7 +334,7 @@ Commands:
   two
     A non grouped subcommand.
 
-Group title taken from the kong.Groups option
+Group title taken from the kong.ExplicitGroups option
 A group header
   one thing <arg>
     subcommand thing
@@ -387,7 +378,7 @@ Flags:
 
       --a-free-string=STRING    A non grouped string flag.
 
-Group title taken from the kong.Groups option
+Group title taken from the kong.ExplicitGroups option
 A group header
   --grouped-a-string=STRING    A string flag grouped in A.
   --grouped-a-bool             A bool flag grouped in A.

model.go

@@ -412,9 +412,9 @@ type Group struct {
 	Key string
 	// Title is displayed above the grouped items.
 	Title string
-	// Header is optional and displayed under the Title when non empty.
+	// Description is optional and displayed under the Title when non empty.
 	// It can be used to introduce the group's purpose to the user.
-	Header string
+	Description string
 }
 
 // This is directly from the Go 1.13 source code.

options.go

@@ -208,10 +208,40 @@ func ConfigureHelp(options HelpOptions) Option {
 	})
 }
 
-// Groups associates `group` field tags with their metadata.
+// Groups associates `group` field tags with group metadata.
+//
+// This option is used to simplify Kong tags while providing
+// rich group information such as title and optional description.
+//
+// Each key in the "groups" map corresponds to the value of a
+// `group` Kong tag, while the first line of the value will be
+// the title, and subsequent lines if any will be the description of
+// the group.
+//
+// See also ExplicitGroups for a more structured alternative.
+type Groups map[string]string
+
+func (g Groups) Apply(k *Kong) error { // nolint: golint
+	for key, info := range g {
+		lines := strings.Split(info, "\n")
+		title := strings.TrimSpace(lines[0])
+		description := ""
+		if len(lines) > 1 {
+			description = strings.TrimSpace(strings.Join(lines[1:], "\n"))
+		}
+		k.groups = append(k.groups, Group{
+			Key:         key,
+			Title:       title,
+			Description: description,
+		})
+	}
+	return nil
+}
+
+// ExplicitGroups associates `group` field tags with their metadata.
 //
 // It can be used to provide a title or header to a command or flag group.
-func Groups(groups []Group) Option {
+func ExplicitGroups(groups []Group) Option {
 	return OptionFunc(func(k *Kong) error {
 		k.groups = groups
 		return nil