Add gendoc command

Using the new, great auto-doc in Cobra.

This commit also contains a current result of that command added to a commands section in docs.

Fixes #1136

commands/gendoc.go

@@ -0,0 +1,59 @@
+package commands
+
+import (
+	"fmt"
+	"github.com/spf13/cobra"
+	"github.com/spf13/hugo/helpers"
+	"github.com/spf13/hugo/hugofs"
+	"path"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+const gendocFrontmatterTemplate = `---
+date: %s
+title: "%s"
+slug: %s
+url: %s
+---
+`
+
+var gendocdir string
+var gendocCmd = &cobra.Command{
+	Use:   "gendoc",
+	Short: "Generate Markdown documentation for the Hugo CLI.",
+	Long: `Generate Markdown documentation for the Hugo CLI.
+	
+	This command is, mostly, used to create up-to-date documentation for gohugo.io.
+	
+	It creates one Markdown file per command with front matter suitable for rendering in Hugo.
+	`,
+
+	Run: func(cmd *cobra.Command, args []string) {
+		if !strings.HasSuffix(gendocdir, helpers.FilePathSeparator) {
+			gendocdir += helpers.FilePathSeparator
+		}
+		if found, _ := helpers.Exists(gendocdir, hugofs.OsFs); !found {
+			hugofs.OsFs.Mkdir(gendocdir, 0777)
+		}
+		now := time.Now().Format(time.RFC3339)
+		prepender := func(filename string) string {
+			name := filepath.Base(filename)
+			base := strings.TrimSuffix(name, path.Ext(name))
+			url := "/commands/" + strings.ToLower(base) + "/"
+			return fmt.Sprintf(gendocFrontmatterTemplate, now, strings.Replace(base, "_", " ", -1), base, url)
+		}
+
+		linkHandler := func(name string) string {
+			base := strings.TrimSuffix(name, path.Ext(name))
+			return "/commands/" + strings.ToLower(base) + "/"
+		}
+
+		cobra.GenMarkdownTreeCustom(cmd.Root(), gendocdir, prepender, linkHandler)
+	},
+}
+
+func init() {
+	gendocCmd.PersistentFlags().StringVar(&gendocdir, "dir", "/tmp/hugodoc/", "the directory to write the doc.")
+}