hugolib: Add option to disable rendering of 404 page

Fixes #1889
Closes #2037

commands/hugo.go

@@ -127,6 +127,7 @@ var (
 	canonifyURLs          bool
 	cleanDestination      bool
 	enableRobotsTXT       bool
+	disable404            bool
 	disableRSS            bool
 	disableSitemap        bool
 	draft                 bool
@@ -214,6 +215,7 @@ func initHugoBuildCommonFlags(cmd *cobra.Command) {
 	cmd.Flags().BoolVar(&cleanDestination, "cleanDestinationDir", false, "Remove files from destination not found in static directories")
 	cmd.Flags().BoolVarP(&draft, "buildDrafts", "D", false, "include content marked as draft")
 	cmd.Flags().BoolVarP(&future, "buildFuture", "F", false, "include content with publishdate in the future")
+	cmd.Flags().BoolVar(&disable404, "disable404", false, "Do not render 404 page")
 	cmd.Flags().BoolVar(&disableRSS, "disableRSS", false, "Do not build RSS files")
 	cmd.Flags().BoolVar(&disableSitemap, "disableSitemap", false, "Do not build Sitemap file")
 	cmd.Flags().StringVarP(&source, "source", "s", "", "filesystem path to read files relative from")
@@ -266,6 +268,7 @@ func loadDefaultSettings() {
 	viper.SetDefault("cleanDestinationDir", false)
 	viper.SetDefault("Watch", false)
 	viper.SetDefault("MetaDataFormat", "toml")
+	viper.SetDefault("Disable404", false)
 	viper.SetDefault("DisableRSS", false)
 	viper.SetDefault("DisableSitemap", false)
 	viper.SetDefault("DisableRobotsTXT", false)
@@ -357,6 +360,9 @@ func InitializeConfig(subCmdVs ...*cobra.Command) error {
 		if flagChanged(cmdV.Flags(), "canonifyURLs") {
 			viper.Set("CanonifyURLs", canonifyURLs)
 		}
+		if flagChanged(cmdV.Flags(), "disable404") {
+			viper.Set("Disable404", disable404)
+		}
 		if flagChanged(cmdV.Flags(), "disableRSS") {
 			viper.Set("DisableRSS", disableRSS)
 		}