Improve error handling in commands

Cobra, the CLI commander in use in Hugo, has some long awaited improvements in the error handling department.
This enables a more centralized error handling approach.

This commit introduces that by changing all the command funcs to `RunE`:

* The core part of the error logging, usage logging and `os.Exit(-1)` is now performed in one place and that one place only.
* The usage text is now only shown on invalid arguments etc. (user errors)

Fixes gohugoio#1502

commands/benchmark.go

@@ -28,9 +28,12 @@ var benchmark = &cobra.Command{
 	Short: "Benchmark hugo by building a site a number of times.",
 	Long: `Hugo can build a site many times over and analyze the running process
 creating a benchmark.`,
-	Run: func(cmd *cobra.Command, args []string) {
-		InitializeConfig()
-		bench(cmd, args)
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if err := InitializeConfig(); err != nil {
+			return err
+		}
+
+		return bench(cmd, args)
 	},
 }
 
@@ -41,13 +44,13 @@ func init() {
 	benchmark.Flags().IntVarP(&benchmarkTimes, "count", "n", 13, "number of times to build the site")
 }
 
-func bench(cmd *cobra.Command, args []string) {
+func bench(cmd *cobra.Command, args []string) error {
 
 	if memProfilefile != "" {
 		f, err := os.Create(memProfilefile)
 
 		if err != nil {
-			panic(err)
+			return err
 		}
 		for i := 0; i < benchmarkTimes; i++ {
 			_ = buildSite()
@@ -62,7 +65,7 @@ func bench(cmd *cobra.Command, args []string) {
 		f, err := os.Create(cpuProfilefile)
 
 		if err != nil {
-			panic(err)
+			return err
 		}
 
 		pprof.StartCPUProfile(f)
@@ -72,4 +75,6 @@ func bench(cmd *cobra.Command, args []string) {
 		}
 	}
 
+	return nil
+
 }

commands/check.go

@@ -23,9 +23,13 @@ var check = &cobra.Command{
 	Short: "Check content in the source directory",
 	Long: `Hugo will perform some basic analysis on the content provided
 and will give feedback.`,
-	Run: func(cmd *cobra.Command, args []string) {
-		InitializeConfig()
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if err := InitializeConfig(); err != nil {
+			return err
+		}
 		site := hugolib.Site{}
-		site.Analyze()
+
+		return site.Analyze()
+
 	},
 }

commands/convert.go

@@ -36,19 +36,16 @@ var convertCmd = &cobra.Command{
 	Long: `Convert your content (e.g. front matter) to different formats.
 
 See convert's subcommands toJSON, toTOML and toYAML for more information.`,
-	Run: nil,
+	RunE: nil,
 }
 
 var toJSONCmd = &cobra.Command{
 	Use:   "toJSON",
 	Short: "Convert front matter to JSON",
 	Long: `toJSON converts all front matter in the content directory
 to use JSON for the front matter.`,
-	Run: func(cmd *cobra.Command, args []string) {
-		err := convertContents(rune([]byte(parser.JSON_LEAD)[0]))
-		if err != nil {
-			jww.ERROR.Println(err)
-		}
+	RunE: func(cmd *cobra.Command, args []string) error {
+		return convertContents(rune([]byte(parser.JSON_LEAD)[0]))
 	},
 }
 
@@ -57,11 +54,8 @@ var toTOMLCmd = &cobra.Command{
 	Short: "Convert front matter to TOML",
 	Long: `toTOML converts all front matter in the content directory
 to use TOML for the front matter.`,
-	Run: func(cmd *cobra.Command, args []string) {
-		err := convertContents(rune([]byte(parser.TOML_LEAD)[0]))
-		if err != nil {
-			jww.ERROR.Println(err)
-		}
+	RunE: func(cmd *cobra.Command, args []string) error {
+		return convertContents(rune([]byte(parser.TOML_LEAD)[0]))
 	},
 }
 
@@ -70,11 +64,8 @@ var toYAMLCmd = &cobra.Command{
 	Short: "Convert front matter to YAML",
 	Long: `toYAML converts all front matter in the content directory
 to use YAML for the front matter.`,
-	Run: func(cmd *cobra.Command, args []string) {
-		err := convertContents(rune([]byte(parser.YAML_LEAD)[0]))
-		if err != nil {
-			jww.ERROR.Println(err)
-		}
+	RunE: func(cmd *cobra.Command, args []string) error {
+		return convertContents(rune([]byte(parser.YAML_LEAD)[0]))
 	},
 }
 
@@ -87,7 +78,9 @@ func init() {
 }
 
 func convertContents(mark rune) (err error) {
-	InitializeConfig()
+	if err := InitializeConfig(); err != nil {
+		return err
+	}
 	site := &hugolib.Site{}
 
 	if err := site.Initialise(); err != nil {

commands/genautocomplete.go

@@ -31,16 +31,19 @@ or just source them in directly:
 
 	$ . /etc/bash_completion`,
 
-	Run: func(cmd *cobra.Command, args []string) {
+	RunE: func(cmd *cobra.Command, args []string) error {
 		if autocompleteType != "bash" {
-			jww.FATAL.Fatalln("Only Bash is supported for now")
+			return newUserError("Only Bash is supported for now")
 		}
+
 		err := cmd.Root().GenBashCompletionFile(autocompleteTarget)
+
 		if err != nil {
-			jww.FATAL.Fatalln("Failed to generate shell completion file:", err)
+			return err
 		} else {
 			jww.FEEDBACK.Println("Bash completion file for Hugo saved to", autocompleteTarget)
 		}
+		return nil
 	},
 }
 

commands/gendoc.go

@@ -32,7 +32,7 @@ of Hugo's command-line interface for http://gohugo.io/.
 It creates one Markdown file per command with front matter suitable
 for rendering in Hugo.`,
 
-	Run: func(cmd *cobra.Command, args []string) {
+	RunE: func(cmd *cobra.Command, args []string) error {
 		if !strings.HasSuffix(gendocdir, helpers.FilePathSeparator) {
 			gendocdir += helpers.FilePathSeparator
 		}
@@ -55,6 +55,8 @@ for rendering in Hugo.`,
 		jww.FEEDBACK.Println("Generating Hugo command-line documentation in", gendocdir, "...")
 		cobra.GenMarkdownTreeCustom(cmd.Root(), gendocdir, prepender, linkHandler)
 		jww.FEEDBACK.Println("Done.")
+
+		return nil
 	},
 }
 

commands/genman.go

@@ -18,7 +18,7 @@ var genmanCmd = &cobra.Command{
 command-line interface.  By default, it creates the man page files
 in the "man" directory under the current directory.`,
 
-	Run: func(cmd *cobra.Command, args []string) {
+	RunE: func(cmd *cobra.Command, args []string) error {
 		header := &cobra.GenManHeader{
 			Section: "1",
 			Manual:  "Hugo Manual",
@@ -37,6 +37,8 @@ in the "man" directory under the current directory.`,
 		cmd.Root().GenManTree(header, genmandir)
 
 		jww.FEEDBACK.Println("Done.")
+
+		return nil
 	},
 }
 

commands/hugo.go

@@ -40,8 +40,44 @@ import (
 	"github.com/spf13/nitro"
 	"github.com/spf13/viper"
 	"gopkg.in/fsnotify.v1"
+	"regexp"
 )
 
+// userError is an error used to signal different error situations in command handling.
+type commandError struct {
+	s         string
+	userError bool
+}
+
+func (u commandError) Error() string {
+	return u.s
+}
+
+func (u commandError) isUserError() bool {
+	return u.userError
+}
+
+func newUserError(messages ...interface{}) commandError {
+	return commandError{s: fmt.Sprintln(messages...), userError: true}
+}
+
+func newSystemError(messages ...interface{}) commandError {
+	return commandError{s: fmt.Sprintln(messages...), userError: false}
+}
+
+// catch some of the obvious user errors from Cobra.
+// We don't want to show the usage message for every error.
+// The below may be to generic. Time will show.
+var userErrorRegexp = regexp.MustCompile("argument|flag|shorthand")
+
+func isUserError(err error) bool {
+	if cErr, ok := err.(commandError); ok && cErr.isUserError() {
+		return true
+	}
+
+	return userErrorRegexp.MatchString(err.Error())
+}
+
 //HugoCmd is Hugo's root command. Every other command attached to HugoCmd is a child command to it.
 var HugoCmd = &cobra.Command{
 	Use:   "hugo",
@@ -52,10 +88,15 @@ Hugo is a Fast and Flexible Static Site Generator
 built with love by spf13 and friends in Go.
 
 Complete documentation is available at http://gohugo.io/.`,
-	Run: func(cmd *cobra.Command, args []string) {
-		InitializeConfig()
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if err := InitializeConfig(); err != nil {
+			return err
+		}
+
 		watchConfig()
-		build()
+
+		return build()
+
 	},
 }
 
@@ -68,9 +109,17 @@ var Source, CacheDir, Destination, Theme, BaseURL, CfgFile, LogFile, Editor stri
 //Execute adds all child commands to the root command HugoCmd and sets flags appropriately.
 func Execute() {
 	HugoCmd.SetGlobalNormalizationFunc(helpers.NormalizeHugoFlags)
+
+	HugoCmd.SilenceUsage = true
+
 	AddCommands()
-	if err := HugoCmd.Execute(); err != nil {
-		// the err is already logged by Cobra
+
+	if c, err := HugoCmd.ExecuteC(); err != nil {
+		if isUserError(err) {
+			c.Println("")
+			c.Println(c.UsageString())
+		}
+
 		os.Exit(-1)
 	}
 }
@@ -184,7 +233,7 @@ func LoadDefaultSettings() {
 }
 
 // InitializeConfig initializes a config file with sensible default configuration flags.
-func InitializeConfig() {
+func InitializeConfig() error {
 	viper.SetConfigFile(CfgFile)
 	// See https://github.com/spf13/viper/issues/73#issuecomment-126970794
 	if Source == "" {
@@ -195,9 +244,9 @@ func InitializeConfig() {
 	err := viper.ReadInConfig()
 	if err != nil {
 		if _, ok := err.(viper.ConfigParseError); ok {
-			jww.ERROR.Println(err)
+			return newSystemError(err)
 		} else {
-			jww.ERROR.Println("Unable to locate Config file. Perhaps you need to create a new site. Run `hugo help new` for details", err)
+			return newSystemError("Unable to locate Config file. Perhaps you need to create a new site. Run `hugo help new` for details", err)
 		}
 	}
 
@@ -320,7 +369,7 @@ func InitializeConfig() {
 	themeDir := helpers.GetThemeDir()
 	if themeDir != "" {
 		if _, err := os.Stat(themeDir); os.IsNotExist(err) {
-			jww.FATAL.Fatalln("Unable to find theme Directory:", themeDir)
+			return newSystemError("Unable to find theme Directory:", themeDir)
 		}
 	}
 
@@ -330,6 +379,8 @@ func InitializeConfig() {
 		jww.ERROR.Printf("Current theme does not support Hugo version %s. Minimum version required is %s\n",
 			helpers.HugoReleaseVersion(), minVersion)
 	}
+
+	return nil
 }
 
 func watchConfig() {
@@ -344,23 +395,26 @@ func watchConfig() {
 	})
 }
 
-func build(watches ...bool) {
-	err := copyStatic()
-	if err != nil {
-		fmt.Println(err)
-		utils.StopOnErr(err, fmt.Sprintf("Error copying static files to %s", helpers.AbsPathify(viper.GetString("PublishDir"))))
+func build(watches ...bool) error {
+
+	if err := copyStatic(); err != nil {
+		return fmt.Errorf("Error copying static files to %s: %s", helpers.AbsPathify(viper.GetString("PublishDir")), err)
 	}
 	watch := false
 	if len(watches) > 0 && watches[0] {
 		watch = true
 	}
-	utils.StopOnErr(buildSite(BuildWatch || watch))
+	if err := buildSite(BuildWatch || watch); err != nil {
+		return fmt.Errorf("Error building site: %s", err)
+	}
 
 	if BuildWatch {
 		jww.FEEDBACK.Println("Watching for changes in", helpers.AbsPathify(viper.GetString("ContentDir")))
 		jww.FEEDBACK.Println("Press Ctrl+C to stop")
 		utils.CheckErr(NewWatcher(0))
 	}
+
+	return nil
 }
 
 func copyStatic() error {
@@ -483,7 +537,6 @@ func NewWatcher(port int) error {
 	var wg sync.WaitGroup
 
 	if err != nil {
-		fmt.Println(err)
 		return err
 	}