commands: Show server error info in browser

The main item in this commit is showing of errors with a file context when running `hugo server`.

This can be turned off: `hugo server --disableBrowserError` (can also be set in `config.toml`).

But to get there, the error handling in Hugo needed a revision. There are some items left TODO for commits soon to follow, most notable errors in content and config files.

Fixes #5284
Fixes #5290
See #5325
See #5324

73 files changed, 1886 insertions, 640 deletions

diff --git a/commands/commandeer.go b/commands/commandeer.go
index c55806980..2b76462fe 100644
--- a/commands/commandeer.go
+++ b/commands/commandeer.go
@@ -14,6 +14,15 @@
 package commands
 
 import (
+	"bytes"
+	"errors"
+
+	"github.com/gohugoio/hugo/common/herrors"
+
+	"io/ioutil"
+
+	jww "github.com/spf13/jwalterweatherman"
+
 	"os"
 	"path/filepath"
 	"regexp"
@@ -21,13 +30,13 @@ import (
 	"sync"
 	"time"
 
+	"github.com/gohugoio/hugo/common/loggers"
 	"github.com/gohugoio/hugo/config"
 
 	"github.com/spf13/cobra"
 
-	"github.com/spf13/afero"
-
 	"github.com/gohugoio/hugo/hugolib"
+	"github.com/spf13/afero"
 
 	"github.com/bep/debounce"
 	"github.com/gohugoio/hugo/common/types"
@@ -46,6 +55,8 @@ type commandeerHugoState struct {
 type commandeer struct {
 	*commandeerHugoState
 
+	logger *loggers.Logger
+
 	// Currently only set when in "fast render mode". But it seems to
 	// be fast enough that we could maybe just add it for all server modes.
 	changeDetector *fileChangeDetector
@@ -69,9 +80,45 @@ type commandeer struct {
 	serverPorts         []int
 	languagesConfigured bool
 	languages           langs.Languages
+	doLiveReload        bool
+	fastRenderMode      bool
+	showErrorInBrowser  bool
 
 	configured bool
 	paused     bool
+
+	// Any error from the last build.
+	buildErr error
+}
+
+func (c *commandeer) errCount() int {
+	return int(c.logger.ErrorCounter.Count())
+}
+
+func (c *commandeer) getErrorWithContext() interface{} {
+	errCount := c.errCount()
+
+	if errCount == 0 {
+		return nil
+	}
+
+	m := make(map[string]interface{})
+
+	m["Error"] = errors.New(removeErrorPrefixFromLog(c.logger.Errors.String()))
+	m["Version"] = hugoVersionString()
+
+	fe := herrors.UnwrapErrorWithFileContext(c.buildErr)
+	if fe != nil {
+		m["File"] = fe
+	}
+
+	if c.h.verbose {
+		var b bytes.Buffer
+		herrors.FprintStackTrace(&b, c.buildErr)
+		m["StackTrace"] = b.String()
+	}
+
+	return m
 }
 
 func (c *commandeer) Set(key string, value interface{}) {
@@ -105,6 +152,8 @@ func newCommandeer(mustHaveConfigFile, running bool, h *hugoBuilderCommon, f fla
 		doWithCommandeer:    doWithCommandeer,
 		visitedURLs:         types.NewEvictingStringQueue(10),
 		debounce:            rebuildDebouncer,
+		// This will be replaced later, but we need something to log to before the configuration is read.
+		logger: loggers.NewLogger(jww.LevelError, jww.LevelError, os.Stdout, ioutil.Discard, running),
 	}
 
 	return c, c.loadConfig(mustHaveConfigFile, running)
@@ -236,6 +285,11 @@ func (c *commandeer) loadConfig(mustHaveConfigFile, running bool) error {
 		c.languages = l
 	}
 
+	// Set some commonly used flags
+	c.doLiveReload = !c.h.buildWatch && !c.Cfg.GetBool("disableLiveReload")
+	c.fastRenderMode = c.doLiveReload && !c.Cfg.GetBool("disableFastRender")
+	c.showErrorInBrowser = c.doLiveReload && !c.Cfg.GetBool("disableBrowserError")
+
 	// This is potentially double work, but we need to do this one more time now
 	// that all the languages have been configured.
 	if c.doWithCommandeer != nil {
@@ -244,12 +298,13 @@ func (c *commandeer) loadConfig(mustHaveConfigFile, running bool) error {
 		}
 	}
 
-	logger, err := c.createLogger(config)
+	logger, err := c.createLogger(config, running)
 	if err != nil {
 		return err
 	}
 
 	cfg.Logger = logger
+	c.logger = logger
 
 	createMemFs := config.GetBool("renderToMemory")
 
diff --git a/commands/commands.go b/commands/commands.go
index 54eb03b5b..8670d4983 100644
--- a/commands/commands.go
+++ b/commands/commands.go
@@ -14,12 +14,10 @@
 package commands
 
 import (
-	"os"
-
+	"github.com/gohugoio/hugo/common/loggers"
 	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/spf13/cobra"
-	jww "github.com/spf13/jwalterweatherman"
 
 	"github.com/spf13/nitro"
 )
@@ -242,7 +240,7 @@ func (cc *hugoBuilderCommon) handleFlags(cmd *cobra.Command) {
 	_ = cmd.Flags().SetAnnotation("theme", cobra.BashCompSubdirsInDir, []string{"themes"})
 }
 
-func checkErr(logger *jww.Notepad, err error, s ...string) {
+func checkErr(logger *loggers.Logger, err error, s ...string) {
 	if err == nil {
 		return
 	}
@@ -255,25 +253,3 @@ func checkErr(logger *jww.Notepad, err error, s ...string) {
 	}
 	logger.ERROR.Println(err)
 }
-
-func stopOnErr(logger *jww.Notepad, err error, s ...string) {
-	if err == nil {
-		return
-	}
-
-	defer os.Exit(-1)
-
-	if len(s) == 0 {
-		newMessage := err.Error()
-		// Printing an empty string results in a error with
-		// no message, no bueno.
-		if newMessage != "" {
-			logger.CRITICAL.Println(newMessage)
-		}
-	}
-	for _, message := range s {
-		if message != "" {
-			logger.CRITICAL.Println(message)
-		}
-	}
-}
diff --git a/commands/convert.go b/commands/convert.go
index 8de155e9b..dc6b8fe15 100644
--- a/commands/convert.go
+++ b/commands/convert.go
@@ -14,10 +14,10 @@
 package commands
 
 import (
-	"fmt"
 	"time"
 
 	src "github.com/gohugoio/hugo/source"
+	"github.com/pkg/errors"
 
 	"github.com/gohugoio/hugo/hugolib"
 
@@ -187,7 +187,7 @@ func (cc *convertCmd) convertAndSavePage(p *hugolib.Page, site *hugolib.Site, ma
 	}
 
 	if err = newPage.SaveSourceAs(newFilename); err != nil {
-		return fmt.Errorf("Failed to save file %q: %s", newFilename, err)
+		return errors.Wrapf(err, "Failed to save file %q:", newFilename)
 	}
 
 	return nil
diff --git a/commands/hugo.go b/commands/hugo.go
index 2e7353d51..6cb2ec012 100644
--- a/commands/hugo.go
+++ b/commands/hugo.go
@@ -18,16 +18,22 @@ package commands
 import (
 	"fmt"
 	"io/ioutil"
+
 	"os/signal"
 	"sort"
 	"sync/atomic"
+
+	"github.com/pkg/errors"
+
+	"github.com/gohugoio/hugo/common/herrors"
+	"github.com/gohugoio/hugo/common/loggers"
+
 	"syscall"
 
 	"github.com/gohugoio/hugo/hugolib/filesystems"
 
 	"golang.org/x/sync/errgroup"
 
-	"log"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -85,7 +91,7 @@ func Execute(args []string) Response {
 	}
 
 	if err == nil {
-		errCount := int(jww.LogCountForLevelsGreaterThanorEqualTo(jww.LevelError))
+		errCount := int(loggers.GlobalErrorCounter.Count())
 		if errCount > 0 {
 			err = fmt.Errorf("logged %d errors", errCount)
 		} else if resp.Result != nil {
@@ -118,7 +124,7 @@ func initializeConfig(mustHaveConfigFile, running bool,
 
 }
 
-func (c *commandeer) createLogger(cfg config.Provider) (*jww.Notepad, error) {
+func (c *commandeer) createLogger(cfg config.Provider, running bool) (*loggers.Logger, error) {
 	var (
 		logHandle       = ioutil.Discard
 		logThreshold    = jww.LevelWarn
@@ -161,7 +167,7 @@ func (c *commandeer) createLogger(cfg config.Provider) (*jww.Notepad, error) {
 	jww.SetStdoutThreshold(stdoutThreshold)
 	helpers.InitLoggers()
 
-	return jww.NewNotepad(stdoutThreshold, logThreshold, outHandle, logHandle, "", log.Ldate|log.Ltime), nil
+	return loggers.NewLogger(stdoutThreshold, logThreshold, outHandle, logHandle, running), nil
 }
 
 func initializeFlags(cmd *cobra.Command, cfg config.Provider) {
@@ -275,9 +281,9 @@ func (c *commandeer) fullBuild() error {
 		cnt, err := c.copyStatic()
 		if err != nil {
 			if !os.IsNotExist(err) {
-				return fmt.Errorf("Error copying static files: %s", err)
+				return errors.Wrap(err, "Error copying static files")
 			}
-			c.Logger.WARN.Println("No Static directory found")
+			c.logger.WARN.Println("No Static directory found")
 		}
 		langCount = cnt
 		langCount = cnt
@@ -285,7 +291,7 @@ func (c *commandeer) fullBuild() error {
 	}
 	buildSitesFunc := func() error {
 		if err := c.buildSites(); err != nil {
-			return fmt.Errorf("Error building site: %s", err)
+			return errors.Wrap(err, "Error building site")
 		}
 		return nil
 	}
@@ -345,8 +351,8 @@ func (c *commandeer) build() error {
 		if err != nil {
 			return err
 		}
-		c.Logger.FEEDBACK.Println("Watching for changes in", c.hugo.PathSpec.AbsPathify(c.Cfg.GetString("contentDir")))
-		c.Logger.FEEDBACK.Println("Press Ctrl+C to stop")
+		c.logger.FEEDBACK.Println("Watching for changes in", c.hugo.PathSpec.AbsPathify(c.Cfg.GetString("contentDir")))
+		c.logger.FEEDBACK.Println("Press Ctrl+C to stop")
 		watcher, err := c.newWatcher(watchDirs...)
 		checkErr(c.Logger, err)
 		defer watcher.Close()
@@ -388,7 +394,7 @@ func (c *commandeer) doWithPublishDirs(f func(sourceFs *filesystems.SourceFilesy
 	staticFilesystems := c.hugo.BaseFs.SourceFilesystems.Static
 
 	if len(staticFilesystems) == 0 {
-		c.Logger.WARN.Println("No static directories found to sync")
+		c.logger.WARN.Println("No static directories found to sync")
 		return langCount, nil
 	}
 
@@ -448,13 +454,13 @@ func (c *commandeer) copyStaticTo(sourceFs *filesystems.SourceFilesystem) (uint6
 	syncer.Delete = c.Cfg.GetBool("cleanDestinationDir")
 
 	if syncer.Delete {
-		c.Logger.INFO.Println("removing all files from destination that don't exist in static dirs")
+		c.logger.INFO.Println("removing all files from destination that don't exist in static dirs")
 
 		syncer.DeleteFilter = func(f os.FileInfo) bool {
 			return f.IsDir() && strings.HasPrefix(f.Name(), ".")
 		}
 	}
-	c.Logger.INFO.Println("syncing static files to", publishDir)
+	c.logger.INFO.Println("syncing static files to", publishDir)
 
 	var err error
 
@@ -480,7 +486,7 @@ func (c *commandeer) timeTrack(start time.Time, name string) {
 		return
 	}
 	elapsed := time.Since(start)
-	c.Logger.FEEDBACK.Printf("%s in %v ms", name, int(1000*elapsed.Seconds()))
+	c.logger.FEEDBACK.Printf("%s in %v ms", name, int(1000*elapsed.Seconds()))
 }
 
 // getDirList provides NewWatcher() with a list of directories to watch for changes.
@@ -498,7 +504,7 @@ func (c *commandeer) getDirList() ([]string, error) {
 					return nil
 				}
 
-				c.Logger.ERROR.Println("Walker: ", err)
+				c.logger.ERROR.Println("Walker: ", err)
 				return nil
 			}
 
@@ -511,16 +517,16 @@ func (c *commandeer) getDirList() ([]string, error) {
 			if fi.Mode()&os.ModeSymlink == os.ModeSymlink {
 				link, err := filepath.EvalSymlinks(path)
 				if err != nil {
-					c.Logger.ERROR.Printf("Cannot read symbolic link '%s', error was: %s", path, err)
+					c.logger.ERROR.Printf("Cannot read symbolic link '%s', error was: %s", path, err)
 					return nil
 				}
 				linkfi, err := helpers.LstatIfPossible(c.Fs.Source, link)
 				if err != nil {
-					c.Logger.ERROR.Printf("Cannot stat %q: %s", link, err)
+					c.logger.ERROR.Printf("Cannot stat %q: %s", link, err)
 					return nil
 				}
 				if !allowSymbolicDirs && !linkfi.Mode().IsRegular() {
-					c.Logger.ERROR.Printf("Symbolic links for directories not supported, skipping %q", path)
+					c.logger.ERROR.Printf("Symbolic links for directories not supported, skipping %q", path)
 					return nil
 				}
 
@@ -603,7 +609,7 @@ func (c *commandeer) getDirList() ([]string, error) {
 
 func (c *commandeer) resetAndBuildSites() (err error) {
 	if !c.h.quiet {
-		c.Logger.FEEDBACK.Println("Started bui