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

create/content.go

@@ -16,7 +16,9 @@ package create
 
 import (
 	"bytes"
-	"fmt"
+
+	"github.com/pkg/errors"
+
 	"io"
 	"os"
 	"os/exec"
@@ -135,7 +137,7 @@ func newContentFromDir(
 
 		targetDir := filepath.Dir(targetFilename)
 		if err := targetFs.MkdirAll(targetDir, 0777); err != nil && !os.IsExist(err) {
-			return fmt.Errorf("failed to create target directory for %s: %s", targetDir, err)
+			return errors.Wrapf(err, "failed to create target directory for %s:", targetDir)
 		}
 
 		out, err := targetFs.Create(targetFilename)
@@ -223,7 +225,7 @@ func mapArcheTypeDir(
 func usesSiteVar(fs afero.Fs, filename string) (bool, error) {
 	f, err := fs.Open(filename)
 	if err != nil {
-		return false, fmt.Errorf("failed to open archetype file: %s", err)
+		return false, errors.Wrap(err, "failed to open archetype file")
 	}
 	defer f.Close()
 	return helpers.ReaderContains(f, []byte(".Site")), nil

create/content_template_handler.go

@@ -20,6 +20,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/pkg/errors"
+
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/gohugoio/hugo/source"
 
@@ -127,14 +129,14 @@ func executeArcheTypeAsTemplate(s *hugolib.Site, name, kind, targetPath, archety
 	templateHandler := s.Deps.Tmpl.(tpl.TemplateHandler)
 	templateName := "_text/" + helpers.Filename(archetypeFilename)
 	if err := templateHandler.AddTemplate(templateName, string(archetypeTemplate)); err != nil {
-		return nil, fmt.Errorf("Failed to parse archetype file %q: %s", archetypeFilename, err)
+		return nil, errors.Wrapf(err, "Failed to parse archetype file %q:", archetypeFilename)
 	}
 
 	templ, _ := templateHandler.Lookup(templateName)
 
 	var buff bytes.Buffer
 	if err := templ.Execute(&buff, data); err != nil {
-		return nil, fmt.Errorf("Failed to process archetype file %q: %s", archetypeFilename, err)
+		return nil, errors.Wrapf(err, "Failed to process archetype file %q:", archetypeFilename)
 	}
 
 	archetypeContent = []byte(archetypeShortcodeReplacementsPost.Replace(buff.String()))