Improve error messages, esp. when the server is running

* Add file context to minifier errors when publishing
* Misc fixes (see issues)
* Allow custom server error template in layouts/server/error.html

To get to this, this commit also cleans up and simplifies the code surrounding errors and files. This also removes the usage of `github.com/pkg/errors`, mostly because of https://github.com/pkg/errors/issues/223 -- but also because most of this is now built-in to Go.

Fixes #9852
Fixes #9857
Fixes #9863

4 files changed, 33 insertions, 36 deletions

diff --git a/modules/client.go b/modules/client.go
index 6e1cfe881..78ba9f5ae 100644
--- a/modules/client.go
+++ b/modules/client.go
@@ -47,7 +47,8 @@ import (
 
 	"github.com/gohugoio/hugo/common/hugio"
 
-	"github.com/pkg/errors"
+	"errors"
+
 	"github.com/spf13/afero"
 )
 
@@ -241,7 +242,7 @@ func (c *Client) Vendor() error {
 		// See https://github.com/gohugoio/hugo/issues/8239
 		// This is an error situation. We need something to vendor.
 		if t.Mounts() == nil {
-			return errors.Errorf("cannot vendor module %q, need at least one mount", t.Path())
+			return fmt.Errorf("cannot vendor module %q, need at least one mount", t.Path())
 		}
 
 		fmt.Fprintln(&modulesContent, "# "+t.Path()+" "+t.Version())
@@ -253,22 +254,22 @@ func (c *Client) Vendor() error {
 			targetFilename := filepath.Join(vendorDir, t.Path(), mount.Source)
 			fi, err := c.fs.Stat(sourceFilename)
 			if err != nil {
-				return errors.Wrap(err, "failed to vendor module")
+				return fmt.Errorf("failed to vendor module: %w", err)
 			}
 
 			if fi.IsDir() {
 				if err := hugio.CopyDir(c.fs, sourceFilename, targetFilename, nil); err != nil {
-					return errors.Wrap(err, "failed to copy module to vendor dir")
+					return fmt.Errorf("failed to copy module to vendor dir: %w", err)
 				}
 			} else {
 				targetDir := filepath.Dir(targetFilename)
 
 				if err := c.fs.MkdirAll(targetDir, 0755); err != nil {
-					return errors.Wrap(err, "failed to make target dir")
+					return fmt.Errorf("failed to make target dir: %w", err)
 				}
 
 				if err := hugio.CopyFile(c.fs, sourceFilename, targetFilename); err != nil {
-					return errors.Wrap(err, "failed to copy module file to vendor")
+					return fmt.Errorf("failed to copy module file to vendor: %w", err)
 				}
 			}
 		}
@@ -278,7 +279,7 @@ func (c *Client) Vendor() error {
 		_, err := c.fs.Stat(resourcesDir)
 		if err == nil {
 			if err := hugio.CopyDir(c.fs, resourcesDir, filepath.Join(vendorDir, t.Path(), files.FolderResources), nil); err != nil {
-				return errors.Wrap(err, "failed to copy resources to vendor dir")
+				return fmt.Errorf("failed to copy resources to vendor dir: %w", err)
 			}
 		}
 
@@ -287,7 +288,7 @@ func (c *Client) Vendor() error {
 		_, err = c.fs.Stat(configDir)
 		if err == nil {
 			if err := hugio.CopyDir(c.fs, configDir, filepath.Join(vendorDir, t.Path(), "config"), nil); err != nil {
-				return errors.Wrap(err, "failed to copy config dir to vendor dir")
+				return fmt.Errorf("failed to copy config dir to vendor dir: %w", err)
 			}
 		}
 
@@ -361,7 +362,7 @@ func (c *Client) get(args ...string) error {
 		args = append([]string{"-d"}, args...)
 	}
 	if err := c.runGo(context.Background(), c.logger.Out(), append([]string{"get"}, args...)...); err != nil {
-		errors.Wrapf(err, "failed to get %q", args)
+		return fmt.Errorf("failed to get %q: %w", args, err)
 	}
 	return nil
 }
@@ -372,7 +373,7 @@ func (c *Client) get(args ...string) error {
 func (c *Client) Init(path string) error {
 	err := c.runGo(context.Background(), c.logger.Out(), "mod", "init", path)
 	if err != nil {
-		return errors.Wrap(err, "failed to init modules")
+		return fmt.Errorf("failed to init modules: %w", err)
 	}
 
 	c.GoModulesFilename = filepath.Join(c.ccfg.WorkingDir, goModFilename)
@@ -458,7 +459,7 @@ func (c *Client) listGoMods() (goModules, error) {
 		out := ioutil.Discard
 		err := c.runGo(context.Background(), out, args...)
 		if err != nil {
-			return errors.Wrap(err, "failed to download modules")
+			return fmt.Errorf("failed to download modules: %w", err)
 		}
 		return nil
 	}
@@ -477,7 +478,7 @@ func (c *Client) listGoMods() (goModules, error) {
 		}
 		err := c.runGo(context.Background(), b, args...)
 		if err != nil {
-			return errors.Wrap(err, "failed to list modules")
+			return fmt.Errorf("failed to list modules: %w", err)
 		}
 
 		dec := json.NewDecoder(b)
@@ -487,7 +488,7 @@ func (c *Client) listGoMods() (goModules, error) {
 				if err == io.EOF {
 					break
 				}
-				return errors.Wrap(err, "failed to decode modules list")
+				return fmt.Errorf("failed to decode modules list: %w", err)
 			}
 
 			if err := handle(m); err != nil {
@@ -657,7 +658,7 @@ If you then run 'hugo mod graph' it should resolve itself to the most recent ver
 
 		_, ok := err.(*exec.ExitError)
 		if !ok {
-			return errors.Errorf("failed to execute 'go %v': %s %T", args, err, err)
+			return fmt.Errorf("failed to execute 'go %v': %s %T", args, err, err)
 		}
 
 		// Too old Go version
@@ -666,7 +667,7 @@ If you then run 'hugo mod graph' it should resolve itself to the most recent ver
 			return nil
 		}
 
-		return errors.Errorf("go command failed: %s", stderr)
+		return fmt.Errorf("go command failed: %s", stderr)
 
 	}
 
@@ -706,7 +707,7 @@ func (c *Client) shouldVendor(path string) bool {
 }
 
 func (c *Client) createThemeDirname(modulePath string, isProjectMod bool) (string, error) {
-	invalid := errors.Errorf("invalid module path %q; must be relative to themesDir when defined outside of the project", modulePath)
+	invalid := fmt.Errorf("invalid module path %q; must be relative to themesDir when defined outside of the project", modulePath)
 
 	modulePath = filepath.Clean(modulePath)
 	if filepath.IsAbs(modulePath) {
diff --git a/modules/collect.go b/modules/collect.go
index e012d4696..ff83f9ecc 100644
--- a/modules/collect.go
+++ b/modules/collect.go
@@ -36,7 +36,7 @@ import (
 
 	"github.com/rogpeppe/go-internal/module"
 
-	"github.com/pkg/errors"
+	"errors"
 
 	"github.com/gohugoio/hugo/config"
 	"github.com/spf13/afero"
@@ -48,7 +48,7 @@ const vendorModulesFilename = "modules.txt"
 
 // IsNotExist returns whether an error means that a module could not be found.
 func IsNotExist(err error) bool {
-	return errors.Cause(err) == ErrNotExist
+	return errors.Is(err, os.ErrNotExist)
 }
 
 // CreateProjectModule creates modules from the given config.
@@ -289,7 +289,7 @@ func (c *collector) add(owner *moduleAdapter, moduleImport Import, disabled bool
 					return nil, nil
 				}
 				if found, _ := afero.Exists(c.fs, moduleDir); !found {
-					c.err = c.wrapModuleNotFound(errors.Errorf(`module %q not found; either add it as a Hugo Module or store it in %q.`, modulePath, c.ccfg.ThemesDir))
+					c.err = c.wrapModuleNotFound(fmt.Errorf(`module %q not found; either add it as a Hugo Module or store it in %q.`, modulePath, c.ccfg.ThemesDir))
 					return nil, nil
 				}
 			}
@@ -297,7 +297,7 @@ func (c *collector) add(owner *moduleAdapter, moduleImport Import, disabled bool
 	}
 
 	if found, _ := afero.Exists(c.fs, moduleDir); !found {
-		c.err = c.wrapModuleNotFound(errors.Errorf("%q not found", moduleDir))
+		c.err = c.wrapModuleNotFound(fmt.Errorf("%q not found", moduleDir))
 		return nil, nil
 	}
 
@@ -557,7 +557,7 @@ func (c *collector) collectModulesTXT(owner Module) error {
 		line = strings.TrimSpace(line)
 		parts := strings.Fields(line)
 		if len(parts) != 2 {
-			return errors.Errorf("invalid modules list: %q", filename)
+			return fmt.Errorf("invalid modules list: %q", filename)
 		}
 		path := parts[0]
 
@@ -662,7 +662,7 @@ func (c *collector) normalizeMounts(owner *moduleAdapter, mounts []Mount) ([]Mou
 			targetBase = mnt.Target[0:idxPathSep]
 		}
 		if !files.IsComponentFolder(targetBase) {
-			return nil, errors.Errorf("%s: mount target must be one of: %v", errMsg, files.ComponentFolders)
+			return nil, fmt.Errorf("%s: mount target must be one of: %v", errMsg, files.ComponentFolders)
 		}
 
 		out = append(out, mnt)
@@ -672,7 +672,7 @@ func (c *collector) normalizeMounts(owner *moduleAdapter, mounts []Mount) ([]Mou
 }
 
 func (c *collector) wrapModuleNotFound(err error) error {
-	err = errors.Wrap(ErrNotExist, err.Error())
+	err = fmt.Errorf(err.Error()+": %w", ErrNotExist)
 	if c.GoModulesFilename == "" {
 		return err
 	}
@@ -681,9 +681,9 @@ func (c *collector) wrapModuleNotFound(err error) error {
 
 	switch c.goBinaryStatus {
 	case goBinaryStatusNotFound:
-		return errors.Wrap(err, baseMsg+" you need to install Go to use it. See https://golang.org/dl/.")
+		return fmt.Errorf(baseMsg+" you need to install Go to use it. See https://golang.org/dl/ : %q", err)
 	case goBinaryStatusTooOld:
-		return errors.Wrap(err, baseMsg+" you need to a newer version of Go to use it. See https://golang.org/dl/.")
+		return fmt.Errorf(baseMsg+" you need to a newer version of Go to use it. See https://golang.org/dl/ : %w", err)
 	}
 
 	return err
diff --git a/modules/config.go b/modules/config.go
index 04bf1b422..08154bc11 100644
--- a/modules/config.go
+++ b/modules/config.go
@@ -18,8 +18,6 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/pkg/errors"
-
 	"github.com/gohugoio/hugo/common/hugo"
 
 	"github.com/gohugoio/hugo/config"
@@ -226,7 +224,7 @@ func decodeConfig(cfg config.Provider, pathReplacements map[string]string) (Conf
 			for _, repl := range c.Replacements {
 				parts := strings.Split(repl, "->")
 				if len(parts) != 2 {
-					return c, errors.Errorf(`invalid module.replacements: %q; configure replacement pairs on the form "oldpath->newpath" `, repl)
+					return c, fmt.Errorf(`invalid module.replacements: %q; configure replacement pairs on the form "oldpath->newpath" `, repl)
 				}
 
 				c.replacementsMap[strings.TrimSpace(parts[0])] = strings.TrimSpace(parts[1])
diff --git a/modules/npm/package_builder.go b/modules/npm/package_builder.go
index 911241813..9bdc7eb78 100644
--- a/modules/npm/package_builder.go
+++ b/modules/npm/package_builder.go
@@ -24,8 +24,6 @@ import (
 
 	"github.com/gohugoio/hugo/hugofs/files"
 
-	"github.com/pkg/errors"
-
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/spf13/afero"
 
@@ -57,7 +55,7 @@ func Pack(fs afero.Fs, fis []hugofs.FileMetaInfo) error {
 		if err == nil {
 			// Preserve the original in package.hugo.json.
 			if err = hugio.CopyFile(fs, packageJSONName, files.FilenamePackageHugoJSON); err != nil {
-				return errors.Wrap(err, "npm pack: failed to copy package file")
+				return fmt.Errorf("npm pack: failed to copy package file: %w", err)
 			}
 		} else {
 			// Create one.
@@ -83,7 +81,7 @@ func Pack(fs afero.Fs, fis []hugofs.FileMetaInfo) error {
 	masterFilename := meta.Filename
 	f, err := meta.Open()
 	if err != nil {
-		return errors.Wrap(err, "npm pack: failed to open package file")
+		return fmt.Errorf("npm pack: failed to open package file: %w", err)
 	}
 	b = newPackageBuilder(meta.Module, f)
 	f.Close()
@@ -106,14 +104,14 @@ func Pack(fs afero.Fs, fis []hugofs.FileMetaInfo) error {
 
 		f, err := meta.Open()
 		if err != nil {
-			return errors.Wrap(err, "npm pack: failed to open package file")
+			return fmt.Errorf("npm pack: failed to open package file: %w", err)
 		}
 		b.Add(meta.Module, f)
 		f.Close()
 	}
 
 	if b.Err() != nil {
-		return errors.Wrap(b.Err(), "npm pack: failed to build")
+		return fmt.Errorf("npm pack: failed to build: %w", b.Err())
 	}
 
 	// Replace the dependencies in the original template with the merged set.
@@ -136,11 +134,11 @@ func Pack(fs afero.Fs, fis []hugofs.FileMetaInfo) error {
 	encoder.SetEscapeHTML(false)
 	encoder.SetIndent("", strings.Repeat(" ", 2))
 	if err := encoder.Encode(b.originalPackageJSON); err != nil {
-		return errors.Wrap(err, "npm pack: failed to marshal JSON")
+		return fmt.Errorf("npm pack: failed to marshal JSON: %w", err)
 	}
 
 	if err := afero.WriteFile(fs, packageJSONName, packageJSONData.Bytes(), 0666); err != nil {
-		return errors.Wrap(err, "npm pack: failed to write package.json")
+		return fmt.Errorf("npm pack: failed to write package.json: %w", err)
 	}
 
 	return nil