Add Hugo Modules

This commit implements Hugo Modules.

This is a broad subject, but some keywords include:

* A new `module` configuration section where you can import almost anything. You can configure both your own file mounts nd the file mounts of the modules you import. This is the new recommended way of configuring what you earlier put in `configDir`, `staticDir` etc. And it also allows you to mount folders in non-Hugo-projects, e.g. the `SCSS` folder in the Bootstrap GitHub project.
* A module consists of a set of mounts to the standard 7 component types in Hugo: `static`, `content`, `layouts`, `data`, `assets`, `i18n`, and `archetypes`. Yes, Theme Components can now include content, which should be very useful, especially in bigger multilingual projects.
* Modules not in your local file cache will be downloaded automatically and even "hot replaced" while the server is running.
* Hugo Modules supports and encourages semver versioned modules, and uses the minimal version selection algorithm to resolve versions.
* A new set of CLI commands are provided to manage all of this: `hugo mod init`,  `hugo mod get`,  `hugo mod graph`,  `hugo mod tidy`, and  `hugo mod vendor`.

All of the above is backed by Go Modules.

Fixes #5973
Fixes #5996
Fixes #6010
Fixes #5911
Fixes #5940
Fixes #6074
Fixes #6082
Fixes #6092

helpers/path.go

@@ -26,6 +26,8 @@ import (
 
 	"github.com/gohugoio/hugo/config"
 
+	"github.com/gohugoio/hugo/hugofs"
+
 	"github.com/gohugoio/hugo/common/hugio"
 	_errors "github.com/pkg/errors"
 	"github.com/spf13/afero"
@@ -172,32 +174,6 @@ func ReplaceExtension(path string, newExt string) string {
 	return f + "." + newExt
 }
 
-// GetFirstThemeDir gets the root directory of the first theme, if there is one.
-// If there is no theme, returns the empty string.
-func (p *PathSpec) GetFirstThemeDir() string {
-	if p.ThemeSet() {
-		return p.AbsPathify(filepath.Join(p.ThemesDir, p.Themes()[0]))
-	}
-	return ""
-}
-
-// GetThemesDir gets the absolute root theme dir path.
-func (p *PathSpec) GetThemesDir() string {
-	if p.ThemeSet() {
-		return p.AbsPathify(p.ThemesDir)
-	}
-	return ""
-}
-
-// GetRelativeThemeDir gets the relative root directory of the current theme, if there is one.
-// If there is no theme, returns the empty string.
-func (p *PathSpec) GetRelativeThemeDir() string {
-	if p.ThemeSet() {
-		return strings.TrimPrefix(filepath.Join(p.ThemesDir, p.Themes()[0]), FilePathSeparator)
-	}
-	return ""
-}
-
 func makePathRelative(inPath string, possibleDirectories ...string) (string, error) {
 
 	for _, currentPath := range possibleDirectories {
@@ -379,6 +355,107 @@ func prettifyPath(in string, b filepathPathBridge) string {
 	return b.Join(b.Dir(in), name, "index"+ext)
 }
 
+type NamedSlice struct {
+	Name  string
+	Slice []string
+}
+
+func (n NamedSlice) String() string {
+	if len(n.Slice) == 0 {
+		return n.Name
+	}
+	return fmt.Sprintf("%s%s{%s}", n.Name, FilePathSeparator, strings.Join(n.Slice, ","))
+}
+
+func ExtractAndGroupRootPaths(paths []string) []NamedSlice {
+	if len(paths) == 0 {
+		return nil
+	}
+
+	pathsCopy := make([]string, len(paths))
+	hadSlashPrefix := strings.HasPrefix(paths[0], FilePathSeparator)
+
+	for i, p := range paths {
+		pathsCopy[i] = strings.Trim(filepath.ToSlash(p), "/")
+	}
+
+	sort.Strings(pathsCopy)
+
+	pathsParts := make([][]string, len(pathsCopy))
+
+	for i, p := range pathsCopy {
+		pathsParts[i] = strings.Split(p, "/")
+	}
+
+	var groups [][]string
+
+	for i, p1 := range pathsParts {
+		c1 := -1
+
+		for j, p2 := range pathsParts {
+			if i == j {
+				continue
+			}
+
+			c2 := -1
+
+			for i, v := range p1 {
+				if i >= len(p2) {
+					break
+				}
+				if v != p2[i] {
+					break
+				}
+
+				c2 = i
+			}
+
+			if c1 == -1 || (c2 != -1 && c2 < c1) {
+				c1 = c2
+			}
+		}
+
+		if c1 != -1 {
+			groups = append(groups, p1[:c1+1])
+		} else {
+			groups = append(groups, p1)
+		}
+	}
+
+	groupsStr := make([]string, len(groups))
+	for i, g := range groups {
+		groupsStr[i] = strings.Join(g, "/")
+	}
+
+	groupsStr = UniqueStringsSorted(groupsStr)
+
+	var result []NamedSlice
+
+	for _, g := range groupsStr {
+		name := filepath.FromSlash(g)
+		if hadSlashPrefix {
+			name = FilePathSeparator + name
+		}
+		ns := NamedSlice{Name: name}
+		for _, p := range pathsCopy {
+			if !strings.HasPrefix(p, g) {
+				continue
+			}
+
+			p = strings.TrimPrefix(p, g)
+			if p != "" {
+				ns.Slice = append(ns.Slice, p)
+			}
+		}
+
+		ns.Slice = UniqueStrings(ExtractRootPaths(ns.Slice))
+
+		result = append(result, ns)
+	}
+
+	return result
+}
+
 // ExtractRootPaths extracts the root paths from the supplied list of paths.
 // The resulting root path will not contain any file separators, but there
 // may be duplicates.
@@ -425,98 +502,21 @@ func FindCWD() (string, error) {
 	return path, nil
 }
 
-// SymbolicWalk is like filepath.Walk, but it supports the root being a
-// symbolic link. It will still not follow symbolic links deeper down in
-// the file structure.
-func SymbolicWalk(fs afero.Fs, root string, walker filepath.WalkFunc) error {
-
-	// Sanity check
-	if root != "" && len(root) < 4 {
-		return errors.New("path is too short")
+// SymbolicWalk is like filepath.Walk, but it follows symbolic links.
+func SymbolicWalk(fs afero.Fs, root string, walker hugofs.WalkFunc) error {
+	if _, isOs := fs.(*afero.OsFs); isOs {
+		// Mainly to track symlinks.
+		fs = hugofs.NewBaseFileDecorator(fs)
 	}
 
-	// Handle the root first
-	fileInfo, realPath, err := getRealFileInfo(fs, root)
+	w := hugofs.NewWalkway(hugofs.WalkwayConfig{
+		Fs:     fs,
+		Root:   root,
+		WalkFn: walker,
+	})
 
-	if err != nil {
-		return walker(root, nil, err)
-	}
+	return w.Walk()
 
-	if !fileInfo.IsDir() {
-		return fmt.Errorf("cannot walk regular file %s", root)
-	}
-
-	if err := walker(realPath, fileInfo, err); err != nil && err != filepath.SkipDir {
-		return err
-	}
-
-	// Some of Hugo's filesystems represents an ordered root folder, i.e. project first, then theme folders.
-	// Make sure that order is preserved. afero.Walk will sort the directories down in the file tree,
-	// but we don't care about that.
-	rootContent, err := readDir(fs, root, false)
-
-	if err != nil {
-		return walker(root, nil, err)
-	}
-
-	for _, fi := range rootContent {
-		if err := afero.Walk(fs, filepath.Join(root, fi.Name()), walker); err != nil {
-			return err
-		}
-	}
-
-	return nil
-
-}
-
-func readDir(fs afero.Fs, dirname string, doSort bool) ([]os.FileInfo, error) {
-	f, err := fs.Open(dirname)
-	if err != nil {
-		return nil, err
-	}
-	list, err := f.Readdir(-1)
-	f.Close()
-	if err != nil {
-		return nil, err
-	}
-	if doSort {
-		sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() })
-	}
-	return list, nil
-}
-
-func getRealFileInfo(fs afero.Fs, path string) (os.FileInfo, string, error) {
-	fileInfo, err := LstatIfPossible(fs, path)
-	realPath := path
-
-	if err != nil {
-		return nil, "", err
-	}
-
-	if fileInfo.Mode()&os.ModeSymlink == os.ModeSymlink {
-		link, err := filepath.EvalSymlinks(path)
-		if err != nil {
-			return nil, "", _errors.Wrapf(err, "Cannot read symbolic link %q", path)
-		}
-		fileInfo, err = LstatIfPossible(fs, link)
-		if err != nil {
-			return nil, "", _errors.Wrapf(err, "Cannot stat %q", link)
-		}
-		realPath = link
-	}
-	return fileInfo, realPath, nil
-}
-
-// GetRealPath returns the real file path for the given path, whether it is a
-// symlink or not.
-func GetRealPath(fs afero.Fs, path string) (string, error) {
-	_, realPath, err := getRealFileInfo(fs, path)
-
-	if err != nil {
-		return "", err
-	}
-
-	return realPath, nil
 }
 
 // LstatIfPossible can be used to call Lstat if possible, else Stat.