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

1 files changed, 293 insertions, 0 deletions

diff --git a/hugofs/slice_fs.go b/hugofs/slice_fs.go
new file mode 100644
index 000000000..4fb026ab2
--- /dev/null
+++ b/hugofs/slice_fs.go
@@ -0,0 +1,293 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hugofs
+
+import (
+	"os"
+	"syscall"
+	"time"
+
+	"github.com/pkg/errors"
+
+	"github.com/spf13/afero"
+)
+
+var (
+	_ afero.Fs      = (*SliceFs)(nil)
+	_ afero.Lstater = (*SliceFs)(nil)
+	_ afero.File    = (*sliceDir)(nil)
+)
+
+func NewSliceFs(dirs ...FileMetaInfo) (afero.Fs, error) {
+	if len(dirs) == 0 {
+		return NoOpFs, nil
+	}
+
+	for _, dir := range dirs {
+		if !dir.IsDir() {
+			return nil, errors.New("this fs supports directories only")
+		}
+	}
+
+	fs := &SliceFs{
+		dirs: dirs,
+	}
+
+	return fs, nil
+
+}
+
+// SliceFs is an ordered composite filesystem.
+type SliceFs struct {
+	dirs []FileMetaInfo
+}
+
+func (fs *SliceFs) Chmod(n string, m os.FileMode) error {
+	return syscall.EPERM
+}
+
+func (fs *SliceFs) Chtimes(n string, a, m time.Time) error {
+	return syscall.EPERM
+}
+
+func (fs *SliceFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
+	fi, _, err := fs.pickFirst(name)
+
+	if err != nil {
+		return nil, false, err
+	}
+
+	if fi.IsDir() {
+		return decorateFileInfo(fi, fs, fs.getOpener(name), "", "", nil), false, nil
+	}
+
+	return nil, false, errors.Errorf("lstat: files not supported: %q", name)
+
+}
+
+func (fs *SliceFs) Mkdir(n string, p os.FileMode) error {
+	return syscall.EPERM
+}
+
+func (fs *SliceFs) MkdirAll(n string, p os.FileMode) error {
+	return syscall.EPERM
+}
+
+func (fs *SliceFs) Name() string {
+	return "SliceFs"
+}
+
+func (fs *SliceFs) Open(name string) (afero.File, error) {
+	fi, idx, err := fs.pickFirst(name)
+	if err != nil {
+		return nil, err
+	}
+
+	if !fi.IsDir() {
+		panic("currently only dirs in here")
+	}
+
+	return &sliceDir{
+		lfs:     fs,
+		idx:     idx,
+		dirname: name,
+	}, nil
+
+}
+
+func (fs *SliceFs) OpenFile(name string, flag int, perm os.FileMode) (afero.File, error) {
+	panic("not implemented")
+}
+
+func (fs *SliceFs) ReadDir(name string) ([]os.FileInfo, error) {
+	panic("not implemented")
+}
+
+func (fs *SliceFs) Remove(n string) error {
+	return syscall.EPERM
+}
+
+func (fs *SliceFs) RemoveAll(p string) error {
+	return syscall.EPERM
+}
+
+func (fs *SliceFs) Rename(o, n string) error {
+	return syscall.EPERM
+}
+
+func (fs *SliceFs) Stat(name string) (os.FileInfo, error) {
+	fi, _, err := fs.LstatIfPossible(name)
+	return fi, err
+}
+
+func (fs *SliceFs) Create(n string) (afero.File, error) {
+	return nil, syscall.EPERM
+}
+
+func (fs *SliceFs) getOpener(name string) func() (afero.File, error) {
+	return func() (afero.File, error) {
+		return fs.Open(name)
+	}
+}
+
+func (fs *SliceFs) pickFirst(name string) (os.FileInfo, int, error) {
+	for i, mfs := range fs.dirs {
+		meta := mfs.Meta()
+		fs := meta.Fs()
+		fi, _, err := lstatIfPossible(fs, name)
+		if err == nil {
+			// Gotta match!
+			return fi, i, nil
+		}
+
+		if !os.IsNotExist(err) {
+			// Real error
+			return nil, -1, err
+		}
+	}
+
+	// Not found
+	return nil, -1, os.ErrNotExist
+}
+
+func (fs *SliceFs) readDirs(name string, startIdx, count int) ([]os.FileInfo, error) {
+	collect := func(lfs FileMeta) ([]os.FileInfo, error) {
+		d, err := lfs.Fs().Open(name)
+		if err != nil {
+			if !os.IsNotExist(err) {
+				return nil, err
+			}
+			return nil, nil
+		} else {
+			defer d.Close()
+			dirs, err := d.Readdir(-1)
+			if err != nil {
+				return nil, err
+			}
+			return dirs, nil
+		}
+	}
+
+	var dirs []os.FileInfo
+
+	for i := startIdx; i < len(fs.dirs); i++ {
+		mfs := fs.dirs[i]
+
+		fis, err := collect(mfs.Meta())
+		if err != nil {
+			return nil, err
+		}
+
+		dirs = append(dirs, fis...)
+
+	}
+
+	seen := make(map[string]bool)
+	var duplicates []int
+	for i, fi := range dirs {
+		if !fi.IsDir() {
+			continue
+		}
+
+		if seen[fi.Name()] {
+			duplicates = append(duplicates, i)
+		} else {
+			// Make sure it's opened by this filesystem.
+			dirs[i] = decorateFileInfo(fi, fs, fs.getOpener(fi.(FileMetaInfo).Meta().Filename()), "", "", nil)
+			seen[fi.Name()] = true
+		}
+	}
+
+	// Remove duplicate directories, keep first.
+	if len(duplicates) > 0 {
+		for i := len(duplicates) - 1; i >= 0; i-- {
+			idx := duplicates[i]
+			dirs = append(dirs[:idx], dirs[idx+1:]...)
+		}
+	}
+
+	if count > 0 && len(dirs) >= count {
+		return dirs[:count], nil
+	}
+
+	return dirs, nil
+
+}
+
+type sliceDir struct {
+	lfs     *SliceFs
+	idx     int
+	dirname string
+}
+
+func (f *sliceDir) Close() error {
+	return nil
+}
+
+func (f *sliceDir) Name() string {
+	return f.dirname
+}
+
+func (f *sliceDir) Read(p []byte) (n int, err error) {
+	panic("not implemented")
+}
+
+func (f *sliceDir) ReadAt(p []byte, off int64) (n int, err error) {
+	panic("not implemented")
+}
+
+func (f *sliceDir) Readdir(count int) ([]os.FileInfo, error) {
+	return f.lfs.readDirs(f.dirname, f.idx, count)
+}
+
+func (f *sliceDir) Readdirnames(count int) ([]string, error) {
+	dirsi, err := f.Readdir(count)
+	if err != nil {
+		return nil, err
+	}
+
+	dirs := make([]string, len(dirsi))
+	for i, d := range dirsi {
+		dirs[i] = d.Name()
+	}
+	return dirs, nil
+}
+
+func (f *sliceDir) Seek(offset int64, whence int) (int64, error) {
+	panic("not implemented")
+}
+
+func (f *sliceDir) Stat() (os.FileInfo, error) {
+	panic("not implemented")
+}
+
+func (f *sliceDir) Sync() error {
+	panic("not implemented")
+}
+
+func (f *sliceDir) Truncate(size int64) error {
+	panic("not implemented")
+}
+
+func (f *sliceDir) Write(p []byte) (n int, err error) {
+	panic("not implemented")
+}
+
+func (f *sliceDir) WriteAt(p []byte, off int64) (n int, err error) {
+	panic("not implemented")
+}
+
+func (f *sliceDir) WriteString(s string) (ret int, err error) {
+	panic("not implemented")
+}