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, 335 insertions, 0 deletions

diff --git a/modules/config.go b/modules/config.go
new file mode 100644
index 000000000..b084863d4
--- /dev/null
+++ b/modules/config.go
@@ -0,0 +1,335 @@
+// 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 modules
+
+import (
+	"fmt"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"github.com/gohugoio/hugo/common/hugo"
+
+	"github.com/gohugoio/hugo/config"
+	"github.com/gohugoio/hugo/hugofs/files"
+	"github.com/gohugoio/hugo/langs"
+	"github.com/mitchellh/mapstructure"
+)
+
+var DefaultModuleConfig = Config{
+
+	// Default to direct, which means "git clone" and similar. We
+	// will investigate proxy settings in more depth later.
+	// See https://github.com/golang/go/issues/26334
+	Proxy: "direct",
+
+	// Comma separated glob list matching paths that should not use the
+	// proxy configured above.
+	NoProxy: "none",
+
+	// Comma separated glob list matching paths that should be
+	// treated as private.
+	Private: "*.*",
+}
+
+// ApplyProjectConfigDefaults applies default/missing module configuration for
+// the main project.
+func ApplyProjectConfigDefaults(cfg config.Provider, mod Module) error {
+	moda := mod.(*moduleAdapter)
+
+	// Map legacy directory config into the new module.
+	languages := cfg.Get("languagesSortedDefaultFirst").(langs.Languages)
+	isMultiHost := languages.IsMultihost()
+
+	// To bridge between old and new configuration format we need
+	// a way to make sure all of the core components are configured on
+	// the basic level.
+	componentsConfigured := make(map[string]bool)
+	for _, mnt := range moda.mounts {
+		componentsConfigured[mnt.Component()] = true
+	}
+
+	type dirKeyComponent struct {
+		key          string
+		component    string
+		multilingual bool
+	}
+
+	dirKeys := []dirKeyComponent{
+		{"contentDir", files.ComponentFolderContent, true},
+		{"dataDir", files.ComponentFolderData, false},
+		{"layoutDir", files.ComponentFolderLayouts, false},
+		{"i18nDir", files.ComponentFolderI18n, false},
+		{"archetypeDir", files.ComponentFolderArchetypes, false},
+		{"assetDir", files.ComponentFolderAssets, false},
+		{"", files.ComponentFolderStatic, isMultiHost},
+	}
+
+	createMountsFor := func(d dirKeyComponent, cfg config.Provider) []Mount {
+		var lang string
+		if language, ok := cfg.(*langs.Language); ok {
+			lang = language.Lang
+		}
+
+		// Static mounts are a little special.
+		if d.component == files.ComponentFolderStatic {
+			var mounts []Mount
+			staticDirs := getStaticDirs(cfg)
+			if len(staticDirs) > 0 {
+				componentsConfigured[d.component] = true
+			}
+
+			for _, dir := range staticDirs {
+				mounts = append(mounts, Mount{Lang: lang, Source: dir, Target: d.component})
+			}
+
+			return mounts
+
+		}
+
+		if cfg.IsSet(d.key) {
+			source := cfg.GetString(d.key)
+			componentsConfigured[d.component] = true
+
+			return []Mount{Mount{
+				// No lang set for layouts etc.
+				Source: source,
+				Target: d.component}}
+		}
+
+		return nil
+	}
+
+	createMounts := func(d dirKeyComponent) []Mount {
+		var mounts []Mount
+		if d.multilingual {
+			if d.component == files.ComponentFolderContent {
+				seen := make(map[string]bool)
+				hasContentDir := false
+				for _, language := range languages {
+					if language.ContentDir != "" {
+						hasContentDir = true
+						break
+					}
+				}
+
+				if hasContentDir {
+					for _, language := range languages {
+						contentDir := language.ContentDir
+						if contentDir == "" {
+							contentDir = files.ComponentFolderContent
+						}
+						if contentDir == "" || seen[contentDir] {
+							continue
+						}
+						seen[contentDir] = true
+						mounts = append(mounts, Mount{Lang: language.Lang, Source: contentDir, Target: d.component})
+					}
+				}
+
+				componentsConfigured[d.component] = len(seen) > 0
+
+			} else {
+				for _, language := range languages {
+					mounts = append(mounts, createMountsFor(d, language)...)
+				}
+			}
+		} else {
+			mounts = append(mounts, createMountsFor(d, cfg)...)
+		}
+
+		return mounts
+	}
+
+	var mounts []Mount
+	for _, dirKey := range dirKeys {
+		if componentsConfigured[dirKey.component] {
+
+			continue
+		}
+
+		mounts = append(mounts, createMounts(dirKey)...)
+
+	}
+
+	// Add default configuration
+	for _, dirKey := range dirKeys {
+		if componentsConfigured[dirKey.component] {
+			continue
+		}
+		mounts = append(mounts, Mount{Source: dirKey.component, Target: dirKey.component})
+	}
+
+	// Remove duplicates
+	seen := make(map[string]bool)
+	tmp := mounts[:0]
+	for _, m := range mounts {
+		key := path.Join(m.Lang, m.Source, m.Target)
+		if !seen[key] {
+			tmp = append(tmp, m)
+		}
+		seen[key] = true
+	}
+
+	moda.mounts = tmp
+
+	return nil
+}
+
+// DecodeConfig creates a modules Config from a given Hugo configuration.
+func DecodeConfig(cfg config.Provider) (Config, error) {
+	c := DefaultModuleConfig
+
+	if cfg == nil {
+		return c, nil
+	}
+
+	themeSet := cfg.IsSet("theme")
+	moduleSet := cfg.IsSet("module")
+
+	if moduleSet {
+		m := cfg.GetStringMap("module")
+		if err := mapstructure.WeakDecode(m, &c); err != nil {
+			return c, err
+		}
+
+		for i, mnt := range c.Mounts {
+			mnt.Source = filepath.Clean(mnt.Source)
+			mnt.Target = filepath.Clean(mnt.Target)
+			c.Mounts[i] = mnt
+		}
+
+	}
+
+	if themeSet {
+		imports := config.GetStringSlicePreserveString(cfg, "theme")
+		for _, imp := range imports {
+			c.Imports = append(c.Imports, Import{
+				Path: imp,
+			})
+		}
+
+	}
+
+	return c, nil
+}
+
+// Config holds a module config.
+type Config struct {
+	Mounts  []Mount
+	Imports []Import
+
+	// Meta info about this module (license information etc.).
+	Params map[string]interface{}
+
+	// Will be validated against the running Hugo version.
+	HugoVersion HugoVersion
+
+	// Configures GOPROXY.
+	Proxy string
+	// Configures GONOPROXY.
+	NoProxy string
+	// Configures GOPRIVATE.
+	Private string
+}
+
+// HugoVersion holds Hugo binary version requirements for a module.
+type HugoVersion struct {
+	// The minimum Hugo version that this module works with.
+	Min hugo.VersionString
+
+	// The maxium Hugo version that this module works with.
+	Max hugo.VersionString
+
+	// Set if the extended version is needed.
+	Extended bool
+}
+
+func (v HugoVersion) String() string {
+	extended := ""
+	if v.Extended {
+		extended = " extended"
+	}
+
+	if v.Min != "" && v.Max != "" {
+		return fmt.Sprintf("%s/%s%s", v.Min, v.Max, extended)
+	}
+
+	if v.Min != "" {
+		return fmt.Sprintf("Min %s%s", v.Min, extended)
+	}
+
+	if v.Max != "" {
+		return fmt.Sprintf("Max %s%s", v.Max, extended)
+	}
+
+	return extended
+}
+
+// IsValid reports whether this version is valid compared to the running
+// Hugo binary.
+func (v HugoVersion) IsValid() bool {
+	current := hugo.CurrentVersion.Version()
+	if v.Extended && !hugo.IsExtended {
+		return false
+	}
+
+	isValid := true
+
+	if v.Min != "" && current.Compare(v.Min) > 0 {
+		isValid = false
+	}
+
+	if v.Max != "" && current.Compare(v.Max) < 0 {
+		isValid = false
+	}
+
+	return isValid
+}
+
+type Import struct {
+	Path         string // Module path
+	IgnoreConfig bool   // Ignore any config.toml found.
+	Disabled     bool   // Turn off this module.
+	Mounts       []Mount
+}
+
+type Mount struct {
+	Source string // relative path in source repo, e.g. "scss"
+	Target string // relative target path, e.g. "assets/bootstrap/scss"
+
+	Lang string // any language code associated with this mount.
+}
+
+func (m Mount) Component() string {
+	return strings.Split(m.Target, fileSeparator)[0]
+}
+
+func getStaticDirs(cfg config.Provider) []string {
+	var staticDirs []string
+	for i := -1; i <= 10; i++ {
+		staticDirs = append(staticDirs, getStringOrStringSlice(cfg, "staticDir", i)...)
+	}
+	return staticDirs
+}
+
+func getStringOrStringSlice(cfg config.Provider, key string, id int) []string {
+
+	if id >= 0 {
+		key = fmt.Sprintf("%s%d", key, id)
+	}
+
+	return config.GetStringSlicePreserveString(cfg, key)
+
+}