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

43 files changed, 3009 insertions, 3447 deletions

diff --git a/hugolib/config.go b/hugolib/config.go
index 50e4ca6ec..b7ac46171 100644
--- a/hugolib/config.go
+++ b/hugolib/config.go
@@ -14,21 +14,24 @@
 package hugolib
 
 import (
-	"fmt"
-
 	"os"
 	"path/filepath"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/loggers"
+
+	"github.com/gohugoio/hugo/cache/filecache"
+
+	"github.com/gohugoio/hugo/common/maps"
+
 	"github.com/gohugoio/hugo/parser/metadecoders"
 
 	"github.com/gohugoio/hugo/common/herrors"
 	"github.com/gohugoio/hugo/common/hugo"
 	"github.com/gohugoio/hugo/hugolib/paths"
-	"github.com/pkg/errors"
-	_errors "github.com/pkg/errors"
-
 	"github.com/gohugoio/hugo/langs"
+	"github.com/gohugoio/hugo/modules"
+	"github.com/pkg/errors"
 
 	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/config/privacy"
@@ -67,7 +70,8 @@ func loadSiteConfig(cfg config.Provider) (scfg SiteConfig, err error) {
 
 // ConfigSourceDescriptor describes where to find the config (e.g. config.toml etc.).
 type ConfigSourceDescriptor struct {
-	Fs afero.Fs
+	Fs     afero.Fs
+	Logger *loggers.Logger
 
 	// Path to the config file to use, e.g. /my/project/config.toml
 	Filename string
@@ -84,6 +88,9 @@ type ConfigSourceDescriptor struct {
 
 	// production, development
 	Environment string
+
+	// Defaults to os.Environ if not set.
+	Environ []string
 }
 
 func (d ConfigSourceDescriptor) configFilenames() []string {
@@ -111,51 +118,43 @@ var ErrNoConfigFile = errors.New("Unable to locate config file or config directo
 // LoadConfig loads Hugo configuration into a new Viper and then adds
 // a set of defaults.
 func LoadConfig(d ConfigSourceDescriptor, doWithConfig ...func(cfg config.Provider) error) (*viper.Viper, []string, error) {
+
 	if d.Environment == "" {
 		d.Environment = hugo.EnvironmentProduction
 	}
 
+	if len(d.Environ) == 0 {
+		d.Environ = os.Environ()
+	}
+
 	var configFiles []string
 
 	v := viper.New()
 	l := configLoader{ConfigSourceDescriptor: d}
 
-	v.AutomaticEnv()
-	v.SetEnvPrefix("hugo")
-
-	var cerr error
-
 	for _, name := range d.configFilenames() {
 		var filename string
-		if filename, cerr = l.loadConfig(name, v); cerr != nil && cerr != ErrNoConfigFile {
-			return nil, nil, cerr
+		filename, err := l.loadConfig(name, v)
+		if err == nil {
+			configFiles = append(configFiles, filename)
+		} else if err != ErrNoConfigFile {
+			return nil, nil, err
 		}
-		configFiles = append(configFiles, filename)
 	}
 
 	if d.AbsConfigDir != "" {
 		dirnames, err := l.loadConfigFromConfigDir(v)
 		if err == nil {
 			configFiles = append(configFiles, dirnames...)
+		} else if err != ErrNoConfigFile {
+			return nil, nil, err
 		}
-		cerr = err
 	}
 
 	if err := loadDefaultSettingsFor(v); err != nil {
 		return v, configFiles, err
 	}
 
-	if cerr == nil {
-		themeConfigFiles, err := l.loadThemeConfig(v)
-		if err != nil {
-			return v, configFiles, err
-		}
-
-		if len(themeConfigFiles) > 0 {
-			configFiles = append(configFiles, themeConfigFiles...)
-		}
-	}
-
 	// We create languages based on the settings, so we need to make sure that
 	// all configuration is loaded/set before doing that.
 	for _, d := range doWithConfig {
@@ -164,12 +163,75 @@ func LoadConfig(d ConfigSourceDescriptor, doWithConfig ...func(cfg config.Provid
 		}
 	}
 
+	// Apply environment overrides
+	if len(d.Environ) > 0 {
+		// Extract all that start with the HUGO_ prefix
+		const hugoEnvPrefix = "HUGO_"
+		var hugoEnv []string
+		for _, v := range d.Environ {
+			key, val := config.SplitEnvVar(v)
+			if strings.HasPrefix(key, hugoEnvPrefix) {
+				hugoEnv = append(hugoEnv, strings.ToLower(strings.TrimPrefix(key, hugoEnvPrefix)), val)
+			}
+		}
+
+		if len(hugoEnv) > 0 {
+			for i := 0; i < len(hugoEnv); i += 2 {
+				key, valStr := strings.ToLower(hugoEnv[i]), hugoEnv[i+1]
+
+				existing, nestedKey, owner, err := maps.GetNestedParamFn(key, "_", v.Get)
+				if err != nil {
+					return v, configFiles, err
+				}
+
+				if existing != nil {
+					val, err := metadecoders.Default.UnmarshalStringTo(valStr, existing)
+					if err != nil {
+						continue
+					}
+
+					if owner != nil {
+						owner[nestedKey] = val
+					} else {
+						v.Set(key, val)
+					}
+				} else {
+					v.Set(key, valStr)
+				}
+			}
+		}
+	}
+
+	modulesConfig, err := l.loadModulesConfig(v)
+	if err != nil {
+		return v, configFiles, err
+	}
+
+	mods, modulesConfigFiles, err := l.collectModules(modulesConfig, v)
+	if err != nil {
+		return v, configFiles, err
+	}
+
 	if err := loadLanguageSettings(v, nil); err != nil {
 		return v, configFiles, err
 	}
 
-	return v, configFiles, cerr
+	// Apply default project mounts.
+	if err := modules.ApplyProjectConfigDefaults(v, mods[len(mods)-1]); err != nil {
+		return v, configFiles, err
+	}
+
+	if len(modulesConfigFiles) > 0 {
+		configFiles = append(configFiles, modulesConfigFiles...)
+	}
 
+	return v, configFiles, nil
+
+}
+
+func loadLanguageSettings(cfg config.Provider, oldLangs langs.Languages) error {
+	_, err := langs.LoadLanguageSettings(cfg, oldLangs)
+	return err
 }
 
 type configLoader struct {
@@ -334,145 +396,79 @@ func (l configLoader) loadConfigFromConfigDir(v *viper.Viper) ([]string, error)
 	return dirnames, nil
 }
 
-func loadLanguageSettings(cfg config.Provider, oldLangs langs.Languages) error {
+func (l configLoader) loadModulesConfig(v1 *viper.Viper) (modules.Config, error) {
 
-	defaultLang := cfg.GetString("defaultContentLanguage")
-
-	var languages map[string]interface{}
-
-	languagesFromConfig := cfg.GetStringMap("languages")
-	disableLanguages := cfg.GetStringSlice("disableLanguages")
-
-	if len(disableLanguages) == 0 {
-		languages = languagesFromConfig
-	} else {
-		languages = make(map[string]interface{})
-		for k, v := range languagesFromConfig {
-			for _, disabled := range disableLanguages {
-				if disabled == defaultLang {
-					return fmt.Errorf("cannot disable default language %q", defaultLang)
-				}
-
-				if strings.EqualFold(k, disabled) {
-					v.(map[string]interface{})["disabled"] = true
-					break
-				}
-			}
-			languages[k] = v
-		}
-	}
-
-	var (
-		languages2 langs.Languages
-		err        error
-	)
-
-	if len(languages) == 0 {
-		languages2 = append(languages2, langs.NewDefaultLanguage(cfg))
-	} else {
-		languages2, err = toSortedLanguages(cfg, languages)
-		if err != nil {
-			return _errors.Wrap(err, "Failed to parse multilingual config")
-		}
-	}
-
-	if oldLangs != nil {
-		// When in multihost mode, the languages are mapped to a server, so
-		// some structural language changes will need a restart of the dev server.
-		// The validation below isn't complete, but should cover the most
-		// important cases.
-		var invalid bool
-		if languages2.IsMultihost() != oldLangs.IsMultihost() {
-			invalid = true
-		} else {
-			if languages2.IsMultihost() && len(languages2) != len(oldLangs) {
-				invalid = true
-			}
-		}
-
-		if invalid {
-			return errors.New("language change needing a server restart detected")
-		}
-
-		if languages2.IsMultihost() {
-			// We need to transfer any server baseURL to the new language
-			for i, ol := range oldLangs {
-				nl := languages2[i]
-				nl.Set("baseURL", ol.GetString("baseURL"))
-			}
-		}
+	modConfig, err := modules.DecodeConfig(v1)
+	if err != nil {
+		return modules.Config{}, err
 	}
 
-	// The defaultContentLanguage is something the user has to decide, but it needs
-	// to match a language in the language definition list.
-	langExists := false
-	for _, lang := range languages2 {
-		if lang.Lang == defaultLang {
-			langExists = true
-			break
-		}
-	}
+	return modConfig, nil
+}
 
-	if !langExists {
-		return fmt.Errorf("site config value %q for defaultContentLanguage does not match any language definition", defaultLang)
+func (l configLoader) collectModules(modConfig modules.Config, v1 *viper.Viper) (modules.Modules, []string, error) {
+	workingDir := l.WorkingDir
+	if workingDir == "" {
+		workingDir = v1.GetString("workingDir")
 	}
 
-	cfg.Set("languagesSorted", languages2)
-	cfg.Set("multilingual", len(languages2) > 1)
+	themesDir := paths.AbsPathify(l.WorkingDir, v1.GetString("themesDir"))
 
-	multihost := languages2.IsMultihost()
-
-	if multihost {
-		cfg.Set("defaultContentLanguageInSubdir", true)
-		cfg.Set("multihost", true)
-	}
-
-	if multihost {
-		// The baseURL may be provided at the language level. If that is true,
-		// then every language must have a baseURL. In this case we always render
-		// to a language sub folder, which is then stripped from all the Permalink URLs etc.
-		for _, l := range languages2 {
-			burl := l.GetLocal("baseURL")
-			if burl == nil {
-				return errors.New("baseURL must be set on all or none of the languages")
-			}
-		}
+	ignoreVendor := v1.GetBool("ignoreVendor")
 
+	filecacheConfigs, err := filecache.DecodeConfig(l.Fs, v1)
+	if err != nil {
+		return nil, nil, err
 	}
+	v1.Set("filecacheConfigs", filecacheConfigs)
 
-	return nil
-}
+	modulesClient := modules.NewClient(modules.ClientConfig{
+		Fs:           l.Fs,
+		Logger:       l.Logger,
+		WorkingDir:   workingDir,
+		ThemesDir:    themesDir,
+		CacheDir:     filecacheConfigs.CacheDirModules(),
+		ModuleConfig: modConfig,
+		IgnoreVendor: ignoreVendor,
+	})
 
-func (l configLoader) loadThemeConfig(v1 *viper.Viper) ([]string, error) {
-	themesDir := paths.AbsPathify(l.WorkingDir, v1.GetString("themesDir"))
-	themes := config.GetStringSlicePreserveString(v1, "theme")
+	v1.Set("modulesClient", modulesClient)
 
-	themeConfigs, err := paths.CollectThemes(l.Fs, themesDir, themes)
+	moduleConfig, err := modulesClient.Collect()
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
-	if len(themeConfigs) == 0 {
-		return nil, nil
-	}
+	// Avoid recreating these later.
+	v1.Set("allModules", moduleConfig.ActiveModules)
 
-	v1.Set("allThemes", themeConfigs)
+	if len(moduleConfig.ActiveModules) == 0 {
+		return nil, nil, nil
+	}
 
 	var configFilenames []string
-	for _, tc := range themeConfigs {
-		if tc.ConfigFilename != "" {
-			configFilenames = append(configFilenames, tc.ConfigFilename)
+	for _, tc := range moduleConfig.ActiveModules {
+		if tc.ConfigFilename() != "" {
+			if tc.Watch() {
+				configFilenames = append(configFilenames, tc.ConfigFilename())
+			}
 			if err := l.applyThemeConfig(v1, tc); err != nil {
-				return nil, err
+				return nil, nil, err
 			}
 		}
 	}
 
-	return configFilenames, nil
+	if moduleConfig.GoModulesFilename != "" {
+		// We want to watch this for changes and trigger rebuild on version
+		// changes etc.
+		configFilenames = append(configFilenames, moduleConfig.GoModulesFilename)
+	}
+
+	return moduleConfig.ActiveModules, configFilenames, nil
 
 }
 
-func (l configLoader) applyThemeConfig(v1 *viper.Viper, theme paths.ThemeConfig) error {
+func (l configLoader) applyThemeConfig(v1 *viper.Viper, theme modules.Module) error {
 
 	const (
 		paramsKey    = "params"
@@ -480,22 +476,12 @@ func (l configLoader) applyThemeConfig(v1 *viper.Viper, theme paths.ThemeConfig)
 		menuKey      = "menus"
 	)
 
-	v2 := theme.Cfg
+	v2 := theme.Cfg()
 
 	for _, key := range []string{paramsKey, "outputformats", "mediatypes"} {
 		l.mergeStringMapKeepLeft("", key, v1, v2)
 	}
 
-	themeLower := strings.ToLower(theme.Name)
-	themeParamsNamespace := paramsKey + "." + themeLower
-
-	// Set namespaced params
-	if v2.IsSet(paramsKey) && !v1.IsSet(themeParamsNamespace) {
-		// Set it in the default store to make sure it gets in the same or
-		// behind the others.
-		v1.SetDefault(themeParamsNamespace, v2.Get(paramsKey))
-	}
-
 	// Only add params and new menu entries, we do not add language definitions.
 	if v1.IsSet(languagesKey) && v2.IsSet(languagesKey) {
 		v1Langs := v1.GetStringMap(languagesKey)
@@ -508,12 +494,6 @@ func (l configLoader) applyThemeConfig(v1 *viper.Viper, theme paths.ThemeConfig)
 			if k == "" {
 				continue
 			}
-			langParamsKey := languagesKey + "." + k + "." + paramsKey
-			langParamsThemeNamespace := langParamsKey + "." + themeLower
-			// Set namespaced params
-			if v2.IsSet(langParamsKey) && !v1.IsSet(langParamsThemeNamespace) {
-				v1.SetDefault(langParamsThemeNamespace, v2.Get(langParamsKey))
-			}
 
 			langMenuKey := languagesKey + "." + k + "." + menuKey
 			if v2.IsSet(langMenuKey) {
@@ -577,18 +557,23 @@ func loadDefaultSettingsFor(v *viper.Viper) error {
 
 	v.RegisterAlias("indexes", "taxonomies")
 
+	/*
+
+		TODO(bep) from 0.56 these are configured as module mounts.
+			v.SetDefault("contentDir", "content")
+			v.SetDefault("layoutDir", "layouts")
+			v.SetDefault("assetDir", "assets")
+			v.SetDefault("staticDir", "static")
+			v.SetDefault("dataDir", "data")
+			v.SetDefault("i18nDir", "i18n")
+			v.SetDefault("archetypeDir", "archetypes")
+	*/
+
 	v.SetDefault("cleanDestinationDir", false)
 	v.SetDefault("watch", false)
 	v.SetDefault("metaDataFormat", "toml")
-	v.SetDefault("contentDir", "content")
-	v.SetDefault("layoutDir", "layouts")
-	v.SetDefault("assetDir", "assets")
-	v.SetDefault("staticDir", "static")
 	v.SetDefault("resourceDir", "resources")
-	v.SetDefault("archetypeDir", "archetypes")
 	v.SetDefault("publishDir", "public")
-	v.SetDefault("dataDir", "data")
-	v.SetDefault("i18nDir", "i18n")
 	v.SetDefault("themesDir", "themes")
 	v.SetDefault("buildDrafts", false)
 	v.SetDefault("buildFuture", false)
@@ -635,5 +620,6 @@ func loadDefaultSettingsFor(v *viper.Viper) error {
 	v.SetDefault("disableFastRender", false)
 	v.SetDefault("timeout", 10000) // 10 seconds
 	v.SetDefault("enableInlineShortcodes", false)
+
 	return nil
 }
diff --git a/hugolib/config_test.go b/hugolib/config_test.go
index 885a07ee9..bd980235f 100644
--- a/hugolib/config_test.go
+++ b/hugolib/config_test.go
@@ -14,6 +14,9 @@
 package hugolib
 
 import (
+	"bytes"
+	"fmt"
+	"path/filepath"
 	"testing"
 
 	"github.com/spf13/afero"
@@ -40,10 +43,7 @@ func TestLoadConfig(t *testing.T) {
 	require.NoError(t, err)
 
 	assert.Equal("side", cfg.GetString("paginatePath"))
-	// default
-	assert.Equal("layouts", cfg.GetString("layoutDir"))
-	// no themes
-	assert.False(cfg.IsSet("allThemes"))
+
 }
 
 func TestLoadMultiConfig(t *testing.T) {
@@ -188,11 +188,6 @@ map[string]interface {}{
   "p1": "p1 main",
   "p2": "p2 main",
   "p3": "p3 theme",
-  "test-theme": map[string]interface {}{
-    "p1": "p1 theme",
-    "p2": "p2 theme",
-    "p3": "p3 theme",
-  },
   "top": "top",
 }`, got["params"])
 
@@ -257,10 +252,6 @@ map[string]interface {}{
     "params": map[string]interface {}{
       "pl1": "p1-en-main",
       "pl2": "p2-en-theme",
-      "test-theme": map[string]interface {}{
-        "pl1": "p1-en-theme",
-        "pl2": "p2-en-theme",
-      },
     },
   },
   "nb": map[string]interface {}{
@@ -275,11 +266,6 @@ map[string]interface {}{
     "params": map[string]interface {}{
       "pl1": "p1-nb-main",
       "pl2": "p2-nb-theme",
-      "test-theme": map[string]interface {}{
-        "pl1": "p1-nb-theme",
-        "pl2": "p2-nb-theme",
-        "top": "top-nb-theme",
-      },
     },
   },
 }
@@ -397,3 +383,142 @@ privacyEnhanced = true
 	assert.True(b.H.Sites[0].Info.Config().Privacy.YouTube.PrivacyEnhanced)
 
 }
+
+func TestLoadConfigModules(t *testing.T) {
+	t.Parallel()
+
+	assert := require.New(t)
+
+	// https://github.com/gohugoio/hugoThemes#themetoml
+
+	const (
+		// Before Hugo 0.56 each theme/component could have its own theme.toml
+		// with some settings, mostly used on the Hugo themes site.
+		// To preserve combability we read these files into the new "modules"
+		// section in config.toml.
+		o1t = `
+name = "Component o1"
+license = "MIT"
+min_version = 0.38
+`
+		// This is the component's config.toml, using the old theme syntax.
+		o1c = `
+theme = ["n2"]
+`
+
+		n1 = `
+title = "Component n1"
+
+[module]
+description = "Component n1 description"
+[module.hugoVersion]
+min = "0.40.0"
+max = "0.50.0"
+extended = true
+[[module.imports]]
+path="o1"
+[[module.imports]]
+path="n3"
+
+
+`
+
+		n2 = `
+title = "Component n2"
+`
+
+		n3 = `
+title = "Component n3"
+`
+
+		n4 = `
+title = "Component n4"
+`
+	)
+
+	b := newTestSitesBuilder(t)
+
+	writeThemeFiles := func(name, configTOML, themeTOML string) {
+		b.WithSourceFile(filepath.Join("themes", name, "data", "module.toml"), fmt.Sprintf("name=%q", name))
+		if configTOML != "" {
+			b.WithSourceFile(filepath.Join("themes", name, "config.toml"), configTOML)
+		}
+		if themeTOML != "" {
+			b.WithSourceFile(filepath.Join("themes", name, "theme.toml"), themeTOML)
+		}
+	}
+
+	writeThemeFiles("n1", n1, "")
+	writeThemeFiles("n2", n2, "")
+	writeThemeFiles("n3", n3, "")
+	writeThemeFiles("n4", n4, "")
+	writeThemeFiles("o1", o1c, o1t)
+
+	b.WithConfigFile("toml", `
+[module]
+[[module.imports]]
+path="n1"
+[[module.imports]]
+path="n4"
+
+`)
+
+	b.Build(BuildCfg{})