Allow themes to define output formats, media types and params

Fixes gohugoio#4490

Gopkg.toml

@@ -141,3 +141,7 @@
   name = "github.com/muesli/smartcrop"
   branch = "master"
 
+
+[[constraint]]
+  name = "github.com/sanity-io/litter"
+  version = "1.1.0"

hugolib/config.go

@@ -16,6 +16,7 @@ package hugolib
 import (
 	"errors"
 	"fmt"
+	"path/filepath"
 
 	"io"
 	"strings"
@@ -85,7 +86,8 @@ func LoadConfig(d ConfigSourceDescriptor) (*viper.Viper, error) {
 		return v, err
 	}
 
-	return v, nil
+	return v, loadThemeConfig(fs, v)
+
 }
 
 func loadLanguageSettings(cfg config.Provider, oldLangs helpers.Languages) error {
@@ -201,6 +203,111 @@ func loadLanguageSettings(cfg config.Provider, oldLangs helpers.Languages) error
 	return nil
 }
 
+func loadThemeConfig(fs afero.Fs, v1 *viper.Viper) error {
+
+	theme := v1.GetString("theme")
+	if theme == "" {
+		return nil
+	}
+
+	themesDir := v1.GetString("themesDir")
+	configDir := filepath.Join(themesDir, theme)
+
+	var configPath string
+	var exists bool
+	var err error
+
+	for _, exensionsToCheck := range []string{"toml", "yaml", "yml", "json"} {
+		configPath = filepath.Join(configDir, "config."+exensionsToCheck)
+		exists, err = helpers.Exists(configPath, fs)
+		if err != nil {
+			return err
+		}
+		if exists {
+			break
+		}
+	}
+
+	if !exists {
+		return nil
+	}
+
+	v2 := viper.New()
+	v2.SetFs(fs)
+	v2.AutomaticEnv()
+	v2.SetEnvPrefix("hugo")
+	v2.SetConfigFile(configPath)
+
+	err = v2.ReadInConfig()
+	if err != nil {
+		return err
+	}
+
+	for _, key := range []string{"params", "outputformats", "mediatypes"} {
+		mergeStringMapKeepLeft(key, v1, v2)
+	}
+
+	themeLower := strings.ToLower(theme)
+	themeParamsNamespace := "params." + themeLower
+	// Set namespaced params
+	if v2.IsSet("params") && !v1.IsSet(themeParamsNamespace) {
+		v1.Set(themeParamsNamespace, v2.Get("params"))
+	}
+
+	// Only add params, we do not add language definitions.
+	if v1.IsSet("languages") && v2.IsSet("languages") {
+		v1Langs := v1.GetStringMap("languages")
+		for k, _ := range v1Langs {
+			mergeStringMapKeepLeft("languages."+k+".params", v1, v2)
+		}
+		v2Langs := v2.GetStringMap("languages")
+		for k, _ := range v2Langs {
+			langParamsKey := "languages." + k + ".params"
+			langParamsThemeNamespace := langParamsKey + "." + themeLower
+			// Set namespaced params
+			if v2.IsSet(langParamsKey) && !v1.IsSet(langParamsThemeNamespace) {
+				v1.Set(langParamsThemeNamespace, v2.Get(langParamsKey))
+			}
+		}
+	}
+
+	// Add menu definitions from theme not found in project
+	if v2.IsSet("menu") {
+		v2menus := v2.GetStringMap("menu")
+		for k, v := range v2menus {
+			if !v1.IsSet("menu." + k) {
+				v1.Set("menu."+k, v)
+			}
+		}
+	}
+
+	return nil
+
+}
+
+func mergeStringMapKeepLeft(key string, v1, v2 *viper.Viper) {
+	if !v1.IsSet(key) {
+		if v2.IsSet(key) {
+			v1.Set(key, v2.Get(key))
+		}
+		return
+	}
+
+	if !v2.IsSet(key) {
+		return
+	}
+
+	m1 := v1.GetStringMap(key)
+	m2 := v2.GetStringMap(key)
+
+	for k, v := range m2 {
+		if _, found := m1[k]; !found {
+			m1[k] = v
+		}
+	}
+
+}
+
 func loadDefaultSettingsFor(v *viper.Viper) error {
 
 	c, err := helpers.NewContentSpec(v)
@@ -282,4 +389,5 @@ lastmod = ["lastmod" ,":fileModTime", ":default"]
 	}
 
 	return loadLanguageSettings(v, nil)
+
 }