Add /config dir support

This commit adds support for a configuration directory (default `config`). The different pieces in this puzzle are:

* A new `--environment` (or `-e`) flag. This can also be set with the `HUGO_ENVIRONMENT` OS environment variable. The value for `environment` defaults to `production` when running `hugo` and `development` when running `hugo server`. You can set it to any value you want (e.g. `hugo server -e "Sensible Environment"`), but as it is used to load configuration from the file system, the letter case may be important. You can get this value in your templates with `{{ hugo.Environment }}`.
* A new `--configDir` flag (defaults to `config` below your project). This can also be set with `HUGO_CONFIGDIR` OS environment variable.

If the `configDir` exists, the configuration files will be read and merged on top of each other from left to right; the right-most value will win on duplicates.

Given the example tree below:

If `environment` is `production`, the left-most `config.toml` would be the one directly below the project (this can now be omitted if you want), and then `_default/config.toml` and finally `production/config.toml`. And since these will be merged, you can just provide the environment specific configuration setting in you production config, e.g. `enableGitInfo = true`. The order within the directories will be lexical (`config.toml` and then `params.toml`).

```bash
config
├── _default
│   ├── config.toml
│   ├── languages.toml
│   ├── menus
│   │   ├── menus.en.toml
│   │   └── menus.zh.toml
│   └── params.toml
├── development
│   └── params.toml
└── production
    ├── config.toml
    └── params.toml
```

Some configuration maps support the language code in the filename (e.g. `menus.en.toml`): `menus` (`menu` also works) and `params`.

Also note that the only folders with "a meaning" in the above listing is the top level directories below `config`. The `menus` sub folder is just added for better organization.

We use `TOML` in the example above, but Hugo also supports `JSON` and `YAML` as configuration formats. These can be mixed.

Fixes #5422

1 files changed, 10 insertions, 10 deletions

diff --git a/hugolib/testhelpers_test.go b/hugolib/testhelpers_test.go
index 33f973e96..a60ca2905 100644
--- a/hugolib/testhelpers_test.go
+++ b/hugolib/testhelpers_test.go
@@ -322,6 +322,15 @@ func (s *sitesBuilder) CreateSites() *sitesBuilder {
 	return s
 }
 
+func (s *sitesBuilder) LoadConfig() error {
+	cfg, _, err := LoadConfig(ConfigSourceDescriptor{Fs: s.Fs.Source, Filename: "config." + s.configFormat})
+	if err != nil {
+		return err
+	}
+	s.Cfg = cfg
+	return nil
+}
+
 func (s *sitesBuilder) CreateSitesE() error {
 	s.addDefaults()
 	s.writeFilePairs("content", s.contentFilePairs)
@@ -334,18 +343,9 @@ func (s *sitesBuilder) CreateSitesE() error {
 	s.writeFilePairs("i18n", s.i18nFilePairsAdded)
 
 	if s.Cfg == nil {
-		cfg, _, err := LoadConfig(ConfigSourceDescriptor{Fs: s.Fs.Source, Filename: "config." + s.configFormat})
-		if err != nil {
+		if err := s.LoadConfig(); err != nil {
 			return err
 		}
-		// TODO(bep)
-		/*		expectedConfigs := 1
-				if s.theme != "" {
-					expectedConfigs = 2
-				}
-				require.Equal(s.T, expectedConfigs, len(configFiles), fmt.Sprintf("Configs: %v", configFiles))
-		*/
-		s.Cfg = cfg
 	}
 
 	sites, err := NewHugoSites(deps.DepsCfg{Fs: s.Fs, Cfg: s.Cfg, Logger: s.logger, Running: s.running})