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

6 files changed, 175 insertions, 27 deletions

diff --git a/common/herrors/error_locator.go b/common/herrors/error_locator.go
index 88cb06c8c..3a72f4790 100644
--- a/common/herrors/error_locator.go
+++ b/common/herrors/error_locator.go
@@ -17,10 +17,10 @@ package herrors
 import (
 	"io"
 	"io/ioutil"
+	"path/filepath"
 	"strings"
 
 	"github.com/gohugoio/hugo/common/text"
-	"github.com/gohugoio/hugo/helpers"
 
 	"github.com/spf13/afero"
 )
@@ -172,12 +172,16 @@ func chromaLexerFromType(fileType string) string {
 	return fileType
 }
 
+func extNoDelimiter(filename string) string {
+	return strings.TrimPrefix(".", filepath.Ext(filename))
+}
+
 func chromaLexerFromFilename(filename string) string {
 	if strings.Contains(filename, "layouts") {
 		return "go-html-template"
 	}
 
-	ext := helpers.ExtNoDelimiter(filename)
+	ext := extNoDelimiter(filename)
 	return chromaLexerFromType(ext)
 }
 
diff --git a/common/hugo/hugo.go b/common/hugo/hugo.go
index b93b10bf1..62d923bf0 100644
--- a/common/hugo/hugo.go
+++ b/common/hugo/hugo.go
@@ -18,28 +18,50 @@ import (
 	"html/template"
 )
 
+const (
+	EnvironmentDevelopment = "development"
+	EnvironmentProduction  = "production"
+)
+
 var (
-	// CommitHash contains the current Git revision. Use make to build to make
+	// commitHash contains the current Git revision. Use make to build to make
 	// sure this gets set.
-	CommitHash string
+	commitHash string
 
-	// BuildDate contains the date of the current build.
-	BuildDate string
+	// buildDate contains the date of the current build.
+	buildDate string
 )
 
 // Info contains information about the current Hugo environment
 type Info struct {
-	Version    VersionString
-	Generator  template.HTML
 	CommitHash string
 	BuildDate  string
+
+	// The build environment.
+	// Defaults are "production" (hugo) and "development" (hugo server).
+	// This can also be set by the user.
+	// It can be any string, but it will be all lower case.
+	Environment string
 }
 
-func NewInfo() Info {
+// Version returns the current version as a comparable version string.
+func (i Info) Version() VersionString {
+	return CurrentVersion.Version()
+}
+
+// Generator a Hugo meta generator HTML tag.
+func (i Info) Generator() template.HTML {
+	return template.HTML(fmt.Sprintf(`<meta name="generator" content="Hugo %s" />`, CurrentVersion.String()))
+}
+
+// NewInfo creates a new Hugo Info object.
+func NewInfo(environment string) Info {
+	if environment == "" {
+		environment = EnvironmentProduction
+	}
 	return Info{
-		Version:    CurrentVersion.Version(),
-		CommitHash: CommitHash,
-		BuildDate:  BuildDate,
-		Generator:  template.HTML(fmt.Sprintf(`<meta name="generator" content="Hugo %s" />`, CurrentVersion.String())),
+		CommitHash:  commitHash,
+		BuildDate:   buildDate,
+		Environment: environment,
 	}
 }
diff --git a/common/hugo/hugo_test.go b/common/hugo/hugo_test.go
index 18a9b594f..1769db587 100644
--- a/common/hugo/hugo_test.go
+++ b/common/hugo/hugo_test.go
@@ -23,12 +23,13 @@ import (
 func TestHugoInfo(t *testing.T) {
 	assert := require.New(t)
 
-	hugoInfo := NewInfo()
+	hugoInfo := NewInfo("")
 
-	assert.Equal(CurrentVersion.Version(), hugoInfo.Version)
-	assert.IsType(VersionString(""), hugoInfo.Version)
-	assert.Equal(CommitHash, hugoInfo.CommitHash)
-	assert.Equal(BuildDate, hugoInfo.BuildDate)
-	assert.Contains(hugoInfo.Generator, fmt.Sprintf("Hugo %s", hugoInfo.Version))
+	assert.Equal(CurrentVersion.Version(), hugoInfo.Version())
+	assert.IsType(VersionString(""), hugoInfo.Version())
+	assert.Equal(commitHash, hugoInfo.CommitHash)
+	assert.Equal(buildDate, hugoInfo.BuildDate)
+	assert.Equal("production", hugoInfo.Environment)
+	assert.Contains(hugoInfo.Generator(), fmt.Sprintf("Hugo %s", hugoInfo.Version()))
 
 }
diff --git a/common/hugo/version.go b/common/hugo/version.go
index 204f8f747..e9deb6acf 100644
--- a/common/hugo/version.go
+++ b/common/hugo/version.go
@@ -130,8 +130,8 @@ func BuildVersionString() string {
 	program := "Hugo Static Site Generator"
 
 	version := "v" + CurrentVersion.String()
-	if CommitHash != "" {
-		version += "-" + strings.ToUpper(CommitHash)
+	if commitHash != "" {
+		version += "-" + strings.ToUpper(commitHash)
 	}
 	if isExtended {
 		version += "/extended"
@@ -139,14 +139,12 @@ func BuildVersionString() string {
 
 	osArch := runtime.GOOS + "/" + runtime.GOARCH
 
-	var buildDate string
-	if BuildDate != "" {
-		buildDate = BuildDate
-	} else {
-		buildDate = "unknown"
+	date := buildDate
+	if date == "" {
+		date = "unknown"
 	}
 
-	return fmt.Sprintf("%s %s %s BuildDate: %s", program, version, osArch, buildDate)
+	return fmt.Sprintf("%s %s %s BuildDate: %s", program, version, osArch, date)
 
 }
 
diff --git a/common/maps/maps.go b/common/maps/maps.go
index a114b557c..e0d4f964d 100644
--- a/common/maps/maps.go
+++ b/common/maps/maps.go
@@ -16,6 +16,8 @@ package maps
 import (
 	"strings"
 
+	"github.com/gobwas/glob"
+
 	"github.com/spf13/cast"
 )
 
@@ -42,3 +44,73 @@ func ToLower(m map[string]interface{}) {
 
 	}
 }
+
+type keyRename struct {
+	pattern glob.Glob
+	newKey  string
+}
+
+// KeyRenamer supports renaming of keys in a map.
+type KeyRenamer struct {
+	renames []keyRename
+}
+
+// NewKeyRenamer creates a new KeyRenamer given a list of pattern and new key
+// value pairs.
+func NewKeyRenamer(patternKeys ...string) (KeyRenamer, error) {
+	var renames []keyRename
+	for i := 0; i < len(patternKeys); i += 2 {
+		g, err := glob.Compile(strings.ToLower(patternKeys[i]), '/')
+		if err != nil {
+			return KeyRenamer{}, err
+		}
+		renames = append(renames, keyRename{pattern: g, newKey: patternKeys[i+1]})
+	}
+
+	return KeyRenamer{renames: renames}, nil
+}
+
+func (r KeyRenamer) getNewKey(keyPath string) string {
+	for _, matcher := range r.renames {
+		if matcher.pattern.Match(keyPath) {
+			return matcher.newKey
+		}
+	}
+
+	return ""
+}
+
+// Rename renames the keys in the given map according
+// to the patterns in the current KeyRenamer.
+func (r KeyRenamer) Rename(m map[string]interface{}) {
+	r.renamePath("", m)
+}
+
+func (KeyRenamer) keyPath(k1, k2 string) string {
+	k1, k2 = strings.ToLower(k1), strings.ToLower(k2)
+	if k1 == "" {
+		return k2
+	} else {
+		return k1 + "/" + k2
+	}
+}
+
+func (r KeyRenamer) renamePath(parentKeyPath string, m map[string]interface{}) {
+	for key, val := range m {
+		keyPath := r.keyPath(parentKeyPath, key)
+		switch val.(type) {
+		case map[interface{}]interface{}:
+			val = cast.ToStringMap(val)
+			r.renamePath(keyPath, val.(map[string]interface{}))
+		case map[string]interface{}:
+			r.renamePath(keyPath, val.(map[string]interface{}))
+		}
+
+		newKey := r.getNewKey(keyPath)
+
+		if newKey != "" {
+			delete(m, key)
+			m[newKey] = val
+		}
+	}
+}
diff --git a/common/maps/maps_test.go b/common/maps/maps_test.go
index 37add5dc5..29bffa6bc 100644
--- a/common/maps/maps_test.go
+++ b/common/maps/maps_test.go
@@ -16,6 +16,8 @@ package maps
 import (
 	"reflect"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestToLower(t *testing.T) {
@@ -70,3 +72,52 @@ func TestToLower(t *testing.T) {
 		}
 	}
 }
+
+func TestRenameKeys(t *testing.T) {
+	assert := require.New(t)
+
+	m := map[string]interface{}{
+		"a":    32,
+		"ren1": "m1",
+		"ren2": "m1_2",
+		"sub": map[string]interface{}{
+			"subsub": map[string]interface{}{
+				"REN1": "m2",
+				"ren2": "m2_2",
+			},
+		},
+		"no": map[string]interface{}{
+			"ren1": "m2",
+			"ren2": "m2_2",
+		},
+	}
+
+	expected := map[string]interface{}{
+		"a":    32,
+		"new1": "m1",
+		"new2": "m1_2",
+		"sub": map[string]interface{}{
+			"subsub": map[string]interface{}{
+				"new1": "m2",
+				"ren2": "m2_2",
+			},
+		},
+		"no": map[string]interface{}{
+			"ren1": "m2",
+			"ren2": "m2_2",
+		},
+	}
+
+	renamer, err := NewKeyRenamer(
+		"{ren1,sub/*/ren1}", "new1",
+		"{Ren2,sub/ren2}", "new2",
+	)
+	assert.NoError(err)
+
+	renamer.Rename(m)
+
+	if !reflect.DeepEqual(expected, m) {
+		t.Errorf("Expected\n%#v, got\n%#v\n", expected, m)
+	}
+
+}