hugolib: Integrate new page parser

See #5324

parser/metadecoders/decoder.go

@@ -0,0 +1,95 @@
+// Copyright 2018 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 metadecoders
+
+import (
+	"encoding/json"
+
+	"github.com/BurntSushi/toml"
+	"github.com/chaseadamsio/goorgeous"
+	"github.com/gohugoio/hugo/parser/pageparser"
+	"github.com/pkg/errors"
+	yaml "gopkg.in/yaml.v1"
+)
+
+type Format string
+
+const (
+	// These are the supported metdata  formats in Hugo. Most of these are also
+	// supported as /data formats.
+	ORG  Format = "org"
+	JSON Format = "json"
+	TOML Format = "toml"
+	YAML Format = "yaml"
+)
+
+// FormatFromFrontMatterType will return empty if not supported.
+func FormatFromFrontMatterType(typ pageparser.ItemType) Format {
+	switch typ {
+	case pageparser.TypeFrontMatterJSON:
+		return JSON
+	case pageparser.TypeFrontMatterORG:
+		return ORG
+	case pageparser.TypeFrontMatterTOML:
+		return TOML
+	case pageparser.TypeFrontMatterYAML:
+		return YAML
+	default:
+		return ""
+	}
+}
+
+// UnmarshalToMap will unmarshall data in format f into a new map. This is
+// what's needed for Hugo's front matter decoding.
+func UnmarshalToMap(data []byte, f Format) (map[string]interface{}, error) {
+	m := make(map[string]interface{})
+
+	if data == nil {
+		return m, nil
+	}
+
+	var err error
+
+	switch f {
+	case ORG:
+		m, err = goorgeous.OrgHeaders(data)
+	case JSON:
+		err = json.Unmarshal(data, &m)
+	case TOML:
+		_, err = toml.Decode(string(data), &m)
+	case YAML:
+		err = yaml.Unmarshal(data, &m)
+
+		// To support boolean keys, the `yaml` package unmarshals maps to
+		// map[interface{}]interface{}. Here we recurse through the result
+		// and change all maps to map[string]interface{} like we would've
+		// gotten from `json`.
+		if err == nil {
+			for k, v := range m {
+				if vv, changed := stringifyMapKeys(v); changed {
+					m[k] = vv
+				}
+			}
+		}
+	default:
+		return nil, errors.Errorf("unmarshal of format %q is not supported", f)
+	}
+
+	if err != nil {
+		return nil, errors.Wrapf(err, "unmarshal failed for format %q", f)
+	}
+
+	return m, nil
+
+}