hugolib: Integrate new page parser

See #5324

parser/metadecoders/yaml.go

@@ -0,0 +1,84 @@
+// 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.
+
+// The metadecoders package contains functions to decode metadata (e.g. page front matter)
+// from different formats: TOML, YAML, JSON.
+package metadecoders
+
+import (
+	"fmt"
+
+	"github.com/spf13/cast"
+	yaml "gopkg.in/yaml.v1"
+)
+
+// HandleYAMLData unmarshals YAML-encoded datum and returns a Go interface
+// representing the encoded data structure.
+func HandleYAMLData(datum []byte) (interface{}, error) {
+	var m interface{}
+	err := yaml.Unmarshal(datum, &m)
+	if err != nil {
+		return nil, err
+	}
+
+	// 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 mm, changed := stringifyMapKeys(m); changed {
+		return mm, nil
+	}
+
+	return m, nil
+}
+
+// stringifyMapKeys recurses into in and changes all instances of
+// map[interface{}]interface{} to map[string]interface{}. This is useful to
+// work around the impedence mismatch between JSON and YAML unmarshaling that's
+// described here: https://github.com/go-yaml/yaml/issues/139
+//
+// Inspired by https://github.com/stripe/stripe-mock, MIT licensed
+func stringifyMapKeys(in interface{}) (interface{}, bool) {
+	switch in := in.(type) {
+	case []interface{}:
+		for i, v := range in {
+			if vv, replaced := stringifyMapKeys(v); replaced {
+				in[i] = vv
+			}
+		}
+	case map[interface{}]interface{}:
+		res := make(map[string]interface{})
+		var (
+			ok  bool
+			err error
+		)
+		for k, v := range in {
+			var ks string
+
+			if ks, ok = k.(string); !ok {
+				ks, err = cast.ToStringE(k)
+				if err != nil {
+					ks = fmt.Sprintf("%v", k)
+				}
+			}
+			if vv, replaced := stringifyMapKeys(v); replaced {
+				res[ks] = vv
+			} else {
+				res[ks] = v
+			}
+		}
+		return res, true
+	}
+
+	return nil, false
+}