hugolib: Implement "related content"

This closes #98, even if this commit does not do full content text search.

We may revisit that problem in the future, but that deserves its own issue.

Fixes #98

common/types/types.go

@@ -0,0 +1,44 @@
+// Copyright 2017-present 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 types contains types shared between packages in Hugo.
+package types
+
+import (
+	"fmt"
+
+	"github.com/spf13/cast"
+)
+
+// KeyValues holds an key and a slice of values.
+type KeyValues struct {
+	Key    interface{}
+	Values []interface{}
+}
+
+// KeyString returns the key as a string, an empty string if conversion fails.
+func (k KeyValues) KeyString() string {
+	return cast.ToString(k.Key)
+}
+
+func (k KeyValues) String() string {
+	return fmt.Sprintf("%v: %v", k.Key, k.Values)
+}
+
+func NewKeyValuesStrings(key string, values ...string) KeyValues {
+	iv := make([]interface{}, len(values))
+	for i := 0; i < len(values); i++ {
+		iv[i] = values[i]
+	}
+	return KeyValues{Key: key, Values: iv}
+}

common/types/types_test.go

@@ -0,0 +1,29 @@
+// Copyright 2017-present 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 types
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestKeyValues(t *testing.T) {
+	assert := require.New(t)
+
+	kv := NewKeyValuesStrings("key", "a1", "a2")
+
+	assert.Equal("key", kv.KeyString())
+	assert.Equal([]interface{}{"a1", "a2"}, kv.Values)
+}