tpl/collections: Add Merge function

Merges two maps recursively and returns a new one. Merge is case-insensitive.

Fixes #5992

3 files changed, 281 insertions, 0 deletions

diff --git a/tpl/collections/init.go b/tpl/collections/init.go
index 8dbef75c9..17ca16543 100644
--- a/tpl/collections/init.go
+++ b/tpl/collections/init.go
@@ -183,6 +183,16 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.Merge,
+			[]string{"merge"},
+			[][2]string{
+				{`{{ dict "title" "Hugo Rocks!" | collections.Merge (dict "title" "Default Title" "description" "Yes, Hugo Rocks!") | sort }}`,
+					`[Yes, Hugo Rocks! Hugo Rocks!]`},
+				{`{{  merge (dict "title" "Default Title" "description" "Yes, Hugo Rocks!") (dict "title" "Hugo Rocks!") | sort }}`,
+					`[Yes, Hugo Rocks! Hugo Rocks!]`},
+			},
+		)
+
 		return ns
 
 	}
diff --git a/tpl/collections/merge.go b/tpl/collections/merge.go
new file mode 100644
index 000000000..6916d0710
--- /dev/null
+++ b/tpl/collections/merge.go
@@ -0,0 +1,98 @@
+// Copyright 2019 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 collections
+
+import (
+	"reflect"
+	"strings"
+
+	"github.com/gohugoio/hugo/common/hreflect"
+
+	"github.com/pkg/errors"
+)
+
+// Merge creates a copy of dst and merges src into it.
+// Currently only maps supported. Key handling is case insensitive.
+func (ns *Namespace) Merge(src, dst interface{}) (interface{}, error) {
+
+	vdst, vsrc := reflect.ValueOf(dst), reflect.ValueOf(src)
+
+	if vdst.Kind() != reflect.Map {
+		return nil, errors.Errorf("destination must be a map, got %T", dst)
+	}
+
+	if !hreflect.IsTruthfulValue(vsrc) {
+		return dst, nil
+	}
+
+	if vsrc.Kind() != reflect.Map {
+		return nil, errors.Errorf("source must be a map, got %T", src)
+	}
+
+	if vsrc.Type() != vdst.Type() {
+		return nil, errors.Errorf("incompatible map types, got %T to %T", src, dst)
+	}
+
+	return mergeMap(vdst, vsrc).Interface(), nil
+}
+
+func caseInsensitiveLookup(m, k reflect.Value) (reflect.Value, bool) {
+	if m.Type().Key().Kind() != reflect.String || k.Kind() != reflect.String {
+		// Fall back to direct lookup.
+		v := m.MapIndex(k)
+		return v, hreflect.IsTruthfulValue(v)
+	}
+
+	for _, key := range m.MapKeys() {
+		if strings.EqualFold(k.String(), key.String()) {
+			return m.MapIndex(key), true
+		}
+
+	}
+
+	return reflect.Value{}, false
+}
+
+func mergeMap(dst, src reflect.Value) reflect.Value {
+
+	out := reflect.MakeMap(dst.Type())
+
+	// Copy the destination map.
+	for _, key := range dst.MapKeys() {
+		v := dst.MapIndex(key)
+		out.SetMapIndex(key, v)
+	}
+
+	// Add all keys in src not already in destination.
+	// Maps of the same type will be merged.
+	for _, key := range src.MapKeys() {
+		sv := src.MapIndex(key)
+		dv, found := caseInsensitiveLookup(dst, key)
+
+		if found {
+			// If both are the same map type, merge.
+			dve := dv.Elem()
+			if dve.Kind() == reflect.Map {
+				sve := sv.Elem()
+				if dve.Type() == sve.Type() {
+					out.SetMapIndex(key, mergeMap(dve, sve))
+				}
+			}
+		} else {
+			out.SetMapIndex(key, sv)
+		}
+	}
+
+	return out
+}
diff --git a/tpl/collections/merge_test.go b/tpl/collections/merge_test.go
new file mode 100644
index 000000000..9e34a6e98
--- /dev/null
+++ b/tpl/collections/merge_test.go
@@ -0,0 +1,173 @@
+// Copyright 2019 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 collections
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/gohugoio/hugo/parser"
+
+	"github.com/gohugoio/hugo/parser/metadecoders"
+
+	"github.com/gohugoio/hugo/deps"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMerge(t *testing.T) {
+
+	ns := New(&deps.Deps{})
+
+	simpleMap := map[string]interface{}{"a": 1, "b": 2}
+
+	for i, test := range []struct {
+		name   string
+		dst    interface{}
+		src    interface{}
+		expect interface{}
+		isErr  bool
+	}{
+		{
+			"basic",
+			map[string]interface{}{"a": 1, "b": 2},
+			map[string]interface{}{"a": 42, "c": 3},
+			map[string]interface{}{"a": 1, "b": 2, "c": 3}, false},
+		{
+			"basic case insensitive",
+			map[string]interface{}{"a": 1, "b": 2},
+			map[string]interface{}{"A": 42, "c": 3},
+			map[string]interface{}{"a": 1, "b": 2, "c": 3}, false},
+		{
+			"nested",
+			map[string]interface{}{"a": 1, "b": map[string]interface{}{"d": 1, "e": 2}},
+			map[string]interface{}{"a": 42, "c": 3, "b": map[string]interface{}{"d": 55, "e": 66, "f": 3}},
+			map[string]interface{}{"a": 1, "b": map[string]interface{}{"d": 1, "e": 2, "f": 3}, "c": 3}, false},
+		{"src nil", simpleMap, nil, simpleMap, false},
+		// Error cases.
+		{"dst not a map", "not a map", nil, nil, true},
+		{"src not a map", simpleMap, "not a map", nil, true},
+		{"diferent map typs", simpleMap, map[int]interface{}{32: "a"}, nil, true},
+		{"all nil", nil, nil, nil, true},
+	} {
+
+		test := test
+
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+			assert := require.New(t)
+
+			srcStr, dstStr := fmt.Sprint(test.src), fmt.Sprint(test.dst)
+
+			result, err := ns.Merge(test.src, test.dst)
+
+			if test.isErr {
+				assert.Error(err, errMsg)
+				return
+			}
+
+			assert.NoError(err, errMsg)
+			assert.Equal(test.expect, result, errMsg)
+
+			// map sort in fmt was fixed in go 1.12.
+			if !strings.HasPrefix(runtime.Version(), "go1.11") {
+				// Verify that the original maps are preserved.
+				assert.Equal(srcStr, fmt.Sprint(test.src))
+				assert.Equal(dstStr, fmt.Sprint(test.dst))
+			}
+
+		})
+	}
+}
+
+func TestMergeDataFormats(t *testing.T) {
+	assert := require.New(t)
+	ns := New(&deps.Deps{})
+
+	toml1 := `
+V1 = "v1_1"
+
+[V2s]
+V21 = "v21_1"
+
+`
+
+	toml2 := `
+V1 = "v1_2"
+V2 = "v2_2"
+
+[V2s]
+V21 = "v21_2"
+V22 = "v22_2"
+
+`
+
+	meta1, err := metadecoders.Default.UnmarshalToMap([]byte(toml1), metadecoders.TOML)
+	assert.NoError(err)
+	meta2, err := metadecoders.Default.UnmarshalToMap([]byte(toml2), metadecoders.TOML)
+	assert.NoError(err)
+
+	for _, format := range []metadecoders.Format{metadecoders.JSON, metadecoders.YAML, metadecoders.TOML} {
+
+		var dataStr1, dataStr2 bytes.Buffer
+		err = parser.InterfaceToConfig(meta1, format, &dataStr1)
+		assert.NoError(err)
+		err = parser.InterfaceToConfig(meta2, format, &dataStr2)
+		assert.NoError(err)
+
+		dst, err := metadecoders.Default.UnmarshalToMap(dataStr1.Bytes(), format)
+		assert.NoError(err)
+		src, err := metadecoders.Default.UnmarshalToMap(dataStr2.Bytes(), format)
+		assert.NoError(err)
+
+		merged, err := ns.Merge(src, dst)
+		assert.NoError(err)
+
+		assert.Equal(map[string]interface{}{"V1": "v1_1", "V2": "v2_2", "V2s": map[string]interface{}{"V21": "v21_1", "V22": "v22_2"}}, merged)
+	}
+
+}
+
+func TestCaseInsensitiveMapLookup(t *testing.T) {
+	assert := require.New(t)
+
+	m1 := reflect.ValueOf(map[string]interface{}{
+		"a": 1,
+		"B": 2,
+	})
+
+	m2 := reflect.ValueOf(map[int]interface{}{
+		1: 1,
+		2: 2,
+	})
+
+	var found bool
+
+	a, found := caseInsensitiveLookup(m1, reflect.ValueOf("A"))
+	assert.True(found)
+	assert.Equal(1, a.Interface())
+
+	b, found := caseInsensitiveLookup(m1, reflect.ValueOf("b"))
+	assert.True(found)
+	assert.Equal(2, b.Interface())
+
+	two, found := caseInsensitiveLookup(m2, reflect.ValueOf(2))
+	assert.True(found)
+	assert.Equal(2, two.Interface())
+}