tpl/collections: Add collections.SymDiff

Fixes #5410

5 files changed, 204 insertions, 18 deletions

diff --git a/tpl/collections/complement.go b/tpl/collections/complement.go
index d975fabac..a5633f8b4 100644
--- a/tpl/collections/complement.go
+++ b/tpl/collections/complement.go
@@ -33,23 +33,9 @@ func (ns *Namespace) Complement(seqs ...interface{}) (interface{}, error) {
 	universe := seqs[len(seqs)-1]
 	as := seqs[:len(seqs)-1]
 
-	aset := make(map[interface{}]struct{})
-
-	for _, av := range as {
-		v := reflect.ValueOf(av)
-		switch v.Kind() {
-		case reflect.Array, reflect.Slice:
-			for i := 0; i < v.Len(); i++ {
-				ev, _ := indirectInterface(v.Index(i))
-				if !ev.Type().Comparable() {
-					return nil, errors.New("elements in complement must be comparable")
-				}
-
-				aset[normalize(ev)] = struct{}{}
-			}
-		default:
-			return nil, fmt.Errorf("arguments to complement must be slices or arrays")
-		}
+	aset, err := collectIdentities(as...)
+	if err != nil {
+		return nil, err
 	}
 
 	v := reflect.ValueOf(universe)
diff --git a/tpl/collections/init.go b/tpl/collections/init.go
index 569932c08..8dbef75c9 100644
--- a/tpl/collections/init.go
+++ b/tpl/collections/init.go
@@ -46,6 +46,13 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.SymDiff,
+			[]string{"symdiff"},
+			[][2]string{
+				{`{{ slice 1 2 3 | symdiff (slice 3 4) }}`, `[1 2 4]`},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.Delimit,
 			[]string{"delimit"},
 			[][2]string{
diff --git a/tpl/collections/reflect_helpers.go b/tpl/collections/reflect_helpers.go
index 074396479..85aa389ce 100644
--- a/tpl/collections/reflect_helpers.go
+++ b/tpl/collections/reflect_helpers.go
@@ -14,10 +14,11 @@
 package collections
 
 import (
-	"errors"
 	"fmt"
 	"reflect"
 	"time"
+
+	"github.com/pkg/errors"
 )
 
 var (
@@ -59,6 +60,47 @@ func normalize(v reflect.Value) interface{} {
 	return v.Interface()
 }
 
+// collects identities from the slices in seqs into a set. Numeric values are normalized,
+// pointers unwrapped.
+func collectIdentities(seqs ...interface{}) (map[interface{}]bool, error) {
+	seen := make(map[interface{}]bool)
+	for _, seq := range seqs {
+		v := reflect.ValueOf(seq)
+		switch v.Kind() {
+		case reflect.Array, reflect.Slice:
+			for i := 0; i < v.Len(); i++ {
+				ev, _ := indirectInterface(v.Index(i))
+				if !ev.Type().Comparable() {
+					return nil, errors.New("elements must be comparable")
+				}
+
+				seen[normalize(ev)] = true
+			}
+		default:
+			return nil, fmt.Errorf("arguments must be slices or arrays")
+		}
+	}
+
+	return seen, nil
+}
+
+// We have some different numeric and string types that we try to behave like
+// they were the same.
+func convertValue(v reflect.Value, to reflect.Type) (reflect.Value, error) {
+	if v.Type().AssignableTo(to) {
+		return v, nil
+	}
+	switch kind := to.Kind(); {
+	case kind == reflect.String:
+		s, err := toString(v)
+		return reflect.ValueOf(s), err
+	case isNumber(kind):
+		return convertNumber(v, kind)
+	default:
+		return reflect.Value{}, errors.Errorf("%s is not assignable to %s", v.Type(), to)
+	}
+}
+
 // There are potential overflows in this function, but the downconversion of
 // int64 etc. into int8 etc. is coming from the synthetic unit tests for Union etc.
 // TODO(bep) We should consider normalizing the slices to int64 etc.
diff --git a/tpl/collections/symdiff.go b/tpl/collections/symdiff.go
new file mode 100644
index 000000000..1c58257e4
--- /dev/null
+++ b/tpl/collections/symdiff.go
@@ -0,0 +1,71 @@
+// 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 collections
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/pkg/errors"
+)
+
+// SymDiff returns the symmetric difference of s1 and s2.
+// Arguments must be either a slice or an array of comparable types.
+func (ns *Namespace) SymDiff(s2, s1 interface{}) (interface{}, error) {
+	ids1, err := collectIdentities(s1)
+	if err != nil {
+		return nil, err
+	}
+	ids2, err := collectIdentities(s2)
+	if err != nil {
+		return nil, err
+	}
+
+	var slice reflect.Value
+	var sliceElemType reflect.Type
+
+	for i, s := range []interface{}{s1, s2} {
+		v := reflect.ValueOf(s)
+
+		switch v.Kind() {
+		case reflect.Array, reflect.Slice:
+			if i == 0 {
+				sliceType := v.Type()
+				sliceElemType = sliceType.Elem()
+				slice = reflect.MakeSlice(sliceType, 0, 0)
+			}
+
+			for i := 0; i < v.Len(); i++ {
+				ev, _ := indirectInterface(v.Index(i))
+				if !ev.Type().Comparable() {
+					return nil, errors.New("symdiff: elements must be comparable")
+				}
+				key := normalize(ev)
+				// Append if the key is not in their intersection.
+				if ids1[key] != ids2[key] {
+					v, err := convertValue(ev, sliceElemType)
+					if err != nil {
+						return nil, errors.WithMessage(err, "symdiff: failed to convert value")
+					}
+					slice = reflect.Append(slice, v)
+				}
+			}
+		default:
+			return nil, fmt.Errorf("arguments to symdiff must be slices or arrays")
+		}
+	}
+
+	return slice.Interface(), nil
+
+}
diff --git a/tpl/collections/symdiff_test.go b/tpl/collections/symdiff_test.go
new file mode 100644
index 000000000..d44999730
--- /dev/null
+++ b/tpl/collections/symdiff_test.go
@@ -0,0 +1,80 @@
+// 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 collections
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"github.com/gohugoio/hugo/deps"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSymDiff(t *testing.T) {
+	t.Parallel()
+
+	assert := require.New(t)
+
+	ns := New(&deps.Deps{})
+
+	s1 := []TstX{TstX{A: "a"}, TstX{A: "b"}}
+	s2 := []TstX{TstX{A: "a"}, TstX{A: "e"}}
+
+	xa, xd := &TstX{A: "a"}, &TstX{A: "d"}
+
+	sp1 := []*TstX{xa, &TstX{A: "b"}, xd, &TstX{A: "e"}}
+	sp2 := []*TstX{&TstX{A: "b"}, &TstX{A: "e"}}
+
+	for i, test := range []struct {
+		s1       interface{}
+		s2       interface{}
+		expected interface{}
+	}{
+		{[]string{"a", "x", "b", "c"}, []string{"a", "b", "y", "c"}, []string{"x", "y"}},
+		{[]string{"a", "b", "c"}, []string{"a", "b", "c"}, []string{}},
+		{[]interface{}{"a", "b", nil}, []interface{}{"a"}, []interface{}{"b", nil}},
+		{[]int{1, 2, 3}, []int{3, 4}, []int{1, 2, 4}},
+		{[]int{1, 2, 3}, []int64{3, 4}, []int{1, 2, 4}},
+		{s1, s2, []TstX{TstX{A: "b"}, TstX{A: "e"}}},
+		{sp1, sp2, []*TstX{xa, xd}},
+
+		// Errors
+		{"error", "error", false},
+		{[]int{1, 2, 3}, []string{"3", "4"}, false},
+	} {
+
+		errMsg := fmt.Sprintf("[%d]", i)
+
+		result, err := ns.SymDiff(test.s2, test.s1)
+
+		if b, ok := test.expected.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+
+		if !reflect.DeepEqual(test.expected, result) {
+			t.Fatalf("%s got\n%T: %v\nexpected\n%T: %v", errMsg, result, result, test.expected, test.expected)
+		}
+	}
+
+	_, err := ns.Complement()
+	assert.Error(err)
+	_, err = ns.Complement([]string{"a", "b"})
+	assert.Error(err)
+
+}