common/maps: Improve append in Scratch

This commit consolidates the reflective collections handling in `.Scratch` vs the `tpl` package so they use the same code paths.

This commit also adds support for a corner case where a typed slice is appended to a nil or empty `[]interface{}`.

Fixes #5275

common/collections/append.go

@@ -0,0 +1,83 @@
+// 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"
+)
+
+// Append appends from to a slice to and returns the resulting slice.
+// If lenght of from is one and the only element is a slice of same type as to,
+// it will be appended.
+func Append(to interface{}, from ...interface{}) (interface{}, error) {
+	tov, toIsNil := indirect(reflect.ValueOf(to))
+
+	toIsNil = toIsNil || to == nil
+	var tot reflect.Type
+
+	if !toIsNil {
+		if tov.Kind() != reflect.Slice {
+			return nil, fmt.Errorf("expected a slice, got %T", to)
+		}
+
+		tot = tov.Type().Elem()
+		toIsNil = tov.Len() == 0
+
+		if len(from) == 1 {
+			fromv := reflect.ValueOf(from[0])
+			if fromv.Kind() == reflect.Slice {
+				if toIsNil {
+					// If we get nil []string, we just return the []string
+					return from[0], nil
+				}
+
+				fromt := reflect.TypeOf(from[0]).Elem()
+
+				// If we get []string []string, we append the from slice to to
+				if tot == fromt {
+					return reflect.AppendSlice(tov, fromv).Interface(), nil
+				}
+			}
+		}
+	}
+
+	if toIsNil {
+		return Slice(from...), nil
+	}
+
+	for _, f := range from {
+		fv := reflect.ValueOf(f)
+		if tot != fv.Type() {
+			return nil, fmt.Errorf("append element type mismatch: expected %v, got %v", tot, fv.Type())
+		}
+		tov = reflect.Append(tov, fv)
+	}
+
+	return tov.Interface(), nil
+}
+
+// indirect is borrowed from the Go stdlib: 'text/template/exec.go'
+// TODO(bep) consolidate
+func indirect(v reflect.Value) (rv reflect.Value, isNil bool) {
+	for ; v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface; v = v.Elem() {
+		if v.IsNil() {
+			return v, true
+		}
+		if v.Kind() == reflect.Interface && v.NumMethod() > 0 {
+			break
+		}
+	}
+	return v, false
+}

common/collections/append_test.go

@@ -0,0 +1,70 @@
+// 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/stretchr/testify/require"
+)
+
+func TestAppend(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		start    interface{}
+		addend   []interface{}
+		expected interface{}
+	}{
+		{[]string{"a", "b"}, []interface{}{"c"}, []string{"a", "b", "c"}},
+		{[]string{"a", "b"}, []interface{}{"c", "d", "e"}, []string{"a", "b", "c", "d", "e"}},
+		{[]string{"a", "b"}, []interface{}{[]string{"c", "d", "e"}}, []string{"a", "b", "c", "d", "e"}},
+		{nil, []interface{}{"a", "b"}, []string{"a", "b"}},
+		{nil, []interface{}{nil}, []interface{}{nil}},
+		{[]interface{}{}, []interface{}{[]string{"c", "d", "e"}}, []string{"c", "d", "e"}},
+		{tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}},
+			[]interface{}{&tstSlicer{"c"}},
+			tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}, &tstSlicer{"c"}}},
+		{&tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}},
+			[]interface{}{&tstSlicer{"c"}},
+			tstSlicers{&tstSlicer{"a"},
+				&tstSlicer{"b"},
+				&tstSlicer{"c"}}},
+		// Errors
+		{"", []interface{}{[]string{"a", "b"}}, false},
+		// No string concatenation.
+		{"ab",
+			[]interface{}{"c"},
+			false},
+	} {
+
+		errMsg := fmt.Sprintf("[%d]", i)
+
+		result, err := Append(test.start, test.addend...)
+
+		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)
+		}
+	}
+
+}

common/collections/collections.go

@@ -19,10 +19,3 @@ package collections
 type Grouper interface {
 	Group(key interface{}, items interface{}) (interface{}, error)
 }
-
-// Slicer definse a very generic way to create a typed slice. This is used
-// in collections.Slice template func to get types such as Pages, PageGroups etc.
-// instead of the less useful []interface{}.
-type Slicer interface {
-	Slice(items interface{}) (interface{}, error)
-}

common/collections/slice.go

@@ -0,0 +1,66 @@
+// 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 (
+	"reflect"
+)
+
+// Slicer definse a very generic way to create a typed slice. This is used
+// in collections.Slice template func to get types such as Pages, PageGroups etc.
+// instead of the less useful []interface{}.
+type Slicer interface {
+	Slice(items interface{}) (interface{}, error)
+}
+
+// Slice returns a slice of all passed arguments.
+func Slice(args ...interface{}) interface{} {
+	if len(args) == 0 {
+		return args
+	}
+
+	first := args[0]
+	firstType := reflect.TypeOf(first)
+
+	if firstType == nil {
+		return args
+	}
+
+	if g, ok := first.(Slicer); ok {
+		v, err := g.Slice(args)
+		if err == nil {
+			return v
+		}
+
+		// If Slice fails, the items are not of the same type and
+		// []interface{} is the best we can do.
+		return args
+	}
+
+	if len(args) > 1 {
+		// This can be a mix of types.
+		for i := 1; i < len(args); i++ {
+			if firstType != reflect.TypeOf(args[i]) {
+				// []interface{} is the best we can do
+				return args
+			}
+		}
+	}
+
+	slice := reflect.MakeSlice(reflect.SliceOf(firstType), len(args), len(args))
+	for i, arg := range args {
+		slice.Index(i).Set(reflect.ValueOf(arg))
+	}
+	return slice.Interface()
+}

common/collections/slice_test.go

@@ -0,0 +1,125 @@
+// 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 (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/alecthomas/assert"
+)
+
+var _ Slicer = (*tstSlicer)(nil)
+var _ Slicer = (*tstSlicerIn1)(nil)
+var _ Slicer = (*tstSlicerIn2)(nil)
+var _ testSlicerInterface = (*tstSlicerIn1)(nil)
+var _ testSlicerInterface = (*tstSlicerIn1)(nil)
+
+type testSlicerInterface interface {
+	Name() string
+}
+
+type testSlicerInterfaces []testSlicerInterface
+
+type tstSlicerIn1 struct {
+	name string
+}
+
+type tstSlicerIn2 struct {
+	name string
+}
+
+type tstSlicer struct {
+	name string
+}
+
+func (p *tstSlicerIn1) Slice(in interface{}) (interface{}, error) {
+	items := in.([]interface{})
+	result := make(testSlicerInterfaces, len(items))
+	for i, v := range items {
+		switch vv := v.(type) {
+		case testSlicerInterface:
+			result[i] = vv
+		default:
+			return nil, errors.New("invalid type")
+		}
+
+	}
+	return result, nil
+}
+
+func (p *tstSlicerIn2) Slice(in interface{}) (interface{}, error) {
+	items := in.([]interface{})
+	result := make(testSlicerInterfaces, len(items))
+	for i, v := range items {
+		switch vv := v.(type) {
+		case testSlicerInterface:
+			result[i] = vv
+		default:
+			return nil, errors.New("invalid type")
+		}
+	}
+	return result, nil
+}
+
+func (p *tstSlicerIn1) Name() string {
+	return p.Name()
+}
+
+func (p *tstSlicerIn2) Name() string {
+	return p.Name()
+}
+
+func (p *tstSlicer) Slice(in interface{}) (interface{}, error) {
+	items := in.([]interface{})
+	result := make(tstSlicers, len(items))
+	for i, v := range items {
+		switch vv := v.(type) {
+		case *tstSlicer:
+			result[i] = vv
+		default:
+			return nil, errors.New("invalid type")
+		}
+	}
+	return result, nil
+}
+
+type tstSlicers []*tstSlicer
+
+func TestSlice(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		args     []interface{}
+		expected interface{}
+	}{
+		{[]interface{}{"a", "b"}, []string{"a", "b"}},
+		{[]interface{}{&tstSlicer{"a"}, &tstSlicer{"b"}}, tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}}},
+		{[]interface{}{&tstSlicer{"a"}, "b"}, []interface{}{&tstSlicer{"a"}, "b"}},
+		{[]interface{}{}, []interface{}{}},
+		{[]interface{}{nil}, []interface{}{nil}},
+		{[]interface{}{5, "b"}, []interface{}{5, "b"}},
+		{[]interface{}{&tstSlicerIn1{"a"}, &tstSlicerIn2{"b"}}, testSlicerInterfaces{&tstSlicerIn1{"a"}, &tstSlicerIn2{"b"}}},
+		{[]interface{}{&tstSlicerIn1{"a"}, &tstSlicer{"b"}}, []interface{}{&tstSlicerIn1{"a"}, &tstSlicer{"b"}}},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test.args)
+
+		result := Slice(test.args...)
+
+		assert.Equal(t, test.expected, result, errMsg)
+	}
+
+	assert.Len(t, Slice(), 0)
+}

common/maps/scratch.go

@@ -18,6 +18,7 @@ import (
 	"sort"
 	"sync"
 
+	"github.com/gohugoio/hugo/common/collections"
 	"github.com/gohugoio/hugo/common/math"
 )
 
@@ -40,14 +41,12 @@ func (c *Scratch) Add(key string, newAddend interface{}) (string, error) {
 	if found {
 		var err error
 
-		addendV := reflect.ValueOf(existingAddend)
+		addendV := reflect.TypeOf(existingAddend)
 
 		if addendV.Kind() == reflect.Slice || addendV.Kind() == reflect.Array {
-			nav := reflect.ValueOf(newAddend)
-			if nav.Kind() == reflect.Slice || nav.Kind() == reflect.Array {
-				newVal = reflect.AppendSlice(addendV, nav).Interface()
-			} else {
-				newVal = reflect.Append(addendV, nav).Interface()
+			newVal, err = collections.Append(existingAddend, newAddend)
+			if err != nil {
+				return "", err
 			}
 		} else {
 			newVal, err = math.DoArithmetic(existingAddend, newAddend, '+')

common/maps/scratch_test.go

@@ -18,29 +18,31 @@ import (
 	"sync"
 	"testing"
 
-	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestScratchAdd(t *testing.T) {
 	t.Parallel()
+	assert := require.New(t)
+
 	scratch := NewScratch()
 	scratch.Add("int1", 10)
 	scratch.Add("int1", 20)
 	scratch.Add("int2", 20)
 
-	assert.Equal(t, int64(30), scratch.Get("int1"))
-	assert.Equal(t, 20, scratch.Get("int2"))
+	assert.Equal(int64(30), scratch.Get("int1"))
+	assert.Equal(20, scratch.Get("int2"))
 
 	scratch.Add("float1", float64(10.5))
 	scratch.Add("float1", float64(20.1))
 
-	assert.Equal(t, float64(30.6), scratch.Get("float1"))
+	assert.Equal(float64(30.6), scratch.Get("float1"))
 
 	scratch.Add("string1", "Hello ")
 	scratch.Add("string1", "big ")
 	scratch.Add("string1", "World!")
 
-	assert.Equal(t, "Hello big World!", scratch.Get("string1"))
+	assert.Equal("Hello big World!", scratch.Get("string1"))
 
 	scratch.Add("scratch", scratch)
 	_, err := scratch.Add("scratch", scratch)
@@ -53,12 +55,14 @@ func TestScratchAdd(t *testing.T) {
 
 func TestScratchAddSlice(t *testing.T) {
 	t.Parallel()
+	assert := require.New(t)
+
 	scratch := NewScratch()
 
 	_, err := scratch.Add("intSlice", []int{1, 2})
-	assert.Nil(t, err)
+	assert.NoError(err)
 	_, err = scratch.Add("intSlice", 3)
-	assert.Nil(t, err)
+	assert.NoError(err)
 
 	sl := scratch.Get("intSlice")
 	expected := []int{1, 2, 3}
@@ -66,10 +70,9 @@ func TestScratchAddSlice(t *testing.T) {
 	if !reflect.DeepEqual(expected, sl) {
 		t.Errorf("Slice difference, go %q expected %q", sl, expected)
 	}
-
 	_, err = scratch.Add("intSlice", []int{4, 5})
 
-	assert.Nil(t, err)
+	assert.NoError(err)
 
 	sl = scratch.Get("intSlice")
 	expected = []int{1, 2, 3, 4, 5}
@@ -77,29 +80,47 @@ func TestScratchAddSlice(t *testing.T) {
 	if !reflect.DeepEqual(expected, sl) {
 		t.Errorf("Slice difference, go %q expected %q", sl, expected)
 	}
+}
+
+// https://github.com/gohugoio/hugo/issues/5275
+func TestScratchAddTypedSliceToInterfaceSlice(t *testing.T) {
+	t.Parallel()
+	assert := require.New(t)
+
+	scratch := NewScratch()
+	scratch.Set("slice", []interface{}{})
+
+	_, err := scratch.Add("slice", []int{1, 2})
+	assert.NoError(err)
+	assert.Equal([]int{1, 2}, scratch.Get("slice"))
 
 }
 
 func TestScratchSet(t *testing.T) {
 	t.Parallel()
+	assert := require.New(t)
+
 	scratch := NewScratch()
 	scratch.Set("key", "val")
-	assert.Equal(t, "val", scratch.Get("key"))
+	assert.Equal("val", scratch.Get("key"))
 }
 
 func TestScratchDelete(t *testing.T) {
 	t.Parallel()
+	assert := require.New(t)
+
 	scratch := NewScratch()
 	scratch.Set("key", "val")
 	scratch.Delete("key")
 	scratch.Add("key", "Lucy Parsons")
-	assert.Equal(t, "Lucy Parsons", scratch.Get("key"))
+	assert.Equal("Lucy Parsons", scratch.Get("key"))
 }
 
 // Issue #2005
 func TestScratchInParallel(t *testing.T) {
 	var wg sync.WaitGroup
 	scratch := NewScratch()
+
 	key := "counter"
 	scratch.Set(key, int64(1))
 	for i := 1; i <= 10; i++ {
@@ -142,13 +163,15 @@ func TestScratchGet(t *testing.T) {
 
 func TestScratchSetInMap(t *testing.T) {
 	t.Parallel()
+	assert := require.New(t)
+
 	scratch := NewScratch()
 	scratch.SetInMap("key", "lux", "Lux")
 	scratch.SetInMap("key", "abc", "Abc")
 	scratch.SetInMap("key", "zyx", "Zyx")
 	scratch.SetInMap("key", "abc", "Abc (updated)")
 	scratch.SetInMap("key", "def", "Def")
-	assert.Equal(t, []interface{}{0: "Abc (updated)", 1: "Def", 2: "Lux", 3: "Zyx"}, scratch.GetSortedMapValues("key"))
+	assert.Equal([]interface{}{0: "Abc (updated)", 1: "Def", 2: "Lux", 3: "Zyx"}, scratch.GetSortedMapValues("key"))
 }
 
 func TestScratchGetSortedMapValues(t *testing.T) {

tpl/collections/append.go

@@ -15,8 +15,8 @@ package collections
 
 import (
 	"errors"
-	"fmt"
-	"reflect"
+
+	"github.com/gohugoio/hugo/common/collections"
 )
 
 // Append appends the arguments up to the last one to the slice in the last argument.
@@ -33,42 +33,6 @@ func (ns *Namespace) Append(args ...interface{}) (interface{}, error) {
 	to := args[len(args)-1]
 	from := args[:len(args)-1]
 
-	tov, toIsNil := indirect(reflect.ValueOf(to))
+	return collections.Append(to, from...)
 
-	toIsNil = toIsNil || to == nil
-	var tot reflect.Type
-
-	if !toIsNil {
-		if tov.Kind() != reflect.Slice {
-			return nil, fmt.Errorf("expected a slice, got %T", to)
-		}
-
-		tot = tov.Type().Elem()
-		toIsNil = tov.Len() == 0
-
-		if len(from) == 1 {
-			// If we get []string []string, we append the from slice to to
-			fromv := reflect.ValueOf(from[0])
-			if fromv.Kind() == reflect.Slice {
-				fromt := reflect.TypeOf(from[0]).Elem()
-				if tot == fromt {
-					return reflect.AppendSlice(tov, fromv).Interface(), nil
-				}
-			}
-		}
-	}
-
-	if toIsNil {
-		return ns.Slice(from...), nil
-	}
-
-	for _, f := range from {
-		fv := reflect.ValueOf(f)
-		if tot != fv.Type() {
-			return nil, fmt.Errorf("append element type mismatch: expected %v, got %v", tot, fv.Type())
-		}
-		tov = reflect.Append(tov, fv)
-	}
-
-	return tov.Interface(), nil
 }

tpl/collections/append_test.go

@@ -18,11 +18,11 @@ import (
 	"reflect"
 	"testing"
 
-	"github.com/alecthomas/assert"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/stretchr/testify/require"
 )
 
+// Also see tests in common/collection.
 func TestAppend(t *testing.T) {
 	t.Parallel()
 
@@ -36,16 +36,6 @@ func TestAppend(t *testing.T) {
 		{[]string{"a", "b"}, []interface{}{"c"}, []string{"a", "b", "c"}},
 		{[]string{"a", "b"}, []interface{}{"c", "d", "e"}, []string{"a", "b", "c", "d", "e"}},
 		{[]string{"a", "b"}, []interface{}{[]string{"c", "d", "e"}}, []string{"a", "b", "c", "d", "e"}},
-		{nil, []interface{}{"a", "b"}, []string{"a", "b"}},
-		{nil, []interface{}{nil}, []interface{}{nil}},
-		{tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}},
-			[]interface{}{&tstSlicer{"c"}},
-			tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}, &tstSlicer{"c"}}},
-		{&tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}},
-			[]interface{}{&tstSlicer{"c"}},
-			tstSlicers{&tstSlicer{"a"},
-				&tstSlicer{"b"},
-				&tstSlicer{"c"}}},
 		// Errors
 		{"", []interface{}{[]string{"a", "b"}}, false},
 		{[]string{"a", "b"}, []interface{}{}, false},
@@ -73,5 +63,4 @@ func TestAppend(t *testing.T) {
 		}
 	}
 
-	assert.Len(t, ns.Slice(), 0)
 }

tpl/collections/apply.go

@@ -136,7 +136,7 @@ func (ns *Namespace) lookupFunc(fname string) (reflect.Value, bool) {
 	return m, true
 }
 
-// indirect is taken from 'text/template/exec.go'
+// indirect is borrowed from the Go stdlib: 'text/template/exec.go'
 func indirect(v reflect.Value) (rv reflect.Value, isNil bool) {
 	for ; v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface; v = v.Elem() {
 		if v.IsNil() {

tpl/collections/collections.go

@@ -523,39 +523,7 @@ func (ns *Namespace) Slice(args ...interface{}) interface{} {
 		return args
 	}
 
-	first := args[0]
-	firstType := reflect.TypeOf(first)
-
-	if firstType == nil {
-		return args
-	}
-
-	if g, ok := first.(collections.Slicer); ok {
-		v, err := g.Slice(args)
-		if err == nil {
-			return v
-		}
-
-		// If Slice fails, the items are not of the same type and
-		// []interface{} is the best we can do.
-		return args
-	}
-
-	if len(args) > 1 {
-		// This can be a mix of types.
-		for i := 1; i < len(args); i++ {
-			if firstType != reflect.TypeOf(args[i]) {
-				// []interface{} is the best we can do
-				return args
-			}
-		}
-	}
-
-	slice := reflect.MakeSlice(reflect.SliceOf(firstType), len(args), len(args))
-	for i, arg := range args {
-		slice.Index(i).Set(reflect.ValueOf(arg))
-	}
-	return slice.Interface()
+	return collections.Slice(args...)
 }
 
 type intersector struct {

tpl/collections/collections_test.go

@@ -25,7 +25,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/gohugoio/hugo/common/collections"
 	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/helpers"
@@ -644,83 +643,7 @@ func TestShuffleRandomising(t *testing.T) {
 	}
 }
 
-var _ collections.Slicer = (*tstSlicer)(nil)
-var _ collections.Slicer = (*tstSlicerIn1)(nil)
-var _ collections.Slicer = (*tstSlicerIn2)(nil)
-var _ testSlicerInterface = (*tstSlicerIn1)(nil)
-var _ testSlicerInterface = (*tstSlicerIn1)(nil)
-
-type testSlicerInterface interface {
-	Name() string
-}
-
-type testSlicerInterfaces []testSlicerInterface
-
-type tstSlicerIn1 struct {
-	name string
-}
-
-type tstSlicerIn2 struct {
-	name string
-}
-
-type tstSlicer struct {
-	name string
-}
-
-func (p *tstSlicerIn1) Slice(in interface{}) (interface{}, error) {
-	items := in.([]interface{})
-	result := make(testSlicerInterfaces, len(items))
-	for i, v := range items {
-		switch vv := v.(type) {
-		case testSlicerInterface:
-			result[i] = vv
-		default:
-			return nil, errors.New("invalid type")
-		}
-
-	}
-	return result, nil
-}
-
-func (p *tstSlicerIn2) Slice(in interface{}) (interface{}, error) {
-	items := in.([]interface{})
-	result := make(testSlicerInterfaces, len(items))
-	for i, v := range items {
-		switch vv := v.(type) {
-		case testSlicerInterface:
-			result[i] = vv
-		default:
-			return nil, errors.New("invalid type")
-		}
-	}
-	return result, nil
-}
-
-func (p *tstSlicerIn1) Name() string {
-	return p.Name()
-}
-
-func (p *tstSlicerIn2) Name() string {
-	return p.Name()
-}
-
-func (p *tstSlicer) Slice(in interface{}) (interface{}, error) {
-	items := in.([]interface{})
-	result := make(tstSlicers, len(items))
-	for i, v := range items {
-		switch vv := v.(type) {
-		case *tstSlicer:
-			result[i] = vv
-		default:
-			return nil, errors.New("invalid type")
-		}
-	}
-	return result, nil
-}
-
-type tstSlicers []*tstSlicer
-
+// Also see tests in commons/collection.
 func TestSlice(t *testing.T) {
 	t.Parallel()
 
@@ -731,14 +654,10 @@ func TestSlice(t *testing.T) {
 		expected interface{}
 	}{
 		{[]interface{}{"a", "b"}, []string{"a", "b"}},
-		{[]interface{}{&tstSlicer{"a"}, &tstSlicer{"b"}}, tstSlicers{&tstSlicer{"a"}, &tstSlicer{"b"}}},
-		{[]interface{}{&tstSlicer{"a"}, "b"}, []interface{}{&tstSlicer{"a"}, "b"}},
 		{[]interface{}{}, []interface{}{}},
 		{[]interface{}{nil}, []interface{}{nil}},
 		{[]interface{}{5, "b"}, []interface{}{5, "b"}},
 		{[]interface{}{tstNoStringer{}}, []tstNoStringer{tstNoStringer{}}},
-		{[]interface{}{&tstSlicerIn1{"a"}, &tstSlicerIn2{"b"}}, testSlicerInterfaces{&tstSlicerIn1{"a"}, &tstSlicerIn2{"b"}}},
-		{[]interface{}{&tstSlicerIn1{"a"}, &tstSlicer{"b"}}, []interface{}{&tstSlicerIn1{"a"}, &tstSlicer{"b"}}},
 	} {
 		errMsg := fmt.Sprintf("[%d] %v", i, test.args)