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

5 files changed, 7 insertions, 167 deletions

diff --git a/tpl/collections/append.go b/tpl/collections/append.go
index 20afa0e72..297328dc8 100644
--- a/tpl/collections/append.go
+++ b/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))
-
-	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 collections.Append(to, from...)
 
-	return tov.Interface(), nil
 }
diff --git a/tpl/collections/append_test.go b/tpl/collections/append_test.go
index b0a751fb8..f886aca22 100644
--- a/tpl/collections/append_test.go
+++ b/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)
 }
diff --git a/tpl/collections/apply.go b/tpl/collections/apply.go
index 0b2b00621..d715aeb00 100644
--- a/tpl/collections/apply.go
+++ b/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() {
diff --git a/tpl/collections/collections.go b/tpl/collections/collections.go
index 6d11d75f4..d9baddf6b 100644
--- a/tpl/collections/collections.go
+++ b/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 {
diff --git a/tpl/collections/collections_test.go b/tpl/collections/collections_test.go
index dc8929f39..c8a7207ea 100644
--- a/tpl/collections/collections_test.go
+++ b/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)