Make sort tpl func accept field/key chaining arg

'sort' template function used to accept only each element's struct field
name, method name and map key name as its second argument. This extends
it to accept a field/method/key chaining key string like
'Params.foo.bar' as the argument. It evaluates sub elements of each
array or map elements and sorts by them.

Typical use case would be sorting pages by user defined front matter
value. For example, sorting pages by 'Params.foo.bar' is possible by
writing the following template code

    {{ range sort .Data.Pages "Params.foo.bar" }}
        {{ .Content }}
    {{ end }}

It ignores all leading and trailing dots so "Params.foo.bar" can be
written in ".Params.foo.bar"

This also fixes the issue that 'sort' cannot evaluate a pointer value.

Fix #1330

tpl/template_funcs.go

@@ -882,32 +882,51 @@ func Sort(seq interface{}, args ...interface{}) (interface{}, error) {
 		return nil, errors.New("can't iterate over a nil value")
 	}
 
+	switch seqv.Kind() {
+	case reflect.Array, reflect.Slice, reflect.Map:
+		// ok
+	default:
+		return nil, errors.New("can't sort " + reflect.ValueOf(seq).Type().String())
+	}
+
 	// Create a list of pairs that will be used to do the sort
 	p := pairList{SortAsc: true, SliceType: reflect.SliceOf(seqv.Type().Elem())}
 	p.Pairs = make([]pair, seqv.Len())
 
+	var sortByField string
 	for i, l := range args {
 		dStr, err := cast.ToStringE(l)
 		switch {
 		case i == 0 && err != nil:
-			p.SortByField = ""
+			sortByField = ""
 		case i == 0 && err == nil:
-			p.SortByField = dStr
+			sortByField = dStr
 		case i == 1 && err == nil && dStr == "desc":
 			p.SortAsc = false
 		case i == 1:
 			p.SortAsc = true
 		}
 	}
+	path := strings.Split(strings.Trim(sortByField, "."), ".")
 
 	switch seqv.Kind() {
 	case reflect.Array, reflect.Slice:
 		for i := 0; i < seqv.Len(); i++ {
 			p.Pairs[i].Key = reflect.ValueOf(i)
 			p.Pairs[i].Value = seqv.Index(i)
+			if sortByField == "" || sortByField == "value" {
+				p.Pairs[i].SortByValue = p.Pairs[i].Value
+			} else {
+				v := p.Pairs[i].Value
+				var err error
+				for _, elemName := range path {
+					v, err = evaluateSubElem(v, elemName)
+					if err != nil {
+						return nil, err
+					}
+				}
+				p.Pairs[i].SortByValue = v
 			}
-		if p.SortByField == "" {
-			p.SortByField = "value"
 		}
 
 	case reflect.Map:
@@ -915,10 +934,22 @@ func Sort(seq interface{}, args ...interface{}) (interface{}, error) {
 		for i := 0; i < seqv.Len(); i++ {
 			p.Pairs[i].Key = keys[i]
 			p.Pairs[i].Value = seqv.MapIndex(keys[i])
+			if sortByField == "" {
+				p.Pairs[i].SortByValue = p.Pairs[i].Key
+			} else if sortByField == "value" {
+				p.Pairs[i].SortByValue = p.Pairs[i].Value
+			} else {
+				v := p.Pairs[i].Value
+				var err error
+				for _, elemName := range path {
+					v, err = evaluateSubElem(v, elemName)
+					if err != nil {
+						return nil, err
+					}
+				}
+				p.Pairs[i].SortByValue = v
+			}
 		}
-
-	default:
-		return nil, errors.New("can't sort " + reflect.ValueOf(seq).Type().String())
 	}
 	return p.sort(), nil
 }
@@ -929,12 +960,12 @@ func Sort(seq interface{}, args ...interface{}) (interface{}, error) {
 type pair struct {
 	Key         reflect.Value
 	Value       reflect.Value
+	SortByValue reflect.Value
 }
 
 // A slice of pairs that implements sort.Interface to sort by Value.
 type pairList struct {
 	Pairs     []pair
-	SortByField string
 	SortAsc   bool
 	SliceType reflect.Type
 }
@@ -942,25 +973,7 @@ type pairList struct {
 func (p pairList) Swap(i, j int) { p.Pairs[i], p.Pairs[j] = p.Pairs[j], p.Pairs[i] }
 func (p pairList) Len() int      { return len(p.Pairs) }
 func (p pairList) Less(i, j int) bool {
-	var truth bool
+	return Lt(p.Pairs[i].SortByValue.Interface(), p.Pairs[j].SortByValue.Interface())
-	switch {
-	case p.SortByField == "value":
-		iVal := p.Pairs[i].Value
-		jVal := p.Pairs[j].Value
-		truth = Lt(iVal.Interface(), jVal.Interface())
-
-	case p.SortByField != "":
-		if p.Pairs[i].Value.FieldByName(p.SortByField).IsValid() {
-			iVal := p.Pairs[i].Value.FieldByName(p.SortByField)
-			jVal := p.Pairs[j].Value.FieldByName(p.SortByField)
-			truth = Lt(iVal.Interface(), jVal.Interface())
-		}
-	default:
-		iVal := p.Pairs[i].Key
-		jVal := p.Pairs[j].Key
-		truth = Lt(iVal.Interface(), jVal.Interface())
-	}
-	return truth
 }
 
 // sorts a pairList and returns a slice of sorted values

tpl/template_funcs_test.go

@@ -1081,6 +1081,10 @@ func TestSort(t *testing.T) {
 		MyFloat  float64
 		MyString string
 	}
+	type mid struct {
+		Tst TstX
+	}
+
 	for i, this := range []struct {
 		sequence    interface{}
 		sortByField interface{}
@@ -1091,6 +1095,8 @@ func TestSort(t *testing.T) {
 		{[]string{"class3", "class1", "class2"}, nil, "asc", []string{"class1", "class2", "class3"}},
 		{[]int{1, 2, 3, 4, 5}, nil, "asc", []int{1, 2, 3, 4, 5}},
 		{[]int{5, 4, 3, 1, 2}, nil, "asc", []int{1, 2, 3, 4, 5}},
+		// test sort key parameter is focibly set empty
+		{[]string{"class3", "class1", "class2"}, map[int]string{1: "a"}, "asc", []string{"class1", "class2", "class3"}},
 		// test map sorting by keys
 		{map[string]int{"1": 10, "2": 20, "3": 30, "4": 40, "5": 50}, nil, "asc", []int{10, 20, 30, 40, 50}},
 		{map[string]int{"3": 10, "2": 20, "1": 30, "4": 40, "5": 50}, nil, "asc", []int{30, 20, 10, 40, 50}},
@@ -1122,9 +1128,124 @@ func TestSort(t *testing.T) {
 			"asc",
 			[]ts{{50, 50.5, "fifty"}, {40, 40.5, "forty"}, {10, 10.5, "ten"}, {30, 30.5, "thirty"}, {20, 20.5, "twenty"}},
 		},
-		// Test sort desc
+		// test sort desc
 		{[]string{"class1", "class2", "class3"}, "value", "desc", []string{"class3", "class2", "class1"}},
 		{[]string{"class3", "class1", "class2"}, "value", "desc", []string{"class3", "class2", "class1"}},
+		// test sort by struct's method
+		{
+			[]TstX{{A: "i", B: "j"}, {A: "e", B: "f"}, {A: "c", B: "d"}, {A: "g", B: "h"}, {A: "a", B: "b"}},
+			"TstRv",
+			"asc",
+			[]TstX{{A: "a", B: "b"}, {A: "c", B: "d"}, {A: "e", B: "f"}, {A: "g", B: "h"}, {A: "i", B: "j"}},
+		},
+		{
+			[]*TstX{{A: "i", B: "j"}, {A: "e", B: "f"}, {A: "c", B: "d"}, {A: "g", B: "h"}, {A: "a", B: "b"}},
+			"TstRp",
+			"asc",
+			[]*TstX{{A: "a", B: "b"}, {A: "c", B: "d"}, {A: "e", B: "f"}, {A: "g", B: "h"}, {A: "i", B: "j"}},
+		},
+		// test map sorting by struct's method
+		{
+			map[string]TstX{"1": {A: "i", B: "j"}, "2": {A: "e", B: "f"}, "3": {A: "c", B: "d"}, "4": {A: "g", B: "h"}, "5": {A: "a", B: "b"}},
+			"TstRv",
+			"asc",
+			[]TstX{{A: "a", B: "b"}, {A: "c", B: "d"}, {A: "e", B: "f"}, {A: "g", B: "h"}, {A: "i", B: "j"}},
+		},
+		{
+			map[string]*TstX{"1": {A: "i", B: "j"}, "2": {A: "e", B: "f"}, "3": {A: "c", B: "d"}, "4": {A: "g", B: "h"}, "5": {A: "a", B: "b"}},
+			"TstRp",
+			"asc",
+			[]*TstX{{A: "a", B: "b"}, {A: "c", B: "d"}, {A: "e", B: "f"}, {A: "g", B: "h"}, {A: "i", B: "j"}},
+		},
+		// test sort by dot chaining key argument
+		{
+			[]map[string]TstX{{"foo": TstX{A: "e", B: "f"}}, {"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}},
+			"foo.A",
+			"asc",
+			[]map[string]TstX{{"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}, {"foo": TstX{A: "e", B: "f"}}},
+		},
+		{
+			[]map[string]TstX{{"foo": TstX{A: "e", B: "f"}}, {"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}},
+			".foo.A",
+			"asc",
+			[]map[string]TstX{{"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}, {"foo": TstX{A: "e", B: "f"}}},
+		},
+		{
+			[]map[string]TstX{{"foo": TstX{A: "e", B: "f"}}, {"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}},
+			"foo.TstRv",
+			"asc",
+			[]map[string]TstX{{"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}, {"foo": TstX{A: "e", B: "f"}}},
+		},
+		{
+			[]map[string]*TstX{{"foo": &TstX{A: "e", B: "f"}}, {"foo": &TstX{A: "a", B: "b"}}, {"foo": &TstX{A: "c", B: "d"}}},
+			"foo.TstRp",
+			"asc",
+			[]map[string]*TstX{{"foo": &TstX{A: "a", B: "b"}}, {"foo": &TstX{A: "c", B: "d"}}, {"foo": &TstX{A: "e", B: "f"}}},
+		},
+		{
+			[]map[string]mid{{"foo": mid{Tst: TstX{A: "e", B: "f"}}}, {"foo": mid{Tst: TstX{A: "a", B: "b"}}}, {"foo": mid{Tst: TstX{A: "c", B: "d"}}}},
+			"foo.Tst.A",
+			"asc",
+			[]map[string]mid{{"foo": mid{Tst: TstX{A: "a", B: "b"}}}, {"foo": mid{Tst: TstX{A: "c", B: "d"}}}, {"foo": mid{Tst: TstX{A: "e", B: "f"}}}},
+		},
+		{
+			[]map[string]mid{{"foo": mid{Tst: TstX{A: "e", B: "f"}}}, {"foo": mid{Tst: TstX{A: "a", B: "b"}}}, {"foo": mid{Tst: TstX{A: "c", B: "d"}}}},
+			"foo.Tst.TstRv",
+			"asc",
+			[]map[string]mid{{"foo": mid{Tst: TstX{A: "a", B: "b"}}}, {"foo": mid{Tst: TstX{A: "c", B: "d"}}}, {"foo": mid{Tst: TstX{A: "e", B: "f"}}}},
+		},
+		// test map sorting by dot chaining key argument
+		{
+			map[string]map[string]TstX{"1": {"foo": TstX{A: "e", B: "f"}}, "2": {"foo": TstX{A: "a", B: "b"}}, "3": {"foo": TstX{A: "c", B: "d"}}},
+			"foo.A",
+			"asc",
+			[]map[string]TstX{{"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}, {"foo": TstX{A: "e", B: "f"}}},
+		},
+		{
+			map[string]map[string]TstX{"1": {"foo": TstX{A: "e", B: "f"}}, "2": {"foo": TstX{A: "a", B: "b"}}, "3": {"foo": TstX{A: "c", B: "d"}}},
+			".foo.A",
+			"asc",
+			[]map[string]TstX{{"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}, {"foo": TstX{A: "e", B: "f"}}},
+		},
+		{
+			map[string]map[string]TstX{"1": {"foo": TstX{A: "e", B: "f"}}, "2": {"foo": TstX{A: "a", B: "b"}}, "3": {"foo": TstX{A: "c", B: "d"}}},
+			"foo.TstRv",
+			"asc",
+			[]map[string]TstX{{"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}, {"foo": TstX{A: "e", B: "f"}}},
+		},
+		{
+			map[string]map[string]*TstX{"1": {"foo": &TstX{A: "e", B: "f"}}, "2": {"foo": &TstX{A: "a", B: "b"}}, "3": {"foo": &TstX{A: "c", B: "d"}}},
+			"foo.TstRp",
+			"asc",
+			[]map[string]*TstX{{"foo": &TstX{A: "a", B: "b"}}, {"foo": &TstX{A: "c", B: "d"}}, {"foo": &TstX{A: "e", B: "f"}}},
+		},
+		{
+			map[string]map[string]mid{"1": {"foo": mid{Tst: TstX{A: "e", B: "f"}}}, "2": {"foo": mid{Tst: TstX{A: "a", B: "b"}}}, "3": {"foo": mid{Tst: TstX{A: "c", B: "d"}}}},
+			"foo.Tst.A",
+			"asc",
+			[]map[string]mid{{"foo": mid{Tst: TstX{A: "a", B: "b"}}}, {"foo": mid{Tst: TstX{A: "c", B: "d"}}}, {"foo": mid{Tst: TstX{A: "e", B: "f"}}}},
+		},
+		{
+			map[string]map[string]mid{"1": {"foo": mid{Tst: TstX{A: "e", B: "f"}}}, "2": {"foo": mid{Tst: TstX{A: "a", B: "b"}}}, "3": {"foo": mid{Tst: TstX{A: "c", B: "d"}}}},
+			"foo.Tst.TstRv",
+			"asc",
+			[]map[string]mid{{"foo": mid{Tst: TstX{A: "a", B: "b"}}}, {"foo": mid{Tst: TstX{A: "c", B: "d"}}}, {"foo": mid{Tst: TstX{A: "e", B: "f"}}}},
+		},
+		// test error cases
+		{(*[]TstX)(nil), nil, "asc", false},
+		{TstX{A: "a", B: "b"}, nil, "asc", false},
+		{
+			[]map[string]TstX{{"foo": TstX{A: "e", B: "f"}}, {"foo": TstX{A: "a", B: "b"}}, {"foo": TstX{A: "c", B: "d"}}},
+			"foo.NotAvailable",
+			"asc",
+			false,
+		},
+		{
+			map[string]map[string]TstX{"1": {"foo": TstX{A: "e", B: "f"}}, "2": {"foo": TstX{A: "a", B: "b"}}, "3": {"foo": TstX{A: "c", B: "d"}}},
+			"foo.NotAvailable",
+			"asc",
+			false,
+		},
 	} {
 		var result interface{}
 		var err error
@@ -1133,6 +1254,12 @@ func TestSort(t *testing.T) {
 		} else {
 			result, err = Sort(this.sequence, this.sortByField, this.sortAsc)
 		}
+
+		if b, ok := this.expect.(bool); ok && !b {
+			if err == nil {
+				t.Errorf("[%d] Sort didn't return an expected error", i)
+			}
+		} else {
 			if err != nil {
 				t.Errorf("[%d] failed: %s", i, err)
 				continue
@@ -1141,6 +1268,7 @@ func TestSort(t *testing.T) {
 				t.Errorf("[%d] Sort called on sequence: %v | sortByField: `%v` | got %v but expected %v", i, this.sequence, this.sortByField, result, this.expect)
 			}
 		}
+	}
 }
 
 func TestReturnWhenSet(t *testing.T) {