text/template: support range-over-func

Fixes #66107

Change-Id: If3e503efca200aa86463c9d27d06986b03c0d638

Author: qiulaidongfeng

src/text/template/exec.go

@@ -394,6 +394,25 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 		}()
 		s.walk(elem, r.List)
 	}
+
+	rangeone := func(elem reflect.Value) {
+		if len(r.Pipe.Decl) > 0 {
+			s.setVar(r.Pipe.Decl[0].Ident[0], elem)
+		}
+		if len(r.Pipe.Decl) > 1 {
+			s.errorf("can't use %v iterate over two variables", val)
+			return
+		}
+		defer s.pop(mark)
+		defer func() {
+			// Consume panic(walkContinue)
+			if r := recover(); r != nil && r != walkContinue {
+				panic(r)
+			}
+		}()
+		s.walk(elem, r.List)
+	}
+
 	switch val.Kind() {
 	case reflect.Array, reflect.Slice:
 		if val.Len() == 0 {
@@ -434,6 +453,20 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 		return
 	case reflect.Invalid:
 		break // An invalid value is likely a nil map, etc. and acts like an empty map.
+	case reflect.Func:
+		if val.Type().CanSeq() {
+			for v := range val.Seq() {
+				rangeone(v)
+			}
+			return
+		}
+		if val.Type().CanSeq2() {
+			for i, v := range val.Seq2() {
+				oneIteration(reflect.ValueOf(i), v)
+			}
+			return
+		}
+		fallthrough
 	default:
 		s.errorf("range can't iterate over %v", val)
 	}

src/text/template/exec_test.go

@@ -601,6 +601,27 @@ var execTests = []execTest{
 	{"declare in range", "{{range $x := .PSI}}<{{$foo:=$x}}{{$x}}>{{end}}", "<21><22><23>", tVal, true},
 	{"range count", `{{range $i, $x := count 5}}[{{$i}}]{{$x}}{{end}}`, "[0]a[1]b[2]c[3]d[4]e", tVal, true},
 	{"range nil count", `{{range $i, $x := count 0}}{{else}}empty{{end}}`, "empty", tVal, true},
+	{"range iter.Seq[int]", `{{range $i := .}}{{$i}}{{end}}`, "01", func(yield func(int) bool) {
+		for i := range 2 {
+			if !yield(i) {
+				break
+			}
+		}
+	}, true},
+	{"range iter.Seq[int]", `{{range $i, $c := .}}{{$c}}{{end}}`, "", func(yield func(int) bool) {
+		for i := range 2 {
+			if !yield(i) {
+				break
+			}
+		}
+	}, false},
+	{"range iter.Seq[int,int]", `{{range $i, $c := .}}{{$i}}{{$c}}{{end}}`, "0112", func(yield func(int, int) bool) {
+		for i := range 2 {
+			if !yield(i, i+1) {
+				break
+			}
+		}
+	}, true},
 
 	// Cute examples.
 	{"or as if true", `{{or .SI "slice is empty"}}`, "[3 4 5]", tVal, true},