Fix shortcode detection in RenderString

Fixes #10654

parser/pageparser/pageparser.go

@@ -19,6 +19,8 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"regexp"
+	"strings"
 
 	"github.com/gohugoio/hugo/parser/metadecoders"
 )
@@ -234,3 +236,14 @@ func IsProbablySourceOfItems(source []byte, items Items) bool {
 
 	return true
 }
+
+var hasShortcodeRe = regexp.MustCompile(`{{[%,<][^\/]`)
+
+// HasShortcode returns true if the given string contains a shortcode.
+func HasShortcode(s string) bool {
+	// Fast path for the common case.
+	if !strings.Contains(s, "{{") {
+		return false
+	}
+	return hasShortcodeRe.MatchString(s)
+}

parser/pageparser/pageparser_test.go

@@ -101,3 +101,30 @@ func TestIsProbablyItemsSource(t *testing.T) {
 	c.Assert(IsProbablySourceOfItems([]byte(`{{< foo >}}  `), items), qt.IsFalse)
 	c.Assert(IsProbablySourceOfItems([]byte(``), items), qt.IsFalse)
 }
+
+func TestHasShortcode(t *testing.T) {
+	c := qt.New(t)
+
+	c.Assert(HasShortcode("{{< foo >}}"), qt.IsTrue)
+	c.Assert(HasShortcode("aSDasd  SDasd aSD\n\nasdfadf{{% foo %}}\nasdf"), qt.IsTrue)
+	c.Assert(HasShortcode("{{</* foo */>}}"), qt.IsFalse)
+	c.Assert(HasShortcode("{{%/* foo */%}}"), qt.IsFalse)
+
+}
+
+func BenchmarkHasShortcode(b *testing.B) {
+	withShortcode := strings.Repeat("this is text", 30) + "{{< myshortcode >}}This is some inner content.{{< /myshortcode >}}" + strings.Repeat("this is text", 30)
+	withoutShortcode := strings.Repeat("this is text", 30) + "This is some inner content." + strings.Repeat("this is text", 30)
+	b.Run("Match", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			HasShortcode(withShortcode)
+		}
+	})
+
+	b.Run("NoMatch", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			HasShortcode(withoutShortcode)
+		}
+	})
+
+}