tpl/strings: Add strings.Count

Fixes #7453

tpl/strings/init.go

@@ -51,6 +51,13 @@ func init() {
 			[][2]string{},
 		)
 
+		ns.AddMethodMapping(ctx.Count,
+			nil,
+			[][2]string{
+				{`{{"aabab" | strings.Count "a" }}`, `3`},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.FindRE,
 			[]string{"findRE"},
 			[][2]string{

tpl/strings/strings.go

@@ -18,6 +18,7 @@ import (
 	"errors"
 	"fmt"
 	"html/template"
+	"strings"
 
 	_strings "strings"
 	"unicode/utf8"
@@ -90,6 +91,20 @@ func (ns *Namespace) CountWords(s interface{}) (int, error) {
 	return counter, nil
 }
 
+// Count counts the number of non-overlapping instances of substr in s.
+// If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
+func (ns *Namespace) Count(substr, s interface{}) (int, error) {
+	substrs, err := cast.ToStringE(substr)
+	if err != nil {
+		return 0, _errors.Wrap(err, "Failed to convert substr to string")
+	}
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return 0, _errors.Wrap(err, "Failed to convert s to string")
+	}
+	return strings.Count(ss, substrs), nil
+}
+
 // Chomp returns a copy of s with all trailing newline characters removed.
 func (ns *Namespace) Chomp(s interface{}) (interface{}, error) {
 	ss, err := cast.ToStringE(s)