Fix slice on multiline strings

cmd/liquid/main.go

@@ -4,8 +4,8 @@
 //
 // Examples:
 //
-// 	echo '{{ "Hello " | append: "World" }}' | liquid
-// 	liquid source.tpl
+//	echo '{{ "Hello " | append: "World" }}' | liquid
+//	liquid source.tpl
 package main
 
 import (

engine.go

@@ -43,7 +43,6 @@ func (e *Engine) RegisterBlock(name string, td Renderer) {
 // * https://github.com/osteele/liquid/blob/master/filters/filters.go
 //
 // * https://github.com/osteele/gojekyll/blob/master/filters/filters.go
-//
 func (e *Engine) RegisterFilter(name string, fn interface{}) {
 	e.cfg.AddFilter(name, fn)
 }

filters/standard_filters.go

@@ -12,7 +12,6 @@ import (
 	"strings"
 	"time"
 	"unicode"
-	"unicode/utf8"
 
 	"github.com/osteele/liquid/values"
 	"github.com/osteele/tuesday"
@@ -147,13 +146,16 @@ func AddStandardFilters(fd FilterDictionary) { // nolint: gocyclo
 	})
 	fd.AddFilter("sort_natural", sortNaturalFilter)
 	fd.AddFilter("slice", func(s string, start int, length func(int) int) string {
-		// runes aren't bytes; don't use slice
+		ss := []rune(s)
 		n := length(1)
 		if start < 0 {
-			start = utf8.RuneCountInString(s) + start
+			start = len(ss) + start
+		}
+		end := start + n
+		if end > len(ss) {
+			end = len(ss)
 		}
-		p := regexp.MustCompile(fmt.Sprintf(`^.{%d}(.{0,%d}).*$`, start, n))
-		return p.ReplaceAllString(s, "$1")
+		return string(ss[start:end])
 	})
 	fd.AddFilter("split", splitFilter)
 	fd.AddFilter("strip_html", func(s string) string {

filters/standard_filters_test.go

@@ -97,8 +97,12 @@ var filterTests = []struct {
 	{`"I strained to see the train through the rain" | remove_first: "rain"`, "I sted to see the train through the rain"},
 
 	{`"Liquid" | slice: 0`, "L"},
+	{`"Liquid
+Liquid" | slice: 0`, "L"},
 	{`"Liquid" | slice: 2`, "q"},
 	{`"Liquid" | slice: 2, 5`, "quid"},
+	{`"Liquid
+Liquid" | slice: 2, 4`, "quid"},
 	{`"Liquid" | slice: -3, 2`, "ui"},
 
 	{`"a/b/c" | split: '/' | join: '-'`, "a-b-c"},

liquid.go

@@ -3,7 +3,6 @@ Package liquid is a pure Go implementation of Shopify Liquid templates, develope
 
 See the project README https://github.com/osteele/liquid for additional information and implementation status.
 
-
 The liquid package itself is versioned in gopkg.in. Subpackages have no compatibility guarantees. Except where specifically documented, the “public” entities of subpackages are intended only for use by the liquid package and its subpackages.
 */
 package liquid