tpl: Fix strings/truncate CJK handling

Fix truncate position for mix of CJK and non-CJK text.

Fixes #14039

Author: oishikazuo

tpl/strings/truncate.go

@@ -111,7 +111,11 @@ func (ns *Namespace) Truncate(s any, options ...any) (template.HTML, error) {
 		if unicode.IsSpace(r) {
 			lastWordIndex = lastNonSpace
 		} else if unicode.In(r, unicode.Han, unicode.Hangul, unicode.Hiragana, unicode.Katakana) {
-			lastWordIndex = i
+			lastWordIndex = lastNonSpace
+			lastNonSpace = i + utf8.RuneLen(r)
+			if currentLen <= length {
+				lastWordIndex = lastNonSpace
+			}
 		} else {
 			lastNonSpace = i + utf8.RuneLen(r)
 		}

tpl/strings/truncate_test.go

@@ -41,6 +41,19 @@ func TestTruncate(t *testing.T) {
 		{10, template.HTML("<p>IamanextremelylongwordthatjustgoesonandonandonjusttoannoyyoualmostasifIwaswritteninGermanActuallyIbettheresagermanwordforthis</p>"), nil, template.HTML("<p>Iamanextre …</p>"), false},
 		{13, template.HTML("With <a href=\"/markdown\">Markdown</a> inside."), nil, template.HTML("With <a href=\"/markdown\">Markdown …</a>"), false},
 		{14, "Hello中国 Good 好的", nil, template.HTML("Hello中国 Good 好 …"), false},
+		{12, "", "日本語でHugoを使います", template.HTML("日本語でHugoを使いま"), false},
+		{12, "", "日本語で Hugo を使います", template.HTML("日本語で Hugo を使"), false},
+		{8, "", "日本語でHugoを使います", template.HTML("日本語でHugo"), false},
+		{10, "", "日本語で Hugo を使います", template.HTML("日本語で Hugo"), false},
+		{9, "", "日本語で Hugo を使います", template.HTML("日本語で Hugo"), false},
+		{7, "", "日本語でHugoを使います", template.HTML("日本語で"), false},
+		{7, "", "日本語で Hugo を使います", template.HTML("日本語で"), false},
+		{6, "", "日本語でHugoを使います", template.HTML("日本語で"), false},
+		{6, "", "日本語で Hugo を使います", template.HTML("日本語で"), false},
+		{5, "", "日本語でHugoを使います", template.HTML("日本語で"), false},
+		{5, "", "日本語で Hugo を使います", template.HTML("日本語で"), false},
+		{4, "", "日本語でHugoを使います", template.HTML("日本語で"), false},
+		{4, "", "日本語で Hugo を使います", template.HTML("日本語で"), false},
 		{15, "", template.HTML("A <br> tag that's not closed"), template.HTML("A <br> tag that's"), false},
 		{14, template.HTML("<p>Hello中国 Good 好的</p>"), nil, template.HTML("<p>Hello中国 Good 好 …</p>"), false},
 		{2, template.HTML("<p>P1</p><p>P2</p>"), nil, template.HTML("<p>P1 …</p>"), false},