html: use sync.OnceValues instead of var once sync.Once

Simplify populateMaps with sync.OnceValues.

Change-Id: Id52e6e1623c621b8d51e11fecbe3f1fab1e74eb4
GitHub-Last-Rev: 3cf736ae299f14ece401d218d68c3c8870e0cf5a
GitHub-Pull-Request: golang/go#69946
Reviewed-on: https://go-review.googlesource.com/c/go/+/621255
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>

3 files changed, 14 insertions, 20 deletions

diff --git a/src/html/entity.go b/src/html/entity.go
index f0f9a6a973..421a54ab57 100644
--- a/src/html/entity.go
+++ b/src/html/entity.go
@@ -9,22 +9,16 @@ import "sync"
 // All entities that do not end with ';' are 6 or fewer bytes long.
 const longestEntityWithoutSemicolon = 6
 
+// entityMaps returns entity and entity2.
+//
 // entity is a map from HTML entity names to their values. The semicolon matters:
 // https://html.spec.whatwg.org/multipage/named-characters.html
 // lists both "amp" and "amp;" as two separate entries.
-//
 // Note that the HTML5 list is larger than the HTML4 list at
 // http://www.w3.org/TR/html4/sgml/entities.html
-var entity map[string]rune
-
-// HTML entities that are two unicode codepoints.
-var entity2 map[string][2]rune
-
-// populateMapsOnce guards calling populateMaps.
-var populateMapsOnce sync.Once
-
-// populateMaps populates entity and entity2.
-func populateMaps() {
+//
+// entity2 is a map of HTML entities to two unicode codepoints.
+var entityMaps = sync.OnceValues(func() (entity map[string]rune, entity2 map[string][2]rune) {
 	entity = map[string]rune{
 		"AElig;":                           '\U000000C6',
 		"AMP;":                             '\U00000026',
@@ -2262,4 +2256,6 @@ func populateMaps() {
 		"vsupnE;":                  {'\u2ACC', '\uFE00'},
 		"vsupne;":                  {'\u228B', '\uFE00'},
 	}
-}
+
+	return entity, entity2
+})
diff --git a/src/html/entity_test.go b/src/html/entity_test.go
index 6688ed2c43..4011da6141 100644
--- a/src/html/entity_test.go
+++ b/src/html/entity_test.go
@@ -9,11 +9,9 @@ import (
 	"unicode/utf8"
 )
 
-func init() {
-	UnescapeString("") // force load of entity maps
-}
-
 func TestEntityLength(t *testing.T) {
+	entity, entity2 := entityMaps()
+
 	if len(entity) == 0 || len(entity2) == 0 {
 		t.Fatal("maps not loaded")
 	}
diff --git a/src/html/escape.go b/src/html/escape.go
index 1dc12873b0..b718c247ff 100644
--- a/src/html/escape.go
+++ b/src/html/escape.go
@@ -53,7 +53,7 @@ var replacementTable = [...]rune{
 // unescapeEntity reads an entity like "<" from b[src:] and writes the
 // corresponding "<" to b[dst:], returning the incremented dst and src cursors.
 // Precondition: b[src] == '&' && dst <= src.
-func unescapeEntity(b []byte, dst, src int) (dst1, src1 int) {
+func unescapeEntity(b []byte, dst, src int, entity map[string]rune, entity2 map[string][2]rune) (dst1, src1 int) {
 	const attribute = false
 
 	// http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#consume-a-character-reference
@@ -185,7 +185,6 @@ func EscapeString(s string) string {
 // UnescapeString(EscapeString(s)) == s always holds, but the converse isn't
 // always true.
 func UnescapeString(s string) string {
-	populateMapsOnce.Do(populateMaps)
 	i := strings.IndexByte(s, '&')
 
 	if i < 0 {
@@ -193,7 +192,8 @@ func UnescapeString(s string) string {
 	}
 
 	b := []byte(s)
-	dst, src := unescapeEntity(b, i, i)
+	entity, entity2 := entityMaps()
+	dst, src := unescapeEntity(b, i, i, entity, entity2)
 	for len(s[src:]) > 0 {
 		if s[src] == '&' {
 			i = 0
@@ -208,7 +208,7 @@ func UnescapeString(s string) string {
 		if i > 0 {
 			copy(b[dst:], s[src:src+i])
 		}
-		dst, src = unescapeEntity(b, dst+i, src+i)
+		dst, src = unescapeEntity(b, dst+i, src+i, entity, entity2)
 	}
 	return string(b[:dst])
 }