From 9de6468701f4def1bbdc737e8ad1327f2cfaecc8 Mon Sep 17 00:00:00 2001
From: Damien Neil <dneil@google.com>
Date: Mon, 8 Dec 2025 13:54:15 -0800
Subject: [PATCH] json/jsontext: normalize all invalid Kinds to 0

For #75431

Change-Id: Iafefe952d3c1837e2f4c8c24cae96945d9e5abbf
Reviewed-on: https://go-review.googlesource.com/c/go/+/728380
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
---
 src/encoding/json/jsontext/decode_test.go |  4 +--
 src/encoding/json/jsontext/token.go       | 31 +++++++++++++++++++----
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/src/encoding/json/jsontext/decode_test.go b/src/encoding/json/jsontext/decode_test.go
index 209ff65ec8..3f48cae2d1 100644
--- a/src/encoding/json/jsontext/decode_test.go
+++ b/src/encoding/json/jsontext/decode_test.go
@@ -193,8 +193,8 @@ var decoderErrorTestdata = []struct {
 	name: jsontest.Name("InvalidStart"),
 	in:   ` #`,
 	calls: []decoderMethodCall{
-		{'#', zeroToken, newInvalidCharacterError("#", "at start of value").withPos(" ", ""), ""},
-		{'#', zeroValue, newInvalidCharacterError("#", "at start of value").withPos(" ", ""), ""},
+		{0, zeroToken, newInvalidCharacterError("#", "at start of value").withPos(" ", ""), ""},
+		{0, zeroValue, newInvalidCharacterError("#", "at start of value").withPos(" ", ""), ""},
 	},
 }, {
 	name: jsontest.Name("StreamN0"),
diff --git a/src/encoding/json/jsontext/token.go b/src/encoding/json/jsontext/token.go
index e78c3f84d8..caf0174923 100644
--- a/src/encoding/json/jsontext/token.go
+++ b/src/encoding/json/jsontext/token.go
@@ -518,10 +518,31 @@ func (k Kind) String() string {
 	}
 }
 
-// normalize coalesces all possible starting characters of a number as just '0'.
+var normKind = [256]Kind{
+	'n': 'n',
+	'f': 'f',
+	't': 't',
+	'"': '"',
+	'{': '{',
+	'}': '}',
+	'[': '[',
+	']': ']',
+	'-': '0',
+	'0': '0',
+	'1': '0',
+	'2': '0',
+	'3': '0',
+	'4': '0',
+	'5': '0',
+	'6': '0',
+	'7': '0',
+	'8': '0',
+	'9': '0',
+}
+
+// normalize coalesces all possible starting characters of a number as just '0',
+// and converts all invalid kinds to 0.
 func (k Kind) normalize() Kind {
-	if k == '-' || ('0' <= k && k <= '9') {
-		return '0'
-	}
-	return k
+	// A lookup table keeps the inlining cost as low as possible.
+	return normKind[k]
 }
-- 
2.52.0