From 6cd86876b84b0be02b08db5fdd5046dc73dfb38d Mon Sep 17 00:00:00 2001
From: Cameron Moore <moorereason@gmail.com>
Date: Sat, 4 Dec 2021 15:56:48 -0600
Subject: [PATCH] Decode: ensure signed numbers don't start with an underscore
 (#698)

---
 decode.go           |  9 +++++++--
 unmarshaler_test.go | 10 +++++++++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/decode.go b/decode.go
index e18b911..63a756d 100644
--- a/decode.go
+++ b/decode.go
@@ -386,8 +386,13 @@ func parseIntDec(b []byte) (int64, error) {
 }
 
 func checkAndRemoveUnderscoresIntegers(b []byte) ([]byte, error) {
-	if b[0] == '_' {
-		return nil, newDecodeError(b[0:1], "number cannot start with underscore")
+	start := 0
+	if b[start] == '+' || b[start] == '-' {
+		start++
+	}
+
+	if b[start] == '_' {
+		return nil, newDecodeError(b[start:start+1], "number cannot start with underscore")
 	}
 
 	if b[len(b)-1] == '_' {
diff --git a/unmarshaler_test.go b/unmarshaler_test.go
index 076a441..bfbd6e4 100644
--- a/unmarshaler_test.go
+++ b/unmarshaler_test.go
@@ -2306,9 +2306,17 @@ func TestUnmarshalDecodeErrors(t *testing.T) {
 			data: `flt8 = 224_617.445_991__228`,
 		},
 		{
-			desc: "float with double _",
+			desc: "float with double .",
 			data: `flt8 = 1..2`,
 		},
+		{
+			desc: "number with plus sign and leading underscore",
+			data: `a = +_0`,
+		},
+		{
+			desc: "number with negative sign and leading underscore",
+			data: `a = -_0`,
+		},
 		{
 			desc: "int with wrong base",
 			data: `a = 0f2`,