Add underscore digit separator support for hex literals

Enable hex literals to use underscores as digit separators,
matching ClickHouse's support for numbers like 0xbad_cafe.
Fixed the readNumberOrIdent function which is the code path
used when parsing numbers starting with digits.

Author: claude

lexer/lexer.go

@@ -630,9 +630,10 @@ func (l *Lexer) readNumber() Item {
 		l.readChar()
 		if l.ch == 'x' || l.ch == 'X' {
 			// Hex literal (may include P notation for floats: 0x1p4, 0x1.2p-3)
+			// Also allows underscores as digit separators: 0xbad_cafe
 			sb.WriteRune(l.ch)
 			l.readChar()
-			for isHexDigit(l.ch) {
+			for isHexDigit(l.ch) || l.ch == '_' {
 				sb.WriteRune(l.ch)
 				l.readChar()
 			}
@@ -834,7 +835,8 @@ func (l *Lexer) readNumberOrIdent() Item {
 	if val == "0" && (l.ch == 'x' || l.ch == 'X') {
 		sb.WriteRune(l.ch)
 		l.readChar()
-		for isHexDigit(l.ch) {
+		// Also allow underscores as digit separators: 0xbad_cafe
+		for isHexDigit(l.ch) || l.ch == '_' {
 			sb.WriteRune(l.ch)
 			l.readChar()
 		}

parser/testdata/02354_numeric_literals_with_underscores/metadata.json

@@ -1,6 +1,5 @@
 {
   "explain_todo": {
-    "stmt4": true,
     "stmt5": true,
     "stmt6": true
   }

parser/testdata/02523_array_shuffle/metadata.json

@@ -1,58 +1,11 @@
 {
   "explain_todo": {
-    "stmt10": true,
-    "stmt11": true,
-    "stmt12": true,
-    "stmt13": true,
     "stmt16": true,
     "stmt17": true,
     "stmt18": true,
-    "stmt19": true,
-    "stmt2": true,
-    "stmt20": true,
-    "stmt21": true,
-    "stmt22": true,
-    "stmt25": true,
-    "stmt28": true,
-    "stmt29": true,
-    "stmt30": true,
-    "stmt31": true,
-    "stmt32": true,
-    "stmt33": true,
-    "stmt34": true,
-    "stmt35": true,
-    "stmt36": true,
     "stmt39": true,
-    "stmt4": true,
     "stmt40": true,
-    "stmt41": true,
-    "stmt42": true,
-    "stmt43": true,
-    "stmt44": true,
-    "stmt46": true,
-    "stmt47": true,
-    "stmt48": true,
-    "stmt49": true,
-    "stmt5": true,
-    "stmt50": true,
-    "stmt51": true,
-    "stmt52": true,
-    "stmt53": true,
-    "stmt54": true,
-    "stmt55": true,
-    "stmt56": true,
-    "stmt57": true,
-    "stmt58": true,
-    "stmt59": true,
-    "stmt6": true,
     "stmt60": true,
-    "stmt61": true,
-    "stmt62": true,
-    "stmt63": true,
-    "stmt64": true,
-    "stmt65": true,
-    "stmt7": true,
-    "stmt8": true,
-    "stmt9": true
+    "stmt61": true
   }
 }