Handle question marks in model lexer, closes #15879

src/grammar/RustLexer.g4

@@ -194,8 +194,13 @@ LIT_STR_RAW
   : 'r' LIT_STR_RAW_INNER SUFFIX?
   ;
 
+
+QUESTION : '?';
+
 IDENT : XID_start XID_continue* ;
 
+fragment QUESTION_IDENTIFIER : QUESTION? IDENT;
+
 LIFETIME : '\'' IDENT ;
 
 WHITESPACE : [ \r\n\t]+ ;

src/grammar/verify.rs

@@ -107,6 +107,7 @@ fn parse_token_list(file: &str) -> HashMap<String, token::Token> {
             "LE"                => token::Le,
             "LIT_BINARY"        => token::Literal(token::Binary(Name(0)), None),
             "LIT_BINARY_RAW"    => token::Literal(token::BinaryRaw(Name(0), 0), None),
+            "QUESTION"          => token::Question,
             _                   => continue,
         };