From 5c78d08583752a97147a7656ff329b75ce0e1ec6 Mon Sep 17 00:00:00 2001
From: Eric Prud'hommeaux <eric@uu3.org>
Date: Sat, 18 Mar 2023 19:40:04 +0100
Subject: [PATCH] RE group production emits a non-captured group

For deep lexer rules like [ShEx's PN_CHARS_BASE](https://github.com/shexjs/shex.js/blob/b5cb30708d7c69550a07f1329aaf97cdb8eed737/packages/shex-parser/lib/ShExJison.jison#L255), the [emitted rule](https://github.com/shexjs/shex.js/blob/b5cb30708d7c69550a07f1329aaf97cdb8eed737/packages/shex-parser/lib/ShExJison.js#L934) has an enormous number of capture groups. When parsing a large input like [FHIR.shex](https://hl7.org/fhir/R4B/fhir.schema.shex.zip) gives a stack error:
```
/home/eric/checkouts/shexSpec/shex.js/packages/shex-parser/shex-parser.js:251
      throw errors[0];
      ^

RangeError: Maximum call stack size exceeded
    at String.match (<anonymous>)
    at JisonLexer.next (/home/eric/checkouts/shexSpec/shex.js/node_modules/@ts-jison/lexer/lib/lexer.js:225:37)
    at JisonLexer.lex (/home/eric/checkouts/shexSpec/shex.js/node_modules/@ts-jison/lexer/lib/lexer.js:269:22)
    at JisonLexer.lex (/home/eric/checkouts/shexSpec/shex.js/node_modules/@ts-jison/lexer/lib/lexer.js:274:25)
    at lex (/home/eric/checkouts/shexSpec/shex.js/node_modules/@ts-jison/parser/lib/parser.js:51:28)
    at JisonParser.parse (/home/eric/checkouts/shexSpec/shex.js/node_modules/@ts-jison/parser/lib/parser.js:68:30)
    at ShExJisonParser.runParser [as parse] (/home/eric/checkouts/shexSpec/shex.js/packages/shex-parser/shex-parser.js:231:22)
    at Object.<anonymous> (/home/eric/checkouts/shexSpec/shex.js/parseFhir.js:10:38)
    at Module._compile (node:internal/modules/cjs/loader:1119:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1173:10) {
  parsed: null
}
```
Eliminating capture groups fixes the problem and makes parsing wayyyy faster.

(I generated this grammar using ts-jison, but the same happens with jison.)
---
 lex.y | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lex.y b/lex.y
index 599c382..4865b8f 100644
--- a/lex.y
+++ b/lex.y
@@ -156,7 +156,7 @@ regex_concat
 
 regex_base
     : '(' regex_list ')'
-        { $$ = '(' + $2 + ')'; }
+        { $$ = '(?:' + $2 + ')'; }
     | SPECIAL_GROUP regex_list ')'
         { $$ = $1 + $2 + ')'; }
     | regex_base '+'