Fix crash occurring due to unconverted 'x' flag

The PCRE `(?x)` inline flag did not have a conversion process, causing a crash.

Fixes #16.

Author: Nixinova

changelog.md

@@ -1,5 +1,8 @@
 # Changelog
 
+## Next
+- Fixed a crash occurring when parsing heuristics for `.txt` files ([#16](https://github.com/Nixinova/LinguistJS/issues/16)).
+
 ## 2.5.2
 *2022-06-28*
 - Fixed file extensions with multiple delimiters not being prioritised over basic extensions.

src/helpers/convert-pcre.ts

@@ -10,15 +10,25 @@ export default function pcre(regex: string): RegExp {
 		replace(match, '');
 		[...flags].forEach(flag => finalFlags.add(flag));
 	}
-	// Remove invalid syntax
+	// Remove PCRE-only syntax
 	replace(/([*+]){2}/g, '$1');
 	replace(/\(\?>/g, '(?:');
 	// Remove start/end-of-file markers
 	if (/\\[AZ]/.test(finalRegex)) {
-		replace(/\\A/g, '^').replace(/\\Z/g, '$');
+		replace(/\\A/g, '^');
+		replace(/\\Z/g, '$');
 		finalFlags.delete('m');
 	}
-	else finalFlags.add('m');
+	else {
+		finalFlags.add('m');
+	}
+	// Reformat free-spacing mode
+	if (finalFlags.has('x')) {
+		finalFlags.delete('x');
+		replace(/#.+/g, '');
+		replace(/^\s+|\s+$|\n/gm, '');
+		replace(/\s+/g, ' ');
+	}
 	// Return final regex
 	return RegExp(finalRegex, [...finalFlags].join(''));
 }