(C++) Integer literals with quote delimiters in #defines break highlighting · highlightjs/highlight.js#3928

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Description

Describe the issue Integer literals in C++ may be written as 1'000'000'000 instead of 1000000000 for greater readability. When this is used inside a #define, if breaks highlighting which treats the rest of the code as being inside a string.

Which language seems to have the issue? cpp

Are you using highlight or highlightAuto? highlight

Sample Code to Reproduce

#include <iostream>
#define INF 1'000'000'000

int main() {
	int a = INF;
    return 0;
}

Expected behavior The token 1'000'000'000 should be highlighted as a number, and the following code should also be highlighted normally, instead of as if it is inside a string:

Additional context

The snippet below seems to be highlighted fine, so the issue is likely the interplay between quote-separated literals and defines.

#include <iostream>

int f(int x) { return f(2'000); }

int main() {
	int a = 1'000'000'000;
    int b = f(1'000);
    return 0;
}

Contributor guide

Tech stack: javascriptcpp
Domain: frontenddeveloper experience
Issue type: bug
Difficulty: 3
Estimated time: 1-3 hours
Activity status: active
Clarity: clear
Prerequisites: basic understanding of highlight.js language definitionsfamiliarity with regex
Newbie friendliness: 35
Research direction: The bug is in the C++ language grammar of highlight.js. The issue is that integer literals with digit separators (e.g., 1'000'000'000) inside a #define directive break highlighting. The fix likely involves modifying the number pattern in the C++ language definition file (src/languages/cpp.js) to correctly handle digit separators within preprocessing directives. Check how strings are currently being matched; the apostrophe might be interpreted as a string delimiter. Review the existing PR or discussion comments for proposed solutions. The reproduction snippet shows that the issue is specific to #define lines; test with various combinations of defines and literals.