Critical - P2 The mozjs upgrade uses std::to_chars which Apple's libc++ marks unavailable below macOS 10.15. Backport branches (e.g. v7.0) targeting older macOS fail to compile.
[2026/03/20 23:49:26.434] In file included from src/third_party/mozjs/platform/x86_64/macOS/build/Unified_cpp_js_src14.cpp:47: [2026/03/20 23:49:26.434] src/third_party/mozjs/extract/js/src/vm/JSAtomUtils.cpp:906:22: error: 'to_chars<unsigned int, 0>' is unavailable: introduced in macOS 10.15 [2026/03/20 23:49:26.434] auto result = std::to_chars(buf, buf + std::size(buf), index, 10); [2026/03/20 23:49:26.434] ^ [2026/03/20 23:49:26.434] /Applications/Xcode13.2.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/charconv:401:1: note: 'to_chars<unsigned int, 0>' has been explicitly marked unavailable here [2026/03/20 23:49:26.434] to_chars(char* __first, char* __last, _Tp __value, int __base) [2026/03/20 23:49:26.435] ^
Fix: MONGO_MOZJS_TO_CHARS compat macro in js/src/util/ToCharsCompat.h — portable fallback on macOS < 10.15, delegates to std::to_chars otherwise. Applied in mongodb-forks/spidermonkey.