Thank you for the patch, and for caring about bounded string operations. The intent is good, but I cannot merge this as it stands, because strlcpy and strlcat are not portable enough for mruby's targets.

These two functions are BSD extensions, not part of standard C. They exist on the BSDs and macOS, on musl, and on glibc only since 2.38 (2023). They are absent on older glibc (for example Ubuntu 22.04 ships glibc 2.35), on MSVC, usually on MinGW's msvcrt, and on many embedded libcs. mruby explicitly supports embedded targets, so we cannot assume the C library provides them.

This is not only a link-time issue. mruby compiles C with -Werror-implicit-function-declaration, so on any platform whose <string.h> does not declare these functions, the build fails at compile time rather than warning. Our CI already covers such platforms (Ubuntu 22.04 gcc/clang, Windows MSVC), and this change touches core files that every build compiles, including embedded ones: src/numeric.c (mrb_float_to_str) and mrbgems/mruby-compiler/src/diagnostic.c.

To take this improvement, mruby first needs its own portable strlcpy/strlcat: a fallback implementation used when the C library does not provide them, selected by feature detection. Once that is in place, the call sites here can use them safely. Alternatively, the bounded copies can be written with snprintf, which is portable.

I would be happy to take a revised version along those lines. Thanks again.

Thank you for the review!
I added macros MRB_STRLCPY and MRB_STRLCAT to provide fallbacks via snprintf.

Reference links for the conditionals (brief notes in comments):

• __POSIX_VISIBLE and __BSD_VISIBLE: OpenBSD's string.h
• POSIX.1-2024 issue 8 changes: the section which has added strlcpy and strlcat
• __GLIBC__ and __GLIBC_MINOR__: features.h of GNU C library