[clang] [-Wunsafe-buffer-usage] Warning Libc functions (PR #101583)

[Ziqing Luo via cfe-commits]

================
@@ -12383,6 +12383,13 @@ def warn_unsafe_buffer_operation : Warning<
   "%select{unsafe pointer operation|unsafe pointer arithmetic|"
   "unsafe buffer access|function introduces unsafe buffer manipulation|unsafe invocation of span::data}0">,
   InGroup<UnsafeBufferUsage>, DefaultIgnore;
+def warn_unsafe_buffer_libc_call : Warning<
+  "function %0 introduces unsafe buffer access">,
+  InGroup<UnsafeBufferUsage>, DefaultIgnore;
+def note_unsafe_buffer_printf_call : Note<
+  "%select{| change to 'snprintf' for explicit bounds checking | buffer pointer and size may not match"
+          "| use 'std::string::c_str' or string literal as string pointer to guarantee null-termination"
----------------
ziqingluo-90 wrote:

> Have we tried getting data from a real project?

Yes! Basically these special handlings are all corresponding to actual cases in our downstream projects.

>I think for this warning in particular, it's valuable to point the user to the specific %s argument. To, at least, make sure that they know we don't mean the snprintf's target string or something.

I will let the notes point to specific argument source locations.  For better note messages, we could do it in a follow-up patch?

https://github.com/llvm/llvm-project/pull/101583