[-Wunsafe-buffer-usage] add test for constexpr size in snprintf (#119786)

[tsepez]

Add a test for passing a constexpr size argument to snprintf()
giving an unsafe buffers warning.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Thomas Sepez (tsepez)

Changes

Add a test for passing a constexpr size argument to snprintf()
giving an unsafe buffers warning.

---

Full diff: https://github.com/llvm/llvm-project/pull/126826.diff

1 Files Affected:

• (modified) clang/test/SemaCXX/warn-unsafe-buffer-usage-libc-functions.cpp (+3-2)

diff --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage-libc-functions.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage-libc-functions.cpp
index a7c19bcac1607..40e1e1fbf41a7 100644
--- a/clang/test/SemaCXX/warn-unsafe-buffer-usage-libc-functions.cpp
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage-libc-functions.cpp
@@ -97,11 +97,12 @@ void f(char * p, char * q, std::span<char> s, std::span<char> s2) {
   wprintf(L"hello %s", p); // expected-warning{{function 'wprintf' is unsafe}} expected-note{{string argument is not guaranteed to be null-terminated}}
 
 
-  char a[10], b[11];
+  char a[10];
   int c[10];
+  constexpr unsigned kOneTooBig = 11;
   std::wstring WS;
 
-  snprintf(a, sizeof(b), "%s", __PRETTY_FUNCTION__);         // expected-warning{{function 'snprintf' is unsafe}} expected-note{{buffer pointer and size may not match}}
+  snprintf(a, kOneTooBig, "%s", __PRETTY_FUNCTION__);         // expected-warning{{function 'snprintf' is unsafe}} expected-note{{buffer pointer and size may not match}}
   snprintf((char*)c, sizeof(c), "%s", __PRETTY_FUNCTION__);  // expected-warning{{function 'snprintf' is unsafe}} expected-note{{buffer pointer and size may not match}}
   fprintf((FILE*)p, "%P%d%p%i hello world %32s", *p, *p, p, *p, "hello"); // no warn
   fprintf(fp, "%P%d%p%i hello world %32s", *p, *p, p, *p, "hello"); // no warn

[tsepez]

@shafik @ziqingluo-90 Please take a look.

[ziqingluo-90]

LGTM, but I think we can keep the test of sizeof(b) and add yours at a new line.
Thanks.

[tsepez]

Ok, I believe I have updated the patch in the correct place, please take a look.

[ziqingluo-90]

Thank you @tsepez