[libc-commits] [libc] [libc] Add `ctime_s` (PR #110676)

[Nick Desaulniers via libc-commits]

================
@@ -37,6 +37,14 @@ functions:
     arguments:
       - type: const time_t *
       - type: char *
+  - name: ctime_s
+    standard:
+      - stdc
+    return_type: errno_t
+    arguments:
+      - type: char *
+      - type: rsize_t
+      - type: const time_t *
----------------
nickdesaulniers wrote:

Ok, so the last thing I think we should resolve before landing this is related to this problem, so "unresolving the conversation."

When you build llvm-libc in fullbuild mode, we generate `{build_dir}/build/libc/include/time.h`. It has:
```c
#ifdef __STDC_WANT_LIB_EXT1__                                                                                    
errno_t ctime_s(char *, rsize_t, const time_t *) __NOEXCEPT;                    
#endif // __STDC_WANT_LIB_EXT1__
```
Looks good, yeah? But one issue I think will be when someone does:
```c
#define __STDC_WANT_LIB_EXT1__ 1
#include <time.h>
```
then they'll get some error that `errno_t` is undefined.  So I think you'll need the manual inclusion of `errno.h` in libc/include/time.h.def.  I guess we can make it conditional on `__STDC_WANT_LIB_EXT1__` as well.

```diff
diff --git a/libc/include/time.h.def b/libc/include/time.h.def
index 2355e8822fad..c745a4317504 100644
--- a/libc/include/time.h.def
+++ b/libc/include/time.h.def
@@ -12,6 +12,10 @@
 #include "__llvm-libc-common.h"
 #include "llvm-libc-macros/time-macros.h"
 
+#ifdef __STDC_WANT_LIB_EXT1__
+#include <errno.h> // errno_t
+#endif
+
 %%public_api()
 
 #endif // LLVM_LIBC_TIME_H
```
mind adding that to your PR?

https://github.com/llvm/llvm-project/pull/110676