[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:

For the build failure, the issue is in a file you did not touch directly, `libc/src/time/asctime_r.cpp`. It includes `libc/src/time/asctime_r.h`, which includes `time.h` which is dynamically built at build time of llvm-libc since this is a "full build" (`-DLLVM_LIBC_FULL_BUILD=ON` is set in the buildbot's cmake invocation as seen in the logs).

The issue is that now anyone who includes the generated time.h will see a declaration of `ctime_s` and its return type of `errno_t` and its parameter of type `rsize_t` EVEN when they did not first `#define __STDC_WANT_LIB_EXT1__ 1`.  IIRC, we added a field for hdrgen called `guard` which should wrap the declaration in a preprocessor guard.

So to fix the presubmit build failure, I think you just need to add:

```suggestion
      - type: const time_t *
    guard: __STDC_WANT_LIB_EXT1__
```

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