[llvm-branch-commits] [libcxx] [libc++][chrono] Fixes leap seconds. (PR #90070)

[Louis Dionne via llvm-branch-commits]

================
@@ -626,29 +626,49 @@ static void __parse_leap_seconds(vector<leap_second>& __leap_seconds, istream&&
   // seconds since 1 January 1970.
   constexpr auto __offset = sys_days{1970y / January / 1} - sys_days{1900y / January / 1};
 
-  while (true) {
-    switch (__input.peek()) {
-    case istream::traits_type::eof():
-      return;
-
-    case ' ':
-    case '\t':
-    case '\n':
-      __input.get();
-      continue;
+  struct __entry {
+    sys_seconds __timestamp;
+    seconds __value;
+  };
+  vector<__entry> __entries;
+  [&] {
+    while (true) {
+      switch (__input.peek()) {
+      case istream::traits_type::eof():
+        return;
+
+      case ' ':
+      case '\t':
+      case '\n':
+        __input.get();
+        continue;
+
+      case '#':
+        chrono::__skip_line(__input);
+        continue;
+      }
 
-    case '#':
+      sys_seconds __date = sys_seconds{seconds{chrono::__parse_integral(__input, false)}} - __offset;
+      chrono::__skip_mandatory_whitespace(__input);
+      seconds __value{chrono::__parse_integral(__input, false)};
       chrono::__skip_line(__input);
-      continue;
-    }
 
-    sys_seconds __date = sys_seconds{seconds{chrono::__parse_integral(__input, false)}} - __offset;
-    chrono::__skip_mandatory_whitespace(__input);
-    seconds __value{chrono::__parse_integral(__input, false)};
-    chrono::__skip_line(__input);
-
-    __leap_seconds.emplace_back(std::__private_constructor_tag{}, __date, __value);
-  }
+      __entries.emplace_back(__date, __value);
+    }
+  }();
+  // The Standard requires the leap seconds to be sorted. The file
+  // leap-seconds.list usually provides them in sorted order, but that is not
+  // guaranteed so we ensure it here.
+  std::ranges::sort(__entries, {}, &__entry::__timestamp);
+
+  // The database should contain the number of seconds inserted by a leap
+  // second (1 or -1). So the difference between the two elements are stored.
----------------
ldionne wrote:

```suggestion
  // second (1 or -1). So the difference between the two elements is stored.
```

https://github.com/llvm/llvm-project/pull/90070