[libcxx-commits] [libcxx] [libcxx] Handle windows system error code mapping in std::error_code. (PR #93101)

[James Y Knight via libcxx-commits]

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@@ -156,19 +229,52 @@ class _LIBCPP_HIDDEN __system_error_category : public __do_message {
 const char* __system_error_category::name() const noexcept { return "system"; }
 
 string __system_error_category::message(int ev) const {
-#ifdef _LIBCPP_ELAST
+#ifdef _LIBCPP_WIN32API
+  std::string result;
+  char* str               = nullptr;
+  unsigned long num_chars = FormatMessageA(
+      FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
+      nullptr,
+      ev,
+      0,
+      reinterpret_cast<char*>(&str),
+      0,
+      nullptr);
+  auto is_whitespace = [](char ch) { return ch == '\n' || ch == '\r' || ch == ' '; };
+  while (num_chars > 0 && is_whitespace(str[num_chars - 1]))
+    --num_chars;
+
+  if (num_chars)
+    result = std::string(str, num_chars);
+  else
+    result = "Unknown error";
+
+  LocalFree(str);
+  return result;
+#else
+#  ifdef _LIBCPP_ELAST
   if (ev > _LIBCPP_ELAST)
     return string("unspecified system_category error");
-#endif // _LIBCPP_ELAST
+#  endif // _LIBCPP_ELAST
   return __do_message::message(ev);
+#endif
 }
 
 error_condition __system_error_category::default_error_condition(int ev) const noexcept {
-#ifdef _LIBCPP_ELAST
+#ifdef _LIBCPP_WIN32API
+  // Remap windows error codes to generic error codes if possible.
+  if (ev == 0)
+    return error_condition(0, generic_category());
+  if (auto maybe_errc = __win_err_to_errc(ev))
+    return error_condition(static_cast<int>(maybe_errc.value()), generic_category());
----------------
jyknight wrote:

Done.

https://github.com/llvm/llvm-project/pull/93101