Use typeid() only if it's available

On MSVC it is always available, otherwise it depends on whether RTTI is enabled.
fmtlib · May 31, 2023 · 9aa817d · 9aa817d
1 parent bd39345
commit 9aa817d
Showing 1 changed file with 25 additions and 5 deletions.
diff --git a/include/fmt/std.h b/include/fmt/std.h
@@ -44,6 +44,24 @@
 #  endif
 #endif
 
+// Check if typeid is available.
+#ifndef FMT_USE_TYPEID
+// In MSVC, typeid() is available with or without RTTI.
+#  if defined(_MSC_VER)
+#    define FMT_USE_TYPEID 1
+#  elif defined(__RTTI)  // EDG compilers.
+#    define FMT_USE_TYPEID 1
+#  elif defined(__INTEL_RTTI__)  // Intel compiler.
+#    define FMT_USE_TYPEID 1
+#  elif defined(__GXX_RTTI)  // G++.
+#    define FMT_USE_TYPEID 1
+#  elif FMT_HAS_FEATURE(cxx_rtti)  // Clang.
+#    define FMT_USE_TYPEID 1
+#  else
+#    define FMT_USE_TYPEID 0
+#  endif
+#endif
+
 #ifdef __cpp_lib_filesystem
 FMT_BEGIN_NAMESPACE
 
@@ -274,7 +292,7 @@ struct formatter<
     if (it == end || *it == '}') return it;
     if (*it == 't') {
       ++it;
-      with_typename_ = true;
+      with_typename_ = FMT_USE_TYPEID != 0;
     }
     return it;
   }
@@ -287,8 +305,9 @@ struct formatter<
     if (!with_typename_)
       return detail::write_bytes(out, string_view(ex.what()), spec);
 
+#if FMT_USE_TYPEID
     const std::type_info& ti = typeid(ex);
-#ifdef FMT_HAS_ABI_CXA_DEMANGLE
+#  ifdef FMT_HAS_ABI_CXA_DEMANGLE
     int status = 0;
     std::size_t size = 0;
     std::unique_ptr<char, decltype(&std::free)> demangled_name_ptr(
@@ -327,21 +346,22 @@ struct formatter<
       demangled_name_view = string_view(ti.name());
     }
     out = detail::write_bytes(out, demangled_name_view, spec);
-#elif FMT_MSC_VERSION
+#  elif FMT_MSC_VERSION
     string_view demangled_name_view(ti.name());
     if (demangled_name_view.starts_with("class "))
       demangled_name_view.remove_prefix(6);
     else if (demangled_name_view.starts_with("struct "))
       demangled_name_view.remove_prefix(7);
     out = detail::write_bytes(out, demangled_name_view, spec);
-#else
+#  else
     out = detail::write_bytes(out, string_view(ti.name()), spec);
-#endif
+#  endif
     out = detail::write<Char>(out, Char(':'));
     out = detail::write<Char>(out, Char(' '));
     out = detail::write_bytes(out, string_view(ex.what()), spec);
 
     return out;
+#endif
   }
 };
 FMT_END_NAMESPACE