[parsing] Drop compatibility code for Ventura (#22029)

Author: rpoyner-tri

Diff for: multibody/parsing/detail_instanced_name.cc

@@ -6,28 +6,6 @@ namespace drake {
 namespace multibody {
 namespace internal {
 
-// Apple Xcode fails to correctly implement <=> for either
-// std::optional (prior to 15.3) or std::string (prior to 15.2
-// maybe?), so the default implementation of <=> here gets
-// "implicitly deleted", leading to a train of compile errors. So,
-// until Ventura support ends, write an explicit implementation
-// instead.
-//
-// TODO(rpoyner-tri): replace explicit implementation with compiler
-// default once macOS Ventura support ends.
-std::strong_ordering InstancedName::operator<=>(
-    const InstancedName& that) const {
-  if (index.has_value() && that.index.has_value()) {
-    if (auto cmp = (*index <=> *that.index); cmp != 0) {
-      return cmp;
-    }
-  }
-  if (auto cmp = (index.has_value() <=> that.index.has_value()); cmp != 0) {
-    return cmp;
-  }
-  return std::strcmp(name.c_str(), that.name.c_str()) <=> 0;
-}
-
 std::string InstancedName::to_string() const {
   return fmt::format(
       "[{}, {}]", index.has_value() ? fmt::to_string(*index) : "nullopt", name);

Diff for: multibody/parsing/detail_instanced_name.h

@@ -19,9 +19,7 @@ struct InstancedName {
   std::string name;
 
   bool operator==(const InstancedName&) const = default;
-  // TODO(rpoyner-tri): replace explicit implementation with compiler
-  // default once macOS Ventura support ends.
-  std::strong_ordering operator<=>(const InstancedName& that) const;
+  auto operator<=>(const InstancedName& that) const = default;
 
   std::string to_string() const;
 };

Diff for: multibody/parsing/test/detail_instanced_name_test.cc

@@ -8,29 +8,6 @@ namespace multibody {
 namespace internal {
 namespace {
 
-// TODO(rpoyner-tri): replace explicit spaceship implementation with compiler
-// default once macOS Ventura support ends. Once it is gone, this test (and
-// perhaps this whole file) can go too.
-GTEST_TEST(InstancedNameTest, ExplicitSpaceship) {
-  InstancedName empty;
-  InstancedName global_a{{}, "a"};
-  InstancedName global_b{{}, "b"};
-  InstancedName one_a{ModelInstanceIndex(1), "a"};
-  InstancedName one_b{ModelInstanceIndex(1), "b"};
-  InstancedName two_a{ModelInstanceIndex(2), "a"};
-  InstancedName two_b{ModelInstanceIndex(2), "b"};
-
-  std::vector ordered{
-    empty, global_a, global_b, one_a, one_b, two_a, two_b};
-
-  for (int ii = 0; ii < ssize(ordered); ++ii) {
-    for (int jj = 0; jj < ssize(ordered); ++jj) {
-      SCOPED_TRACE(fmt::format("compare at ({}, {})", ii, jj));
-      EXPECT_EQ(ordered[ii] <=> ordered[jj], ii <=> jj);
-    }
-  }
-}
-
 GTEST_TEST(InstanceNameTest, ToString) {
   InstancedName empty;
   EXPECT_EQ(empty.to_string(), "[nullopt, ]");