[c++20] Improve phrasing of diagnostic for missing #include <compare>.
diff --git a/clang/test/SemaCXX/std-compare-cxx2a.cpp b/clang/test/SemaCXX/std-compare-cxx2a.cpp
index 941c4fa..3febb8f 100644
--- a/clang/test/SemaCXX/std-compare-cxx2a.cpp
+++ b/clang/test/SemaCXX/std-compare-cxx2a.cpp
@@ -3,10 +3,24 @@
 // RUN: %clang_cc1 -triple x86_64-apple-darwin -fcxx-exceptions -fsyntax-only -pedantic -verify -Wsign-compare -std=c++2a %s
 
 void compare_not_found_test() {
-  // expected-error@+1 {{cannot deduce return type of 'operator<=>' because type 'std::partial_ordering' was not found; include <compare>}}
+  // expected-error@+1 {{cannot use builtin operator '<=>' because type 'std::partial_ordering' was not found; include <compare>}}
   (void)(0.0 <=> 42.123);
 }
 
+struct deduction_compare_not_found {
+  // expected-error@+1 {{cannot default 'operator<=>' because type 'std::strong_ordering' was not found; include <compare>}}
+  friend auto operator<=>(const deduction_compare_not_found&, const deduction_compare_not_found&) = default;
+};
+
+struct comparable {
+  int operator<=>(comparable);
+};
+struct default_compare_not_found {
+  // expected-error@+1 {{cannot default 'operator<=>' because type 'std::strong_ordering' was not found; include <compare>}}
+  friend int operator<=>(const default_compare_not_found&, const default_compare_not_found&) = default;
+};
+bool b = default_compare_not_found() < default_compare_not_found(); // expected-note {{first required here}}
+
 namespace std {
 inline namespace __1 {
 struct partial_ordering; // expected-note {{forward declaration}}