[NFC] [C++20] [Modules] Add two tests for comparison lookup within modules

Author: ChuanqiXu9

clang/test/Modules/module-local-hidden-friend.cppm

@@ -0,0 +1,88 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: cd %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/a.cppm -emit-module-interface -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 %t/b.cppm -emit-module-interface -o %t/b.pcm \
+// RUN:     -fmodule-file=a=%t/a.pcm
+// RUN: %clang_cc1 -std=c++20 %t/use.cc -fmodule-file=a=%t/a.pcm -fmodule-file=b=%t/b.pcm \
+// RUN:     -fsyntax-only -verify
+//
+// RUN: %clang_cc1 -std=c++20 %t/a.cppm -emit-reduced-module-interface -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 %t/b.cppm -emit-reduced-module-interface -o %t/b.pcm \
+// RUN:     -fmodule-file=a=%t/a.pcm
+// RUN: %clang_cc1 -std=c++20 %t/use.cc -fmodule-file=a=%t/a.pcm -fmodule-file=b=%t/b.pcm \
+// RUN:     -fsyntax-only -verify
+
+//--- a.cppm
+export module a;
+
+namespace n {
+}
+
+//--- ordering.mock.h
+namespace std {
+  class strong_ordering {
+  public:
+    int n;
+    static const strong_ordering less, equal, greater;
+    constexpr bool operator==(int n) const noexcept { return this->n == n;}
+    constexpr bool operator!=(int n) const noexcept { return this->n != n;}
+  };
+  constexpr strong_ordering strong_ordering::less = {-1};
+  constexpr strong_ordering strong_ordering::equal = {0};
+  constexpr strong_ordering strong_ordering::greater = {1};
+
+  class partial_ordering {
+  public:
+    long n;
+    static const partial_ordering less, equal, greater, equivalent, unordered;
+    constexpr bool operator==(long n) const noexcept { return this->n == n;}
+    constexpr bool operator!=(long n) const noexcept { return this->n != n;}
+  };
+  constexpr partial_ordering partial_ordering::less = {-1};
+  constexpr partial_ordering partial_ordering::equal = {0};
+  constexpr partial_ordering partial_ordering::greater = {1};
+  constexpr partial_ordering partial_ordering::equivalent = {0};
+  constexpr partial_ordering partial_ordering::unordered = {-127};
+} // namespace std
+
+//--- b.cppm
+module;
+#include "ordering.mock.h"
+export module b;
+
+import a;
+
+namespace n {
+
+struct monostate {
+	friend constexpr bool operator==(monostate, monostate) = default;
+};
+
+export struct wrapper {
+	friend constexpr bool operator==(wrapper const &LHS, wrapper const &RHS) {
+        return LHS.m_value == RHS.m_value;
+    }
+
+	monostate m_value;
+};
+
+struct monostate2 {
+	auto operator<=>(monostate2 const &) const & = default;
+};
+
+export struct wrapper2 {
+	friend bool operator==(wrapper2 const &LHS, wrapper2 const &RHS) = default;
+
+	monostate2 m_value;
+};
+
+} // namespace n
+
+//--- use.cc
+// expected-no-diagnostics
+import b;
+
+static_assert(n::wrapper() == n::wrapper());
+static_assert(n::wrapper2() == n::wrapper2());