[C++20] [Modules] Emit Macro Definition in -module-file-info action

It is helpful to know whih macro definition is emitted in the module
file without openning it directly. And this is not easy to be tested
with the lit test. So this patch add the facility to emit macro
definitions in `-module-file-info` action. And this should be innnocent
for every other cases.

Author: ChuanqiXu9

clang/lib/Frontend/FrontendActions.cpp

@@ -938,6 +938,20 @@ void DumpModuleInfoAction::ExecuteAction() {
         }
       }
     }
+
+    // Emit the macro definitions in the module file so that we can know how
+    // much definitions in the module file quickly.
+    // TODO: Emit the macro definition bodies completely.
+    if (auto FilteredMacros = llvm::make_filter_range(
+            R->getPreprocessor().macros(),
+            [](const auto &Macro) { return Macro.first->isFromAST(); });
+        !FilteredMacros.empty()) {
+      Out << "   Macro Definitions:\n";
+      for (/*<IdentifierInfo *, MacroState> pair*/ const auto &Macro :
+           FilteredMacros)
+        Out << "     " << Macro.first->getName() << "\n";
+    }
+
     // Now let's print out any modules we did not see as part of the Primary.
     for (auto SM : SubModMap) {
       if (!SM.second.Seen && SM.second.Mod) {

clang/test/Modules/cxx20-module-file-info-macros.cpp

@@ -0,0 +1,74 @@
+// Test the output from -module-file-info about C++20 Modules
+// can reflect macros definitions correctly.
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header %t/foo.h -o %t/foo.pcm
+// RUN: %clang_cc1 -module-file-info %t/foo.pcm | FileCheck %t/foo.h
+//
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header %t/include_foo.h -o %t/include_foo.pcm
+// RUN: %clang_cc1 -module-file-info %t/include_foo.pcm | FileCheck %t/include_foo.h
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header -fmodule-file=%t/foo.pcm \
+// RUN:     %t/import_foo.h -o %t/import_foo.pcm
+// RUN: %clang_cc1 -module-file-info %t/import_foo.pcm | FileCheck %t/import_foo.h
+//
+// RUN: %clang_cc1 -std=c++20 %t/named_module.cppm -emit-module-interface -o %t/M.pcm
+// RUN: %clang_cc1 -module-file-info %t/M.pcm | FileCheck %t/named_module.cppm
+
+//--- foo.h
+#pragma once
+#define FOO
+#define CONSTANT 43
+#define FUNC_Macro(X) (X+1)
+#define TO_BE_UNDEF
+#undef TO_BE_UNDEF
+
+#ifndef FOO
+#define CONDITIONAL_DEF
+#endif
+
+#define REDEFINE
+#define REDEFINE
+
+// CHECK: Macro Definitions:
+// CHECK-DAG: REDEFINE
+// CHECK-DAG: FUNC_Macro
+// CHECK-DAG: CONSTANT
+// CHECK-DAG: FOO
+// CHECK-NEXT: ===
+
+//--- include_foo.h
+#include "foo.h"
+#undef REDEFINE
+// CHECK: Macro Definitions:
+// CHECK-DAG: CONSTANT
+// CHECK-DAG: FUNC_Macro
+// CHECK-DAG: FOO
+// CHECK-NEXT: ===
+
+//--- import_foo.h
+import "foo.h";
+#undef REDEFINE
+// CHECK: Macro Definitions:
+// CHECK-DAG: CONSTANT
+// CHECK-DAG: FUNC_Macro
+// CHECK-DAG: FOO
+// CHECK-NEXT: ===
+
+//--- named_module.cppm
+module;
+#include "foo.h"
+export module M;
+#define M_Module 43
+// FIXME: It is meaningless for named modules to emit macro definitions.
+// It wastes the time and spaces completely.
+// CHECK: Macro Definitions:
+// CHECK-DAG: M_Module
+// CHECK-DAG: REDEFINE
+// CHECK-DAG: FUNC_Macro
+// CHECK-DAG: TO_BE_UNDEF
+// CHECK-DAG: FOO
+// CHECK-DAG: CONSTANT
+// CHECK-NEXT: ===