Add "-M" and "-MM" command line options to dump the dependencies of t…

src/frontend/cxx/cli.cc

@@ -132,6 +132,12 @@ std::vector<CLIOptionDescr> options{
     {"-dM", "Print macro definitions in -E mode instead of normal output",
      &CLI::opt_dM},
 
+    {"-M", "Print dependencies of the main source file",
+     &CLI::opt_M},
+
+    {"-MM", "Print dependencies of the main source file, excluding system path",
+     &CLI::opt_MM},
+
     {"-S", "Only run preprocess and compilation steps", &CLI::opt_S,
      CLIOptionVisibility::kExperimental},
 

src/frontend/cxx/cli.h

@@ -54,6 +54,8 @@ class CLI {
   bool opt_ast_dump = false;
   bool opt_ir_dump = false;
   bool opt_dM = false;
+  bool opt_MM = false;
+  bool opt_M = false;
   bool opt_dump_symbols = false;
   bool opt_dump_tokens = false;
   bool opt_E = false;

src/frontend/cxx/frontend.cc

@@ -238,7 +238,7 @@ auto runOnFile(const CLI& cli, const std::string& fileName) -> bool {
   }
 
   if (auto source = readAll(fileName)) {
-    if (cli.opt_E && !cli.opt_dM) {
+    if (cli.opt_E && !(cli.opt_dM || cli.opt_M || cli.opt_MM)) {
       preprocesor->preprocess(std::move(*source), fileName, output);
       shouldExit = true;
     } else {
@@ -247,6 +247,12 @@ auto runOnFile(const CLI& cli, const std::string& fileName) -> bool {
       if (cli.opt_dM) {
         preprocesor->printMacros(output);
         shouldExit = true;
+      } else if (cli.opt_M) {
+        preprocesor->printDependencies(output, false);
+        shouldExit = true;
+      } else if (cli.opt_MM) {
+        preprocesor->printDependencies(output, true);
+        shouldExit = true;
       } else if (cli.opt_dump_tokens) {
         dumpTokens(cli, unit, output);
         shouldExit = true;

src/parser/cxx/preprocessor.cc

@@ -2262,6 +2262,27 @@ void Preprocessor::printMacros(std::ostream &out) const {
   }
 }
 
+void Preprocessor::printDependencies(std::ostream &out, bool noSysPath) const {
+  if (d->sourceFiles_.size() == 0) return;
+  const auto p = fs::path(d->sourceFiles_[0]->fileName);
+  const std::string stem = p.stem();
+  out << cxx::format("{}.o:", stem);
+  for (const auto &sourceFile : d->sourceFiles_) {
+    if (noSysPath) {
+      bool isSysPath = false;
+      for (const auto &sysPath : d->systemIncludePaths_) {
+        if (sourceFile->fileName.find(sysPath) == 0) {
+          isSysPath = true;
+          break;
+        }
+      }
+      if (isSysPath) continue;
+    }
+    out << cxx::format(" \\\n  {}", sourceFile->fileName);
+  }
+  out << "\n";
+}
+
 void Preprocessor::getTokenStartPosition(const Token &token, unsigned *line,
                                          unsigned *column,
                                          std::string_view *fileName) const {

src/parser/cxx/preprocessor.h

@@ -97,6 +97,8 @@ class Preprocessor {
 
   void printMacros(std::ostream &out) const;
 
+  void printDependencies(std::ostream &out, bool noSysPath) const;
+
   void getTokenStartPosition(const Token &token, unsigned *line,
                              unsigned *column,
                              std::string_view *fileName) const;