init

.clang-format

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+BasedOnStyle: "Google"

.clangd

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+CompileFlags:
+  Add: [-std=c++20, -Wextra]

.gitignore

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+.*
+!.clang-format
+!.gitignore
+!.clangd
+build
+tests
+compile_commands.json

README.md

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+# cxx-module-generator
+A tool to easily generate module library from any traditional C++ header library.
+
+It converts a header file like
+```cpp
+// lib.hpp
+namespace A {
+namespace B {
+class C {
+  int a, b;
+};
+}  // namespace B
+}  // namespace A
+```
+into
+```cpp
+// lib.cppm
+module;
+#include "lib.hpp"
+export module test;
+namespace A {
+namespace B {
+export using A::B::C;
+}
+}
+```
+Then you can use `clang++ -march=native -std=c++20 --precompile -c lib.cppm -o lib.pcm` to convert the cppm into pcm.\
+At last, you can use the pcm as a C++20 module:
+```cpp
+import test;
+
+int main() {
+  A::B::C c;
+  return 0;
+}
+```
+By using modules, the build time decreases dramatically.
+
+## Usage
+For example, to convert boost/json.hpp, the module name is boost.json, use `cmg boost/json.hpp --name=boost.json --namespace=boost::json --`. Do not forget the `--` at the end of command. It means ignore any `compile_commands.json` in current directory (which most probably you do not have one). 
+
+Most options are the same as any other clang tools.
+Use `cmg --help` for more help.
+
+Use `find path/in/subtree -name '*.hpp' | xargs cmg --namespace=a::b --` if you need to run on multiple files.
+
+## Install
+**Clang installation is mandatory**
+* Download the file from release section
+* Put it next to clang executable (for msys2, it should be `msys2/clang64/bin`)
+
+## Tested library
+* boost.json

build.cpp

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+#ifdef _WIN32
+#define POSTFIX ".exe"
+#else
+#define POSTFIX ""
+#endif
+
+import std;
+import makeDotCpp;
+import makeDotCpp.project;
+import makeDotCpp.compiler.Clang;
+import makeDotCpp.fileProvider.Glob;
+import makeDotCpp.builder;
+
+#include "project.json.hpp"
+
+using namespace makeDotCpp;
+
+int main(int argc, const char **argv) {
+  std::deque<std::shared_ptr<Export>> packages;
+  populatePackages(packages);
+
+  Project::OptionParser op;
+  op.parse(argc, argv);
+
+  auto compiler = std::make_shared<Clang>();
+  compiler->addOption("-march=native -std=c++20 -O3 -Wall")
+      .addLinkOption("-lclang-cpp")
+      .addLinkOption("-lLLVM-18")
+      .addLinkOption("-Wl,--stack=4194304");
+
+  ExeBuilder builder("cmg");
+  builder.setCompiler(compiler)
+      .addSrc(Glob("src/**/*.cppm"))
+      .addSrc("src/main.cpp");
+
+  for (auto &package : packages) {
+    builder.dependOn(package);
+  }
+
+  Project()
+      .setName("cxx-module-generator")
+      .setBuild([&](const Context &ctx) {
+        auto future = builder.build(ctx);
+        future.get();
+        std::cout << "\033[0;32mDone\033[0m" << std::endl;
+      })
+      .setInstall([](const Context &) {})
+      .run(op);
+}

project.json

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+{
+  "name": "cxx-module-generator",
+  "dev": {
+    "packages": [
+      "makeDotCpp"
+    ]
+  }
+}

src/main.cpp

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+#include <clang/AST/Decl.h>
+#include <clang/AST/RecursiveASTVisitor.h>
+#include <clang/AST/Type.h>
+#include <clang/Frontend/CompilerInstance.h>
+#include <clang/Tooling/CommonOptionsParser.h>
+#include <clang/Tooling/Tooling.h>
+#include <llvm/Support/raw_ostream.h>
+
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+
+using namespace clang;
+using namespace tooling;
+namespace fs = std::filesystem;
+
+static llvm::cl::OptionCategory toolCategory("cxx-module-generator");
+static llvm::cl::opt<std::string> moduleName("name",
+                                             llvm::cl::desc("Module name"),
+                                             llvm::cl::cat(toolCategory));
+static llvm::cl::opt<std::string> output("o",
+                                         llvm::cl::desc("Specify output path"),
+                                         llvm::cl::cat(toolCategory));
+static llvm::cl::opt<std::string> nsFilter(
+    "namespace", llvm::cl::desc("Filter symbol by namespace"),
+    llvm::cl::cat(toolCategory));
+
+class ModuleWrapper {
+ private:
+  std::string content;
+
+ public:
+  ModuleWrapper(const fs::path &originalFile) {
+    content += "module;\n#include \"" + originalFile.generic_string() + "\"\n";
+    content += "export module " +
+               (!moduleName.empty() ? moduleName.getValue()
+                                    : originalFile.stem().string()) +
+               ";\n";
+  }
+
+  void openNamespace(NamespaceDecl *decl) {
+    content += "namespace " + decl->getNameAsString() + " {\n";
+  }
+
+  void closeNamespace(NamespaceDecl *) { content += "}\n"; }
+
+  void addSymbol(NamedDecl *decl) {
+    if (decl != nullptr && decl->isFirstDecl())
+      content += "export using " + decl->getQualifiedNameAsString() + ";\n";
+  }
+
+  const std::string &getContent() const { return content; }
+};
+
+class FindAllSymbols : public RecursiveASTVisitor<FindAllSymbols> {
+ private:
+  using Base = RecursiveASTVisitor<FindAllSymbols>;
+
+  ModuleWrapper &wrapper;
+
+ public:
+  FindAllSymbols(ModuleWrapper &wrapper) : wrapper(wrapper) {}
+
+  bool TraverseNamespaceDecl(NamespaceDecl *decl) {
+    if (nsFilter.find(decl->getName()) != std::string::npos) {
+      wrapper.openNamespace(decl);
+      Base::TraverseNamespaceDecl(decl);
+      wrapper.closeNamespace(decl);
+    }
+    return true;
+  }
+
+  bool TraverseDecl(Decl *decl) {
+    switch (decl->getKind()) {
+      case Decl::TranslationUnit:
+        return TraverseTranslationUnitDecl(
+            static_cast<TranslationUnitDecl *>(decl));
+      case Decl::Namespace:
+        return TraverseNamespaceDecl(static_cast<NamespaceDecl *>(decl));
+      default:
+        break;
+    }
+    switch (decl->getKind()) {
+#define ABSTRACT_DECL(DECL)
+#define DECL(CLASS, BASE)                                           \
+  case Decl::CLASS:                                                 \
+    if (!WalkUpFrom##CLASS##Decl(static_cast<CLASS##Decl *>(decl))) \
+      return false;                                                 \
+    break;
+#include "clang/AST/DeclNodes.inc"
+    }
+    return true;
+  }
+
+#define VISIT_DECL(TYPE)                                                      \
+  bool Visit##TYPE##Decl(TYPE##Decl *decl) {                                  \
+    if (!decl->isImplicit() &&                                                \
+        decl->getQualifiedNameAsString().find(nsFilter) != std::string::npos) \
+      wrapper.addSymbol(decl);                                                \
+    return true;                                                              \
+  }
+
+  VISIT_DECL(Tag);
+  VISIT_DECL(TypedefName);
+  VISIT_DECL(Function);
+#undef VISIT_DECL
+};
+
+class CreateModule : public ASTConsumer {
+ private:
+  fs::path path;
+
+ public:
+  CreateModule(const fs::path &path) : path(fs::canonical(path)) {}
+
+  void HandleTranslationUnit(ASTContext &ctx) override {
+    ModuleWrapper wrapper(path);
+    FindAllSymbols visitor(wrapper);
+    visitor.TraverseDecl(ctx.getTranslationUnitDecl());
+    auto modulePath = output.getValue() / path.stem() += ".cppm";
+    fs::create_directories(modulePath.parent_path());
+    std::ofstream os{modulePath, std::ios::binary};
+    os.exceptions(std::ios::failbit);
+    os << wrapper.getContent();
+  }
+};
+
+template <class Consumer>
+class SuppressIncludeNotFound : public ASTFrontendAction {
+ public:
+  std::unique_ptr<ASTConsumer> CreateASTConsumer(
+      CompilerInstance &, llvm::StringRef path) override {
+    return std::make_unique<Consumer>(path.str());
+  }
+};
+
+int main(int argc, const char **argv) {
+  output.setInitialValue(fs::current_path().generic_string());
+  auto expectedParser = CommonOptionsParser::create(argc, argv, toolCategory);
+  if (!expectedParser) {
+    llvm::errs() << expectedParser.takeError();
+    return 1;
+  }
+  CommonOptionsParser &op = expectedParser.get();
+  ClangTool tool(op.getCompilations(), op.getSourcePathList());
+  return tool.run(
+      newFrontendActionFactory<SuppressIncludeNotFound<CreateModule>>().get());
+}