| ========================================================== |
| How to write RecursiveASTVisitor based ASTFrontendActions. |
| ========================================================== |
| |
| Introduction |
| ============ |
| |
| In this tutorial you will learn how to create a FrontendAction that uses |
| a RecursiveASTVisitor to find CXXRecordDecl AST nodes with a specified |
| name. |
| |
| Creating a FrontendAction |
| ========================= |
| |
| When writing a clang based tool like a Clang Plugin or a standalone tool |
| based on LibTooling, the common entry point is the FrontendAction. |
| FrontendAction is an interface that allows execution of user specific |
| actions as part of the compilation. To run tools over the AST clang |
| provides the convenience interface ASTFrontendAction, which takes care |
| of executing the action. The only part left is to implement the |
| CreateASTConsumer method that returns an ASTConsumer per translation |
| unit. |
| |
| :: |
| |
| class FindNamedClassAction : public clang::ASTFrontendAction { |
| public: |
| virtual std::unique_ptr<clang::ASTConsumer> CreateASTConsumer( |
| clang::CompilerInstance &Compiler, llvm::StringRef InFile) { |
| return std::unique_ptr<clang::ASTConsumer>( |
| new FindNamedClassConsumer); |
| } |
| }; |
| |
| Creating an ASTConsumer |
| ======================= |
| |
| ASTConsumer is an interface used to write generic actions on an AST, |
| regardless of how the AST was produced. ASTConsumer provides many |
| different entry points, but for our use case the only one needed is |
| HandleTranslationUnit, which is called with the ASTContext for the |
| translation unit. |
| |
| :: |
| |
| class FindNamedClassConsumer : public clang::ASTConsumer { |
| public: |
| virtual void HandleTranslationUnit(clang::ASTContext &Context) { |
| // Traversing the translation unit decl via a RecursiveASTVisitor |
| // will visit all nodes in the AST. |
| Visitor.TraverseDecl(Context.getTranslationUnitDecl()); |
| } |
| private: |
| // A RecursiveASTVisitor implementation. |
| FindNamedClassVisitor Visitor; |
| }; |
| |
| Using the RecursiveASTVisitor |
| ============================= |
| |
| Now that everything is hooked up, the next step is to implement a |
| RecursiveASTVisitor to extract the relevant information from the AST. |
| |
| The RecursiveASTVisitor provides hooks of the form bool |
| VisitNodeType(NodeType \*) for most AST nodes; the exception are TypeLoc |
| nodes, which are passed by-value. We only need to implement the methods |
| for the relevant node types. |
| |
| Let's start by writing a RecursiveASTVisitor that visits all |
| CXXRecordDecl's. |
| |
| :: |
| |
| class FindNamedClassVisitor |
| : public RecursiveASTVisitor<FindNamedClassVisitor> { |
| public: |
| bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| // For debugging, dumping the AST nodes will show which nodes are already |
| // being visited. |
| Declaration->dump(); |
| |
| // The return value indicates whether we want the visitation to proceed. |
| // Return false to stop the traversal of the AST. |
| return true; |
| } |
| }; |
| |
| In the methods of our RecursiveASTVisitor we can now use the full power |
| of the Clang AST to drill through to the parts that are interesting for |
| us. For example, to find all class declaration with a certain name, we |
| can check for a specific qualified name: |
| |
| :: |
| |
| bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| if (Declaration->getQualifiedNameAsString() == "n::m::C") |
| Declaration->dump(); |
| return true; |
| } |
| |
| Accessing the SourceManager and ASTContext |
| ========================================== |
| |
| Some of the information about the AST, like source locations and global |
| identifier information, are not stored in the AST nodes themselves, but |
| in the ASTContext and its associated source manager. To retrieve them we |
| need to hand the ASTContext into our RecursiveASTVisitor implementation. |
| |
| The ASTContext is available from the CompilerInstance during the call to |
| CreateASTConsumer. We can thus extract it there and hand it into our |
| freshly created FindNamedClassConsumer: |
| |
| :: |
| |
| virtual std::unique_ptr<clang::ASTConsumer> CreateASTConsumer( |
| clang::CompilerInstance &Compiler, llvm::StringRef InFile) { |
| return std::unique_ptr<clang::ASTConsumer>( |
| new FindNamedClassConsumer(&Compiler.getASTContext())); |
| } |
| |
| Now that the ASTContext is available in the RecursiveASTVisitor, we can |
| do more interesting things with AST nodes, like looking up their source |
| locations: |
| |
| :: |
| |
| bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| if (Declaration->getQualifiedNameAsString() == "n::m::C") { |
| // getFullLoc uses the ASTContext's SourceManager to resolve the source |
| // location and break it up into its line and column parts. |
| FullSourceLoc FullLocation = Context->getFullLoc(Declaration->getBeginLoc()); |
| if (FullLocation.isValid()) |
| llvm::outs() << "Found declaration at " |
| << FullLocation.getSpellingLineNumber() << ":" |
| << FullLocation.getSpellingColumnNumber() << "\n"; |
| } |
| return true; |
| } |
| |
| Putting it all together |
| ======================= |
| |
| Now we can combine all of the above into a small example program: |
| |
| :: |
| |
| #include "clang/AST/ASTConsumer.h" |
| #include "clang/AST/RecursiveASTVisitor.h" |
| #include "clang/Frontend/CompilerInstance.h" |
| #include "clang/Frontend/FrontendAction.h" |
| #include "clang/Tooling/Tooling.h" |
| |
| using namespace clang; |
| |
| class FindNamedClassVisitor |
| : public RecursiveASTVisitor<FindNamedClassVisitor> { |
| public: |
| explicit FindNamedClassVisitor(ASTContext *Context) |
| : Context(Context) {} |
| |
| bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| if (Declaration->getQualifiedNameAsString() == "n::m::C") { |
| FullSourceLoc FullLocation = Context->getFullLoc(Declaration->getBeginLoc()); |
| if (FullLocation.isValid()) |
| llvm::outs() << "Found declaration at " |
| << FullLocation.getSpellingLineNumber() << ":" |
| << FullLocation.getSpellingColumnNumber() << "\n"; |
| } |
| return true; |
| } |
| |
| private: |
| ASTContext *Context; |
| }; |
| |
| class FindNamedClassConsumer : public clang::ASTConsumer { |
| public: |
| explicit FindNamedClassConsumer(ASTContext *Context) |
| : Visitor(Context) {} |
| |
| virtual void HandleTranslationUnit(clang::ASTContext &Context) { |
| Visitor.TraverseDecl(Context.getTranslationUnitDecl()); |
| } |
| private: |
| FindNamedClassVisitor Visitor; |
| }; |
| |
| class FindNamedClassAction : public clang::ASTFrontendAction { |
| public: |
| virtual std::unique_ptr<clang::ASTConsumer> CreateASTConsumer( |
| clang::CompilerInstance &Compiler, llvm::StringRef InFile) { |
| return std::unique_ptr<clang::ASTConsumer>( |
| new FindNamedClassConsumer(&Compiler.getASTContext())); |
| } |
| }; |
| |
| int main(int argc, char **argv) { |
| if (argc > 1) { |
| clang::tooling::runToolOnCode(std::make_unique<FindNamedClassAction>(), argv[1]); |
| } |
| } |
| |
| We store this into a file called FindClassDecls.cpp and create the |
| following CMakeLists.txt to link it: |
| |
| :: |
| |
| add_clang_executable(find-class-decls FindClassDecls.cpp) |
| |
| target_link_libraries(find-class-decls clangTooling) |
| |
| When running this tool over a small code snippet it will output all |
| declarations of a class n::m::C it found: |
| |
| :: |
| |
| $ ./bin/find-class-decls "namespace n { namespace m { class C {}; } }" |
| Found declaration at 1:29 |
| |