Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 1 | ========================================================== |
| 2 | How to write RecursiveASTVisitor based ASTFrontendActions. |
| 3 | ========================================================== |
| 4 | |
| 5 | Introduction |
| 6 | ============ |
| 7 | |
| 8 | In this tutorial you will learn how to create a FrontendAction that uses |
| 9 | a RecursiveASTVisitor to find CXXRecordDecl AST nodes with a specified |
| 10 | name. |
| 11 | |
| 12 | Creating a FrontendAction |
| 13 | ========================= |
| 14 | |
| 15 | When writing a clang based tool like a Clang Plugin or a standalone tool |
| 16 | based on LibTooling, the common entry point is the FrontendAction. |
| 17 | FrontendAction is an interface that allows execution of user specific |
| 18 | actions as part of the compilation. To run tools over the AST clang |
| 19 | provides the convenience interface ASTFrontendAction, which takes care |
| 20 | of executing the action. The only part left is to implement the |
| 21 | CreateASTConsumer method that returns an ASTConsumer per translation |
| 22 | unit. |
| 23 | |
| 24 | :: |
| 25 | |
| 26 | class FindNamedClassAction : public clang::ASTFrontendAction { |
| 27 | public: |
| 28 | virtual clang::ASTConsumer *CreateASTConsumer( |
| 29 | clang::CompilerInstance &Compiler, llvm::StringRef InFile) { |
| 30 | return new FindNamedClassConsumer; |
| 31 | } |
| 32 | }; |
| 33 | |
| 34 | Creating an ASTConsumer |
| 35 | ======================= |
| 36 | |
| 37 | ASTConsumer is an interface used to write generic actions on an AST, |
| 38 | regardless of how the AST was produced. ASTConsumer provides many |
| 39 | different entry points, but for our use case the only one needed is |
| 40 | HandleTranslationUnit, which is called with the ASTContext for the |
| 41 | translation unit. |
| 42 | |
| 43 | :: |
| 44 | |
| 45 | class FindNamedClassConsumer : public clang::ASTConsumer { |
| 46 | public: |
| 47 | virtual void HandleTranslationUnit(clang::ASTContext &Context) { |
| 48 | // Traversing the translation unit decl via a RecursiveASTVisitor |
| 49 | // will visit all nodes in the AST. |
| 50 | Visitor.TraverseDecl(Context.getTranslationUnitDecl()); |
| 51 | } |
| 52 | private: |
| 53 | // A RecursiveASTVisitor implementation. |
| 54 | FindNamedClassVisitor Visitor; |
| 55 | }; |
| 56 | |
| 57 | Using the RecursiveASTVisitor |
| 58 | ============================= |
| 59 | |
| 60 | Now that everything is hooked up, the next step is to implement a |
| 61 | RecursiveASTVisitor to extract the relevant information from the AST. |
| 62 | |
| 63 | The RecursiveASTVisitor provides hooks of the form bool |
| 64 | VisitNodeType(NodeType \*) for most AST nodes; the exception are TypeLoc |
| 65 | nodes, which are passed by-value. We only need to implement the methods |
| 66 | for the relevant node types. |
| 67 | |
| 68 | Let's start by writing a RecursiveASTVisitor that visits all |
| 69 | CXXRecordDecl's. |
| 70 | |
| 71 | :: |
| 72 | |
| 73 | class FindNamedClassVisitor |
| 74 | : public RecursiveASTVisitor<FindNamedClassVisitor> { |
| 75 | public: |
| 76 | bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| 77 | // For debugging, dumping the AST nodes will show which nodes are already |
| 78 | // being visited. |
| 79 | Declaration->dump(); |
| 80 | |
| 81 | // The return value indicates whether we want the visitation to proceed. |
| 82 | // Return false to stop the traversal of the AST. |
| 83 | return true; |
| 84 | } |
| 85 | }; |
| 86 | |
| 87 | In the methods of our RecursiveASTVisitor we can now use the full power |
| 88 | of the Clang AST to drill through to the parts that are interesting for |
| 89 | us. For example, to find all class declaration with a certain name, we |
| 90 | can check for a specific qualified name: |
| 91 | |
| 92 | :: |
| 93 | |
| 94 | bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| 95 | if (Declaration->getQualifiedNameAsString() == "n::m::C") |
| 96 | Declaration->dump(); |
| 97 | return true; |
| 98 | } |
| 99 | |
| 100 | Accessing the SourceManager and ASTContext |
| 101 | ========================================== |
| 102 | |
| 103 | Some of the information about the AST, like source locations and global |
| 104 | identifier information, are not stored in the AST nodes themselves, but |
| 105 | in the ASTContext and its associated source manager. To retrieve them we |
| 106 | need to hand the ASTContext into our RecursiveASTVisitor implementation. |
| 107 | |
| 108 | The ASTContext is available from the CompilerInstance during the call to |
| 109 | CreateASTConsumer. We can thus extract it there and hand it into our |
| 110 | freshly created FindNamedClassConsumer: |
| 111 | |
| 112 | :: |
| 113 | |
| 114 | virtual clang::ASTConsumer *CreateASTConsumer( |
| 115 | clang::CompilerInstance &Compiler, llvm::StringRef InFile) { |
| 116 | return new FindNamedClassConsumer(&Compiler.getASTContext()); |
| 117 | } |
| 118 | |
| 119 | Now that the ASTContext is available in the RecursiveASTVisitor, we can |
| 120 | do more interesting things with AST nodes, like looking up their source |
| 121 | locations: |
| 122 | |
| 123 | :: |
| 124 | |
| 125 | bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| 126 | if (Declaration->getQualifiedNameAsString() == "n::m::C") { |
| 127 | // getFullLoc uses the ASTContext's SourceManager to resolve the source |
| 128 | // location and break it up into its line and column parts. |
| 129 | FullSourceLoc FullLocation = Context->getFullLoc(Declaration->getLocStart()); |
| 130 | if (FullLocation.isValid()) |
| 131 | llvm::outs() << "Found declaration at " |
| 132 | << FullLocation.getSpellingLineNumber() << ":" |
| 133 | << FullLocation.getSpellingColumnNumber() << "\n"; |
| 134 | } |
| 135 | return true; |
| 136 | } |
| 137 | |
| 138 | Putting it all together |
| 139 | ======================= |
| 140 | |
| 141 | Now we can combine all of the above into a small example program: |
| 142 | |
| 143 | :: |
| 144 | |
| 145 | #include "clang/AST/ASTConsumer.h" |
| 146 | #include "clang/AST/RecursiveASTVisitor.h" |
| 147 | #include "clang/Frontend/CompilerInstance.h" |
| 148 | #include "clang/Frontend/FrontendAction.h" |
| 149 | #include "clang/Tooling/Tooling.h" |
| 150 | |
| 151 | using namespace clang; |
| 152 | |
| 153 | class FindNamedClassVisitor |
| 154 | : public RecursiveASTVisitor<FindNamedClassVisitor> { |
| 155 | public: |
| 156 | explicit FindNamedClassVisitor(ASTContext *Context) |
| 157 | : Context(Context) {} |
| 158 | |
| 159 | bool VisitCXXRecordDecl(CXXRecordDecl *Declaration) { |
| 160 | if (Declaration->getQualifiedNameAsString() == "n::m::C") { |
| 161 | FullSourceLoc FullLocation = Context->getFullLoc(Declaration->getLocStart()); |
| 162 | if (FullLocation.isValid()) |
| 163 | llvm::outs() << "Found declaration at " |
| 164 | << FullLocation.getSpellingLineNumber() << ":" |
| 165 | << FullLocation.getSpellingColumnNumber() << "\n"; |
| 166 | } |
| 167 | return true; |
| 168 | } |
| 169 | |
| 170 | private: |
| 171 | ASTContext *Context; |
| 172 | }; |
| 173 | |
| 174 | class FindNamedClassConsumer : public clang::ASTConsumer { |
| 175 | public: |
| 176 | explicit FindNamedClassConsumer(ASTContext *Context) |
| 177 | : Visitor(Context) {} |
| 178 | |
| 179 | virtual void HandleTranslationUnit(clang::ASTContext &Context) { |
| 180 | Visitor.TraverseDecl(Context.getTranslationUnitDecl()); |
| 181 | } |
| 182 | private: |
| 183 | FindNamedClassVisitor Visitor; |
| 184 | }; |
| 185 | |
| 186 | class FindNamedClassAction : public clang::ASTFrontendAction { |
| 187 | public: |
| 188 | virtual clang::ASTConsumer *CreateASTConsumer( |
| 189 | clang::CompilerInstance &Compiler, llvm::StringRef InFile) { |
| 190 | return new FindNamedClassConsumer(&Compiler.getASTContext()); |
| 191 | } |
| 192 | }; |
| 193 | |
| 194 | int main(int argc, char **argv) { |
| 195 | if (argc > 1) { |
| 196 | clang::tooling::runToolOnCode(new FindNamedClassAction, argv[1]); |
| 197 | } |
| 198 | } |
| 199 | |
| 200 | We store this into a file called FindClassDecls.cpp and create the |
| 201 | following CMakeLists.txt to link it: |
| 202 | |
| 203 | :: |
| 204 | |
| 205 | set(LLVM_USED_LIBS clangTooling) |
| 206 | |
| 207 | add_clang_executable(find-class-decls FindClassDecls.cpp) |
| 208 | |
| 209 | When running this tool over a small code snippet it will output all |
| 210 | declarations of a class n::m::C it found: |
| 211 | |
| 212 | :: |
| 213 | |
| 214 | $ ./bin/find-class-decls "namespace n { namespace m { class C {}; } }" |
| 215 | Found declaration at 1:29 |
| 216 | |