RecursiveASTVisitor class from clangAST library

1. What's RecursiveASTVisitor?

RecursiveASTVisitor class is defined at the file ${LLVM_PROJECT_PATH}/clang/include/clang/AST/RecursiveASTVisitor.h.

2. Macros in RecursiveASTVisitor

There are many macros in the RecursiveASTVisitor.h file:

StmtNodes.inc, TypeNodes.inc, TypeLocNodes.def, DeclNodes.inc, OMP.inc, AttrVisitor.inc

2.1 TRAVERSE_STMT_BASE(NAME, CLASS, VAR, QUEUE)

If this class(RecursiveASTVisitor) and Derived class have the same "Traverse##NAME" function, then

convert '*this' into Derived type and call "Traverse##NAME" function with 'VAR' and 'QUEUE'.

If not, convert '*this' into Derived type and call "Traverse##NAME" function with 'VAR'.

 1   // Traverse the given statement. If the most-derived traverse function takes a
 2   // data recursion queue, pass it on; otherwise, discard it. Note that the
 3   // first branch of this conditional must compile whether or not the derived
 4   // class can take a queue, so if we're taking the second arm, make the first
 5   // arm call our function rather than the derived class version.
 6 #define TRAVERSE_STMT_BASE(NAME, CLASS, VAR, QUEUE)                            
 7   (::clang::detail::has_same_member_pointer_type<                              
 8        decltype(&RecursiveASTVisitor::Traverse##NAME),                         
 9        decltype(&Derived::Traverse##NAME)>::value                              
10        ? static_cast<std::conditional_t<                                       
11              ::clang::detail::has_same_member_pointer_type<                    
12                  decltype(&RecursiveASTVisitor::Traverse##NAME),               
13                  decltype(&Derived::Traverse##NAME)>::value,                   
14              Derived &, RecursiveASTVisitor &>>(*this)                         
15              .Traverse##NAME(static_cast<CLASS *>(VAR), QUEUE)                 
16        : getDerived().Traverse##NAME(static_cast<CLASS *>(VAR)))

2.2 STMT(CLASS, PARENT) and StmtNodes.inc

Using the StmtNodes.inc file and STMT() macro define the Traverse##CLASS() function.

2.2.1 CLASS

The 'CLASS' would be any statement: BreakStmt, CXXCatchStmt, CXXForRangeStmt, CXXTryStmt,

CapturedStmt, CompoundStmt, ContinueStmt, CoroutineBodyStmt, DeclStmt, DoStmt, ForStmt,

GotoStmt, IfStmt, IndirectGotoStmt, MSDependentExistsStmt, NullStmt, ObjCAtCatchStmt, ObjCAtFinallyStmt,

ObjCAtSynchronizedStmt, ObjCAtThrowStmt, ObjCAtTryStmt, ObjCAutoreleasePoolStmt,

ObjCForCollectionStmt, ReturnStmt, CaseStmt, DefaultStmt, AttributedStmt, LabelStmt, WhileStmt, ... ...

1 // Declare Traverse*() for all concrete Stmt classes.
2 #define ABSTRACT_STMT(STMT)
3 #define STMT(CLASS, PARENT) 
4   bool Traverse##CLASS(CLASS *S, DataRecursionQueue *Queue = nullptr);
5 #include "clang/AST/StmtNodes.inc"

2.3 Define the WalkUpFrom##Class() and Visit##CLASS() functions

By defining the WalkUpFrom##CLASS() and Visit##CLASS() functions to provide the defualt implementations for

RecursiveASTVisitor class. The values of 'CLASS' are the same as "2.2.1 CLASS".

 1   // Define WalkUpFrom*() and empty Visit*() for all Stmt classes.
 2   bool WalkUpFromStmt(Stmt *S) { return getDerived().VisitStmt(S); }
 3   bool VisitStmt(Stmt *S) { return true; }
 4 #define STMT(CLASS, PARENT)                                                    
 5   bool WalkUpFrom##CLASS(CLASS *S) {                                           
 6     TRY_TO(WalkUpFrom##PARENT(S));                                             
 7     TRY_TO(Visit##CLASS(S));                                                   
 8     return true;                                                               
 9   }                                                                            
10   bool Visit##CLASS(CLASS *S) { return true; }
11 #include "clang/AST/StmtNodes.inc"

3. Traversal

3.1 Type Traversal

3.2 TypeLoc Traversal

3.3 Decl Traversal

3.4 Stmt Traversal

4. Preprocessing this file

The file contains a lot of macros, we will preprocess this file to get the preprocessed file.

// LLVM_PROJECT_PATH is the root path of llvm project.
// 
// Using `export LLVM_PROJECT_PATH = ` to declare this env.
clang --trace-includes -D__cplusplus=201402L 
-I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ 
-I${LLVM_PROJECT_PATH}/clang/include/ 
-I${LLVM_PROJECT_PATH}/.build_RelWithDebInfo/tools/clang/include/ 
-I${LLVM_PROJECT_PATH}/.build_RelWithDebInfo/include/ 
-I${LLVM_PROJECT_PATH}/llvm/include/ 
-E RecursiveASTVisitor.h -o tmp.ii

4.1 Delete the Blank Line

Open your code in Visual Studio Code.
From Edit Menu, select Replace or use a short cut key ( command + Option + F on Mac or Ctrl + H on Windows)
In the find box type ^(s)*$n.
Leave the replace box empty.
Make sure the 'Use Regular Expression' is selected.
Select the 'Replace All' button.

4.2 Delete the Linemarker

The linemarker line is like the following:

# 163 "/LLVM/llvm-project/.build_RelWithDebInfo/tools/clang/include/clang/AST/DeclNodes.inc"

To delete the linemarker, as the "4.1 Delete the Blank Line" section, we replace the regex in step 3 with "^#(.)+$n".

4.3 Delete the header files

Delete the codes from including header files.

The result of preprocessing RecursiveASTVisitor.h using clang -E is at https://gist.github.com/vitonzhangtt/8a1434c22d956bad8cd52259fc7044b0.

Reference

1. clang::RecursiveASTVisitor< Derived > Class Template Reference

A class that does preorder or postorder depth-first traversal on the entire Clang AST and visits each node.

https://clang.llvm.org/doxygen/classclang_1_1RecursiveASTVisitor.html

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