clang libtooling insert a new header safely

Question

I'm using clang's libtooling to modify some code and I'm trying to find a way to safely insert a header whenever my tool is used on a C file.

I've read What's the right way to match #includes (or #defines) using Clang's libtooling? question about match calls to the preprocessors but I'm still uncertain about using it to insert code.

What is the proper way to insert a new #include using libtooling rewriter?

Answer 1

AFAIK it is possible (The proposed variants are for c ++ but with some changes can be used for c).

I don't know what do you mean by "safely insert", but I see two ways:

1. Inserting #include near existing one. The problem here is to find existing #include. The possible way to do it described here: https://stackoverflow.com/a/44077744/6490190

2. Inserting include before the topmost TranslationUnitDecl or NamespaceDecl in AST. The idea is to start from some Stmt or Decl or Type in code and recursively visit all its parents: ASTContext::getParents() until TranslationUnitDecl or NamespaceDecl is found.

   Example can be found here:

   • https://github.com/YulyIllarionov/Cpp-14-Regress/blob/master/cpp14regress/inc/lambda.h,
   • https://github.com/YulyIllarionov/Cpp-14-Regress/blob/master/cpp14regress/src/lambda.cpp