Source-to-Source transformation (as a plugin?) - state of the art

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Source-to-Source transformation (as a plugin?) - state of the art

Alex Denisov via cfe-dev

Hi everybody,

As a beginner with clang I am struggling to support source-to-source transformation in one step with clang.

How is the state of the art in source-to-source transformation with clang?

I followed almost every resource on the Web and I can achieve to do source rewrites (Rewriter) via a clang plugin, but the final binary is not updated (the CodeGen is the main activity, and it is compiled regardless of what I have modified in my plugin, even using AddBeforeMainAction in the getActionType).

I have seen some documents regarding libTooling and how to create an independent program that uses clang as library, but my purpose it is to create a plugin (FrontendPluginRegistry::Add<>, something "easy" to plug to a non-custom clang binary) and achieve source-to-source modifications (transparently to the users, avoiding overwriting their source files).

Being a bit pedantic, in case it is not clear: I need something like a "plugin" to extend clang in an easy way. I need something that is "integrated" in the compiling process. Why? because I need to modify the source code during the compilation phase, inject new code, modify the source code from the user in one step (I don't want to create a tool to parse the user source code and then compile the output files). Also, I would like to distribute my code (plugin) to allow users to use it by themselves.

It is mandatory that it is during the compilation phase of clang (clang $FLAGS $PLUGIN $ETC -o program source_files...).

*Use cases I would like to try:*
- 1. I would like to transform the source code in a really fast and confident way, even before the lexer. I don't know if it is possible. Like having a stream of text and transforming, previous to the preprocessor/lexer. I know it can be dangerous, but at least to know if I can and *how to proceed*.
- 2. I would like to transform specific parts of the source code (can be with the Rewriter, as I have achieved). For that, I use the ASTConsumer and Visitor pattern. Then, I would like to rewrite, inject text, etc. *So far I know how to do it, but not how to preserve for the CodeGen (main action) and create the final binary with it (reparsing again the source code and going through every phase).*
- 3. I would like to create AST Nodes. Although I have read it is not the best option, I would like to be able to add new nodes, statements, etc. *I didn't try yet this phase, but any guess?*

Regards, rNoz

Some threads, repositories or blogs that I have reviewed and tested. In some of them there are answers that don't work: 

I mark the "most important" in bold. The second one just hits the knot, I am in the same "state" as him.

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