[cfe-dev] Is there a tool that restores a previously saved AST?

[Douglas Gregor]

On Jul 8, 2013, at 12:46 PM, Daniel Albuschat <d.albuschat at gmail.com> wrote:

> Am Montag, 8. Juli 2013 schrieb Douglas Gregor :
> 
> On Jul 5, 2013, at 3:28 PM, Daniel Albuschat <d.albuschat at gmail.com> wrote:
> 
>> Hi there,
>> 
>> I recently started looking into the Clang project and have to admit that I would never have expected it to be that mature. And I really appreciate the design decisions that lead to Clang being that re-usable and flexible. I think you're doing each and every C++ programmer a great favor and Clang will spawn an immense number of awesome tools in the future that we previously might not have imagined being possible to implement.
>> 
>> Enough praising, here is my actual question:
>> Is there any tool that reads an AST, saves it to some file or database, and later is able to *restore* that AST completely (e.g. to be able to create LLVM IR from it)? I'm trying to do something similar, so it'd be nice to know whether someone did that before.
>> The precompiled header implementations should do something like this, shouldn't they? Is their AST representation complete, or are they missing things like control-flow?
> 
> Yes to everything. The precompiled header implementation serializes the entire AST. You can use clang -cc1’s ‘-emit-ast’ option to emit the serialized AST into a “.ast” file, which can then be used to generate LLVM IR. It hasn’t been extensively tested, and to my knowledge nobody is doing this in a production environment, but the test file test/Frontend/ast-codegen.c illustrates how to do it and that it isn’t *completely* broken.
> 
> 
> Thank you for your reply, Doug.
> 
> The reason I am interested in restoring and/or building an AST is because I am thinking about using Clang as the backend for a programming language. It will obviously be a subset of C++. It would be awesome to use libraries written in C++ in it. This means, at a minimum,  instantiating "simple" classes and calling functions. Think of "C++ light" with less baggage from C and more straightforward Syntax. I am going to evaluate whether building my own, simpler AST and translating it into the Clang AST might work.
> 
> Do you think that this is feasible, or is it doomed to fail for some obvious reasons?

Generating correct Clang ASTs from anything but parsed C++ code is going to be extremely complicated. I think you’re better off generating C++ directly, or simply keeping your language front end separate from Clang.

	- Doug


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