[cfe-dev] [RFC] [GSoC] AST differencing

[Manuel Klimek via cfe-dev]

Hi Johannes,

I think this is a great area of research. For Java, for example, refaster (
http://errorprone.info/docs/refaster) exists which lets you express simple
code changes with "before / after" samples. If we can get something like
this based on Clang's AST, that would be most awesome - is this a direction
you're working towards?

Cheers,
/Manuel

On Thu, Jun 22, 2017 at 2:50 AM Johannes Altmanninger via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi,
>
> I have been working on creating a syntax tree differencing library.
> So far, my focus has been on getting the core algorithm right, some
> parts are missing.
>
> I have submitted a patch [1]. I already received some great feedback and
> I am always open to suggestions for improvement.
>
> Additionally, if you have ideas to discuss about this, please let me
> know, then I can keep it in mind while designing.
>
> I think it should be fairly easy to create a tool that uses the same
> output format as diff while only showing semantic changes. More advanced
> tools seem to be quite possible also.
>
> One difficulty I am facing so far is that extracting values of
> individual AST nodes requires me to manually combine all relevant
> attributes. The value of a node is all things that make it semantically
> different from other nodes of the same kind, except for its children.
>
> After an edit script has been computed it would be possible to apply it,
> but in order such an edit script it will be necessary to implement a way
> to do the opposite of extracting node information: updating the source
> code based on the previously extracted information (node value). It is
> probably not particularly difficult but it will require qutie some
> effort to do it in a way that it can work for any node.
>
>
> Johannes
>
> [1] https://reviews.llvm.org/D34329
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