[cfe-dev] [RFC] Easier source-to-source transformations with clang tooling

[Manuel Klimek via cfe-dev]

On Thu, Jan 24, 2019 at 11:56 AM Jonas Toth <development at jonas-toth.eu>
wrote:

> Hi,
>
> one question that came to my mind because of Joel's Mail:
>
> Is it possible to run in multiple passes?
> My use-case is adding `const` to variables that could be 'const' but
> aren't. If you declare multiple variables like `int not_const,
> const_variable;`
> the transformation requires splitting these up, first -> `int not_const;
> int const_variable;` and then do the `const` transformation -> `int
> not_const; const int const_variable;`.
>
> I have implemented both transformations in clang-tidy (only partially
> landed yet) but there is no easy way I can run them in one check. The
> current workflow
> pretty much forces us to run clang-tidy multiple times and converge to the
> final solution.
>
> If your framework could give an improvement in this place, would be
> awesome! And I think worth to consider anyway If we change the way
> we do transformations.
>

Generally, you can already do this, but it'd be outside clang-tidy. You can
write a clang tool that
a) runs over the codebase and stores the "const graph"
b) load the "const graph" into memory and generate all the replacements
(there's a way to create yaml replacements)
c) apply all the replacements



> Best, Jonas
> Am 16.11.18 um 16:22 schrieb Yitzhak Mandelbaum via cfe-dev:
>
> Hi all,
>
> I have a proposal for a framework that makes it easier to write source to
> source transformations with the clang::Tooling libraries, including
> clang-tidy checks.
>
> The full proposal is in this doc:
>
>
> https://docs.google.com/document/d/1ppw0RhjwsrbBcHYhI85pe6ISDbA6r5d00ot3N8cQWeQ/edit?usp=sharing
>
> From the doc:
> Transformer is a framework that aims to simplify development of
> clang-based source-to-source transformations.  It focuses on the particular
> class of transformations that act only locally — that is, use local
> information about the code and make local changes  (like a syntax-aware
> “find-and-replace”); and at scale — that is, will be carried out on many
> source files.  The target audience is users that are comfortable with, or
> willing to become comfortable with, the clang AST matchers library.
>
> I have a working prototype of this library which I've used on small
> examples inside Google.  I plan to put together a patch for reference
> next week, although the doc should stand on its own.
>
> Thanks!
> Yitzhak Mandelbaum
>
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