[cfe-dev] RFC: Easier AST Matching by Default

[Aaron Ballman via cfe-dev]

I've not seen much to suggest the community is not in favor of this
direction, so I think you're all set to post patches for review. If
there are community concerns, we can address them during the review
process. Thank you for working on this!

~Aaron

On Fri, Dec 20, 2019 at 6:03 PM Stephen Kelly <steveire at gmail.com> wrote:
>
>
> Matchers are orthogonal to Syntax Trees as laid out in that document:
>
> ```
>
> Will we end up needing to reinvent matchers for this representation?
>
> **We want to avoid this.**
>
> Matchers are a complicated beast and having a separate set of those for syntax trees would be unfortunate. Moreover, syntax trees lack the semantic information that the users of AST matchers often rely on. If one wants to take advantage of the concept of matchers and syntax trees, they have options to do so based on existing implementation of ASTMatchers, e.g. they could:
>
> use ASTMatchers to find interesting Clang AST nodes,
>
> find their syntax tree counterparts,
>
> apply transformations to syntax trees.
>
> ```
>
>
> Thanks,
>
> Stephen.
>
> On 20/12/2019 22:02, Gábor Horváth wrote:
>
> Hi!
>
> I like the idea of making writing tools/prototypes easier. But if the goal is to get rid of invisible nodes when matching I wonder if this would somewhat overlap with syntax trees [1]. Adding Dmitri and Ilya in case they have an opinion on that.
>
> Cheers,
> Gabor
>
> [1]: https://docs.google.com/document/d/161XftOcF-ut1pGQr5ci9kXd_y0jRQl3y9sVyvuEkLDc/edit#heading=h.cwnlr9q7jmlp
>
> On Fri, Dec 20, 2019 at 1:06 PM Aaron Ballman via cfe-dev <cfe-dev at lists.llvm.org> wrote:
>>
>> On Fri, Dec 20, 2019 at 4:01 PM Stephen Kelly via cfe-dev
>> <cfe-dev at lists.llvm.org> wrote:
>> >
>> >
>> > Hi,
>> >
>> > (Apologies if you receive this twice. GMail classified the first one as
>> > spam)
>> >
>> > Aaron Ballman and I met by chance in Belfast and we discussed a way
>> > forward towards making AST Matchers easier to use, particularly for C++
>> > developers who are not familiar with the details of the Clang AST.
>> >
>> > For those unaware, I expanded on this in the EuroLLVM conference this
>> > year, and then expanded on it at ACCU:
>> >
>> >   https://steveire.wordpress.com/2019/04/30/the-future-of-ast-matching
>> >
>> > One step in the process of getting there is changing the default
>> > behavior of AST Matchers to ignore invisible nodes while matching using
>> > the C++ API, and while matching and dumping AST nodes in clang-query.
>> >
>> > I think this is the most important change in the entire proposal as it
>> > sets out the intention of making the AST Matchers easier to use for C++
>> > developers who are not already familiar with Clang APIs.
>> >
>> > To that end, I've written an AST to motivate the change:
>> >
>> >
>> > https://docs.google.com/document/d/17Z6gAwwc3HoRXvsy0OdwU0X5MFQEuiGeSu3i6ICOB90
>> >
>> > We're looking for feedback before pressing forward with the change. I
>> > already have some patches written to port clang-tidy and unit tests to
>> > account for the change of default.
>>
>> I'm generally in favor of this path forward. I think this is the
>> correct default and allows a more gentle introduction to AST matchers
>> for people new to the project (which helps with introducing new
>> clang-tidy checks) while still allowing people who need to get into
>> the nitty gritty details of the AST to do so as needed. Thank you for
>> the efforts!
>>
>> CCing Manual, Alex, and Sam because they do a lot of work on the
>> matcher interfaces as well.
>>
>> ~Aaron
>>
>> >
>> > Thanks,
>> >
>> > Stephen.
>> > _______________________________________________
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>> > cfe-dev at lists.llvm.org
>> > https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
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