[cfe-dev] [llvm-dev] [RFC] clang support for API information generation in JSON

[Mats Larsen via cfe-dev]

Hi Zixu, I just wanted to say that this is of interest to me!

I work on a couple of FFI generation tools, and something like this would
make it easier
for us to generate code from headers. The clang AST is pretty scary so a
tool like this
would definitely be appreciated.

Best regards
Mats Larsen

On Wed, Sep 1, 2021 at 8:19 PM Zixu Wang via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi All!
>
> I’m writing to propose clang-extract-api, a tool to collect and serialize
> API information from header files, for example function signatures,
> Objective-C interfaces and protocols, and inline documentation comments. We
> hope it could help future tools to understand clang-based language APIs
> without needing to dig into the AST themselves.
>
>
> *Background*
> *Motivation*
>
> Library and SDK providers may find it useful to be able to create and
> inspect a “snapshot” of APIs they expose, for example, to check for
> API/ABI-breaking changes between two versions, or to automate generating
> documentation for the APIs. Here is a list of examples of information we
> want to extract from APIs:
> • the name (spelling/mangled) of the symbol;
> • the unique identifier of the symbol, for example the Unified Symbol
> Resolution (USR);
> • the source location of the API declaration (file, line, column);
> • access control of the API (public/private/protected);
> • availability (available/unavailable/deprecated);
> • function signatures (return/parameters);
> • documentation comments attached to a symbol;
> • relations with other symbols (class methods, typedef relations, struct
> data fields, enum constants, etc.)
> Since these API information is available in the header files, which
> declare and distribute the APIs, we can implement a tool to extract them
> without invoking a compilation of the whole project to enable easy access
> to the information for tooling.
>
> *Existing solutions*
>
> While there are some existing solutions in clang to dump symbols or AST
> information, they either expose unnecessary low-level details or fail to
> provide enough information of APIs. For example, clang -ast-dump dumps
> low-level details for all declarations for debug purposes and the output is
> not machine-parsable. Doxygen also extracts documentation comments and
> other information from API declarations, but its output is rendered
> documentation in web formats which is not flexible for other uses and tools.
>
> *Proposal*
>
> We propose to implement this tool as a new frontend action invoked by
> `clang -extract-api` as show in the example below.
>
> clang -extract-api \
>   header.h [more_header.h ...] or a filelist\
>   -isysroot <SDK> \
>   -target <TARGET> \
>   -I <INCLUDE PATH> \
>   -isystem <SYS INCLUDE PATH> \
>   ...
>   -o output.json
>
> It takes in the header file(s) or a filelist file containing paths to the
> header file(s) as the input. The header files will be parsed by clang and
> the extract-api action will visit the AST to extract needed information and
> serialize to a JSON output. Please find an example input and output
> attached.
>
> The example output is based on the symbol graph format that's already used
> by Swift for serializing symbol information and their relations. This
> format can represent the required API information and is flexible and
> extendable as demonstrated in the example so we think it's a good starting
> point.
>
> We are excited about this idea and its potential uses, and we’d love to
> hear feedback and suggestions!
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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