[PATCH] D99861: [Clang] Record tokens in attribute arguments for user-defined C++/C2x attributes

Fri Apr 16 09:08:41 PDT 2021

aaron.ballman added a comment.

In D99861#2694605 <https://reviews.llvm.org/D99861#2694605>, @urnathan wrote:

> See also https://bugs.llvm.org/show_bug.cgi?id=46446.  when I first fell into this issue, I did think it was trying to save the token stream as this patch is doing.  Neat I thought :)  although I'm a clang weenie, saving the tokens is putting this into deferred-parse territory, which makes me nervous.

FWIW, I've been stewing on the deferred parse issues with the approach from this patch because they make me nervous as well. Because `[[]]` attributes can have arbitrary token soup for their arguments and that includes arbitrary expressions, I worry that just giving the plugin author a bunch of tokens and saying "you deal with it" will only work for very trivial arguments.

> Wouldn't it be better for the ParsedAttrInfo objects to determine whether and how to parse their arguments.  They could do so immediately, or save tokens, or whatever on a per-attribute per-argument basis.  Isn't that more flexible?  Add some ParsedAttrInfo defaults for the default cxx11, gnu & clang flavours of attributes?

I think this would be an improved approach over just replaying the tokens for the plugin to handle. I would hope that we'd be able to design something that handles the easy cases of passing a string literal, an integer value, an enumerated list of named values, etc so that plugin authors don't have to reinvent the wheel for basic needs.

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https://reviews.llvm.org/D99861