[PATCH] D80514: [clang-tidy] modernize-use-trailing-return-type support for C++20 concepts and decltype

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman accepted this revision.
aaron.ballman added a comment.
This revision is now accepted and ready to land.

In D80514#2206019 <https://reviews.llvm.org/D80514#2206019>, @bernhardmgruber wrote:

> Btw: what is the general rule for Phabricator reviews here when to tick the `Done` checkbox of a comment? What is the semantic of this checkbox? Is the ticked state the same for everyone?

I don't think we have any hard-and-fast rules for it and I suspect the ticked state differs from review to review. Personally, I appreciate when the person who was asked to do some work is the one to check the Done box signalling that they think it's done (whether it's an author fixing a comment from a reviewer or a reviewer answering a question from an author, etc). This tells me "hey, someone thinks this is done, go look at it and comment if you disagree." However, I am guessing others have a different workflow.

I don't think I have any further concerns with this patch, so LGTM.



================
Comment at: clang-tools-extra/clang-tidy/modernize/UseTrailingReturnTypeCheck.cpp:430
+      AT->getKeyword() == AutoTypeKeyword::Auto &&
+      !hasAnyNestedLocalQualifiers(F->getDeclaredReturnType()))
+    return;
----------------
bernhardmgruber wrote:
> aaron.ballman wrote:
> > aaron.ballman wrote:
> > > bernhardmgruber wrote:
> > > > aaron.ballman wrote:
> > > > > Why do we need to check that there aren't any nested local qualifiers?
> > > > Because I would like the check to rewrite e.g. `const auto f();` into `auto f() -> const auto;`. If I omit the check for nested local qualifiers, then those kind of declarations would be skipped.
> > > I'm still wondering about this.
> > > Because I would like the check to rewrite e.g. const auto f(); into auto f() -> const auto;. If I omit the check for nested local qualifiers, then those kind of declarations would be skipped.
> > 
> > I don't think I understand why that's desirable though? What is it about the qualifier that makes it worthwhile to repeat the type like that?
> Thank you for insisting on that peculiarity! The choice is stylistically motivated to align function names:
> 
> ```
> auto f() -> int;
> auto g() -> std::vector<float>;
> auto& h();
> const auto k();
> decltype(auto) l();
> ```
> vs.
> ```
> auto f() -> int;
> auto g() -> std::vector<float>;
> auto h() -> auto&;
> auto k() -> const auto; 
> auto l() -> decltype(auto);
> ```
> 
> But judging from your response, this might be a surprise to users. Would you prefer having an option to enable/disable this behavior?
> But judging from your response, this might be a surprise to users. Would you prefer having an option to enable/disable this behavior?

Maybe it will be, maybe it won't. :-D The reason I was surprised was because it feels like a formatting related choice rather than a modernization related choice. However, I've always struggled to understand the utility of this check (it's one I  disable in every .clang-tidy configuration file I can), so my reasoning may be flawed. I feel like the goal of this check isn't to format code nicely, it's to modernize to using a trailing return type where that adds clarity. But I don't think `auto& func()` changing into `auto func() -> auto&` adds clarity (I think it removes clarity because the second signature is strictly more complex than the first), and similar for qualifiers. However, I think the exact same thing about `int func()` changing into `auto func() -> int`.

Given that we document this function to rewrite all functions to a trailing return type signature, I guess the behavior you've proposed here is consistent with that goal and so I'm fine with it.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D80514/new/

https://reviews.llvm.org/D80514