[libc++-14] <ranges> header fails to define std::ranges::contiguous_range

[Wentzell]

The code snippet

#include <ranges>

template <std::ranges::contiguous_range R>
void f(R r){}

compiles successfully (using -stdlib=libc++ -std=c++20) with clang-13.0.1 and clang-trunk,
but fails to compile with clang-14.0.0

<source>:3:24: error: no type named 'contiguous_range' in namespace 'std::ranges'
template <std::ranges::contiguous_range R>
          ~~~~~~~~~~~~~^
<source>:4:8: error: unknown type name 'R'
void f(R r){}
       ^
2 errors generated.
Compiler returned: 1

See https://godbolt.org/z/1na3EaeEe

[llvmbot]

@llvm/issue-subscribers-c-20

[DimitryAndric]

@ldionne maybe this has to do with commits add3ab7 and 3f43d80 just not making it into 14.0.0?

@Wentzell I'm assuming you are using the exact 14.0.0 release tag, not the release/14.x branch?

[Wentzell]

Yes this was using the exact 14.0.0 tag. I have not tried if the issue persists on 14.x

[Wentzell]

I can confirm that this issue persists with 14.0.1.

[philnik777]

@DimitryAndric No, this has nothing to do with the span stuff, but it's the same type of error.
It looks like std::ranges::contiguous_range is guarded under _LIBCPP_HAS_NO_INCOMPLETE_RANGES, but has already been shipped in libc++ 13.
@tstellar Is there still time for LLVM 14 patches? If that's the case I'll write a patch. Otherwise I think it's not yet widely used enough to matter very much, so I wouldn't change it for libc++15 again. Although we might be able to ship ranges in LLVM 15, so it wouldn't matter in that case.

[tstellar]

@philnik777 We are still accepting LLVM14 patches.

[var-const]

@tstellar What is the deadline for a patch to still be accepted for LLVM 14?

[tstellar]

@var-const Probably around June 1. June 8 is the last planned 14.0.x release.

[DavidKeller]

@philnik777 Our code base is using these concepts since clang-13. So we're particularly interested in the fix.

Is this fix just a matter of removing the _LIBCPP_HAS_NO_INCOMPLETE_RANGES guard around the concept definitions ?

[philnik777]

No, the concepts require other parts of ranges and we'd like to keep the amount of available ranges-stuff low until we implement all of the one ranges proposal. I'll try to get the fix working in the next few days. I have been procrastinating on that a bit.

[DavidKeller]

Please let me know if I can be of any help.

[Wentzell]

@philnik777 Thank you for looking into this!

It seems the fix was committed to main. However the issue only ever showed for the llvm 14.0.x releases.
Shouldn't the fix go into the 14.x branch?

[philnik777]

@Wentzell The fix will go into the 14.x branch. This is also a fix for the libc++15 release, since I don't think we will complete the one ranges proposal in the libc++15 time frame. But we should get it done for libc++16. @ldionne or @tstellar (?) will put it in the 14.x branch. I don't know the process for this.

[Wentzell]

Thank you for clarifying!

[tstellar]

@ldionne Is this Ok to backport? b177a90

[tstellar]

/cherry-pick b177a90

[llvmbot]

Failed to cherry-pick: b177a90

https://github.com/llvm/llvm-project/actions/runs/2432601260

Please manually backport the fix and push it to your github fork. Once this is done, please add a comment like this:

/branch <user>/<repo>/<branch>

[tstellar]

Is someone able to backport this to a personal branch so we can create a pull request?

[tstellar]

Merged: 4d039a7

[ldionne]

Yeah, sorry, I forgot to comment here but I already cherry-picked to release/14.x some time ago:

commit 55e34f3b49b1485d57ba2e4b8cd88af8f7900f61
Author: Nikolas Klauser <[email protected]>
Date:   Thu May 12 15:46:18 2022 +0200

    [libc++] Always enable the ranges concepts

    The ranges concepts were already available in libc++13, so we shouldn't guard them with `_LIBCPP_HAS_NO_INCOMPLETE_RANGES`.
    Fixes https://github.com/llvm/llvm-project/issues/54765

    Differential Revision: https://reviews.llvm.org/D124011

    (cherry picked from commit b177a90ce7b590dfce6479142f46fd1b9554a3b3)