[libc++] Implement `operator<=>` for `shared_ptr`

[avogelsgesang]

Summary

Implements part of:

• P1614R2 The Mothership has Landed

Fixes LWG3427

[Mordante]

Thanks for your contribution! When resolving the review comments please look whether they apply to your other patches too. (I first want to look at this patch, once approved I'll look at the others.)

For the CI, feel free to ignore the error of the format CI, this is a soft-error at the moment.

libcxx/docs/ReleaseNotes.rst

44 ↗

(On Diff #448878)

We usually only mention "larger" improvements here not every subpart of a paper.

libcxx/include/__memory/shared_ptr.h

1241

1242

The macro only needs to be used in code that works in C++03.

1242

please use __x and __y for consistency.

1353

I see this matches the Wording in the Standard, but it differs from the paper. Does this complete an LWG issue?

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.cmp/cmp_nullptr.pass.cpp

48

Partly pre-existing, but I miss tests to validate the return type and that the function is noexcept. Can you add tests for this? See D128603 for examples.

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.cmp/order.pass.cpp

8–9 ↗

(On Diff #448878)

24 ↗

(On Diff #448878)

Please remove this #if the UNSUPPORTED is the libc++ way to achieve this behaviour.

32 ↗

(On Diff #448878)

Please test all equality and comparison operators.

[avogelsgesang]

Address comments by @Mordante

[avogelsgesang]

Thanks for your contribution!

Thank you for your review!

When resolving the review comments please look whether they apply to your other patches too. (I first want to look at this patch, once approved I'll look at the others.)

I will do so. I will let you know as soon as the other reviews are updated (probably only after we land this one, so I don't have to update the other commits multiple times)

libcxx/docs/ReleaseNotes.rst

44 ↗

(On Diff #448878)

works for me - that also gets rid of the annoying merge conflict on this line which I will have with all of the other posted reviews

libcxx/include/__memory/shared_ptr.h

1353

Indeed, this fixes https://github.com/cplusplus/draft/commit/28430c71f1f3ce39f6c9a9509756bfcece270203, also known as https://cplusplus.github.io/LWG/issue3427

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.cmp/cmp_nullptr.pass.cpp

48

Added calls to AssertComparisonsAreNoexcept, AssertComparisonsReturnBool, AssertOrderAreNoexcept, etc.

My code required additional #ifdefs, though.
Would it make sense to introduce AssertOrderReturn also for dialects < C++20, and let it gracefully degrade to AssertComparisonsReturnBool on those earlier C++ versions?

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.cmp/order.pass.cpp

32 ↗

(On Diff #448878)

Those were already tested in lt.pass.cpp and eq.pass.cpp.
I do agree, though, that the splitting across multiple files made it hard to judge the existing test coverage. Hence, I merged this test with the pre-existing lt.pass.cpp and eq.pass.cpp.
I think doing so improves readability of this test case.

[avogelsgesang]

Forgot to git add the _LIBCPP_HIDE_FROM_ABI

[avogelsgesang]

Fix templates so they also build on C++03

[avogelsgesang]

add missing include

[Mordante]

In general I'm happy, one nit remaining. I like to see the CI green before approving.

libcxx/include/__memory/shared_ptr.h

1242

Seems you missed the noexcept here, but I see it's fixed at the other location.

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.cmp/cmp_nullptr.pass.cpp

48

No I think that doesn't make sense since it changes the macro depending on the language version used. In libc++ and its tests we're used to using #if often. Sometimes we have some helper macros, but only for generic things like CONSTEXPER_AFTER_XX.

[avogelsgesang]

• Use noexcept instead of macro
• Rebase on D130855
• (Hopefully) fix CI by adding missing include (?)

[avogelsgesang]

Status: Done -> Complete

[Mordante]

Thanks, LGTM!
I'll commit this on your behalf.