[libc++] Implements ranges::enable_borrowed_range

[Mordante]

Summary

This is the initial patch to implement ranges in libc++.

Implements parts of:

• P0896R4 One Ranges Proposal
• P1870 forwarding-range is too subtle
• LWG3379 in several library names is misleading

[curdeius]

Don't forget to add the new <ranges> header to std_includes test. Otherwise no other remarks from my side.

[curdeius]

I meant double_include: https://github.com/llvm/llvm-project/blob/master/libcxx/test/libcxx/double_include.sh.cpp.

[Mordante]

In D90999#2380694, @curdeius wrote:

Don't forget to add the new <ranges> header to std_includes test. Otherwise no other remarks from my side.

Thanks for the pointer. I'll update the patch shortly.

[Mordante]

Added the double_include.sh.cpp test as suggested by @curdeius.
move a test from ranges/ranges to ranges/range.range.

[tschuett]

https://github.com/llvm/llvm-project/blob/57b3bc8c603e25380ba56a5b95b2887010e9c1c0/libcxx/NOTES.TXT#L20

[Mordante]

In D90999#2380758, @tschuett wrote:

https://github.com/llvm/llvm-project/blob/57b3bc8c603e25380ba56a5b95b2887010e9c1c0/libcxx/NOTES.TXT#L20

Thanks, I'll look at what else I've missed.

[Mordante]

Added the other steps required when adding a new header as suggested by @tschuett.

[miscco]

I am wondering whether we should split the ranges header up into a smaller part that we use to include in other headers adn the rest.

Including all of ranges just for one trait seems a bit of an overkill.

We could always add it to concepts as that should be a transitive include for everything that includes range. Thoughts @ldionne?

libcxx/include/ranges

16

I am slightly surprised that concepts is not required

23

I am wondering whether it is wise to copy the synopsis as it should be rather than how it is. This might trick the user to believe all of it is supported. What are the conventions here?

libcxx/test/std/ranges/range.range/enable_borrowed_range.pass.cpp

24 ↗

(On Diff #303636)

I believe you are missing coverage for all the ranges that are not borrowed, e.g. vector, list, ...

[tschuett]

libcxx/include/ranges

326

Why is the curly bracket not at the end of the line above?

[Mordante]

In D90999#2381043, @miscco wrote:

I am wondering whether we should split the ranges header up into a smaller part that we use to include in other headers adn the rest.

Including all of ranges just for one trait seems a bit of an overkill.

I agree including the full ranges header in string_view and span feels a bit overkill. But I'll leave the decisions whether or not to split the header with the libc++ maintainers.

libcxx/include/ranges

16

Agreed. For this patch I don't need concepts, but std::ranges::begin() will require them.

23

Looking at other headers it does they do the same for example concepts also uses 'unspecified' and 'see below'.

326

Because that's what 'chrono' uses. However I have no objection against putting it on one line. Not sure what the libc++ coding style has to say about this.

libcxx/test/std/ranges/range.range/enable_borrowed_range.pass.cpp

24 ↗

(On Diff #303636)

I'm not convinced they really need to be tested, but adding them is not much effort. So I'll add them.

[Mordante]

Adds the additional unit tests as requested by @miscco.
Found some accidental tabs in the patch replaced them with spaces.

[Mordante]

Change the unit tests to compile time test, based on the review comment in D91004.

[ldionne]

In D90999#2381043, @miscco wrote:

I am wondering whether we should split the ranges header up into a smaller part that we use to include in other headers adn the rest.

Including all of ranges just for one trait seems a bit of an overkill.

We could always add it to concepts as that should be a transitive include for everything that includes range. Thoughts @ldionne?

I'd be fine with splitting various parts of ranges into separate headers if that makes the implementation clearer, etc.

[Mordante]

Move the enable_borrowed_range to a helper header to avoid including <ranges> in <span> and <string_view> as suggested by @miscco.

[Mordante]

Implement all new header tests as suggested by @curdeius in D92214.

[Mordante]

Rebased.

[Mordante]

• Removed unimplemented part of the synopsis
• Ran clang-format on the patch
• Rebased to trigger CI again

[Mordante]

Rebase to trigger CI. The last build failed, but so did main.

[Mordante]

Rebased to trigger CI.

[Mordante]

@ldionne Friendly ping.