[libc++][ranges] P3059R2: Making user-defined constructors of view iterators/sentinels private - #193891

Pre-requisite for: #193891

Pre-requisite for: llvm/llvm-project#193891

Pre-requisite for: llvm/llvm-project#193891

As a pre-requisite for llvm#193891

As a pre-requisite for #193891

…ests (#210687)

As a pre-requisite for llvm/llvm-project#193891

…ests (#210687)

As a pre-requisite for llvm/llvm-project#193891

…211252)

As a pre-requisite to: #193891

….pass.cpp` (#211252)

As a pre-requisite to: llvm/llvm-project#193891

….pass.cpp` (#211252)

As a pre-requisite to: llvm/llvm-project#193891

…0 merge (#213062)

Consistency improvements and other small tweaks.

A follow-up to #193891 - the
changes were deferred to reduce the size of an already large and
approved PR.

… after P3050 merge (#213062)

Consistency improvements and other small tweaks.

A follow-up to llvm/llvm-project#193891 - the
changes were deferred to reduce the size of an already large and
approved PR.

…0 merge (#213062)

Consistency improvements and other small tweaks.

A follow-up to llvm/llvm-project#193891 - the
changes were deferred to reduce the size of an already large and
approved PR.
Signed-off-by: Hafidz Muzakky <ais.muzakky@gmail.com>

…0 merge (llvm#213062)

Consistency improvements and other small tweaks.

A follow-up to llvm#193891 - the
changes were deferred to reduce the size of an already large and
approved PR.

… after P3050 merge (#213062)

Consistency improvements and other small tweaks.

A follow-up to llvm/llvm-project#193891 - the
changes were deferred to reduce the size of an already large and
approved PR.

…erators/sentinels private (llvm#193891)

Implements https://wg21.link/P3059R2 (DR)

Closes llvm#189599

1. Made constructors of iterator and sentinel types of the following
views private:
  - `iota_view`
  - `basic_istream_view`
  - `filter_view`
  - `transform_view`
  - `take_view`
  - `take_while_view`
  - `join_view`
  - `lazy_split_view`
  - `split_view`
  - `elements_view`
2. Updated all relevant tests to fix the usages of the now private
constructor, including:
   1. Removed now obsolete tests (files and cases).
2. Updated all relevant tests to get the iterators and the sentinels via
`begin()` and `end()`, wherever applicable .
   3. Added test cases to confirm that P3059R2 was implemented properly.
   4. Minor other (necessary) tweaks.

---------

Co-authored-by: Hristo Hristov <zingam@outlook.com>
Co-authored-by: A. Jiang <de34@live.cn>

…0 merge (llvm#213062)

Consistency improvements and other small tweaks.

A follow-up to llvm#193891 - the
changes were deferred to reduce the size of an already large and
approved PR.

…0 merge (llvm#213062)

Consistency improvements and other small tweaks.

A follow-up to llvm#193891 - the
changes were deferred to reduce the size of an already large and
approved PR.

)

The previous test was dereferencing `begin()` iterator on empty view
which is UB, because `begin() == end()`.

A new test case was suggested in a post-merge feedback in #193891, which
verifies LWG3568 through constant evaluation. Such a `constexpr`
`basic_istream_view` variable can only be created if it is completely
initialized, including its exposition-only _`value_`_ member.

The existing test case is changed to use a non-empty stream and a
testing class type for which `operator>>` is no-op. The state of the
class object stored in `basic_istream_view` is unchanged even after the
initial `operator>>` call.

This avoids dereferencing a past-the-end iterator while testing LWG3568.

…#215589)

The previous test was dereferencing `begin()` iterator on empty view
which is UB, because `begin() == end()`.

A new test case was suggested in a post-merge feedback in llvm#193891, which
verifies LWG3568 through constant evaluation. Such a `constexpr`
`basic_istream_view` variable can only be created if it is completely
initialized, including its exposition-only _`value_`_ member.

The existing test case is changed to use a non-empty stream and a
testing class type for which `operator>>` is no-op. The state of the
class object stored in `basic_istream_view` is unchanged even after the
initial `operator>>` call.

This avoids dereferencing a past-the-end iterator while testing LWG3568.