[PATCH] D26596: [RFC] Add _LIBCPP_NO_DISCARD and apply it to `Container::empty()`, `unique_ptr<T>::release()`, and `Lockable::try_lock()`

[Eric Fiselier via cfe-commits]

EricWF updated this revision to Diff 77772.
EricWF added a comment.

Add final touches. This patch is ready to go.

@chandlerc mentioned he would still like to see more per-function granularity for enabling/disabling the libc++ [[nodiscard]] macro in order to ease adoption in large code bases. However I'm concerned about the cost of maintaining 100+ user-visible configuration macros. This current patch attempts to find a happy medium by grouping similar functions  into a single macro; which can be sub-divided further if needed.

As a general rule functions where [[nodiscard]] may yield false positives (ie `unique_ptr::release()`) should always have their own group, since fixing the false-positives is a stylistic change. Functions where a discarded value is always a bug, either for correctness reasons (ie `try_lock()`) or  because the call has no side-effects (ie `string::empty`), may be grouped together as appropriate; Warnings generated by these groups should either be rare or high priority bugs. Dividing groups in this manner attempts to maximize adaptability while being reasonably maintainable.

@mclow.lists Any last words?


https://reviews.llvm.org/D26596

Files:
  docs/UsingLibcxx.rst
  include/__config
  include/__hash_table
  include/__mutex_base
  include/algorithm
  include/deque
  include/ext/hash_map
  include/forward_list
  include/list
  include/locale
  include/map
  include/memory
  include/mutex
  include/regex
  include/set
  include/shared_mutex
  include/string
  include/string_view
  include/thread
  include/unordered_map
  include/unordered_set
  include/vector
  test/libcxx/containers/no-discard-disable.fail.cpp
  test/libcxx/containers/no-discard.fail.cpp
  test/libcxx/test/config.py
  test/libcxx/thread/thread.mutex/try_lock_no_discard.fail.cpp
  test/libcxx/thread/thread.mutex/try_lock_no_discard_disabled.fail.cpp
  test/libcxx/utilities/memory/disable_no_discard_smart_ptr_observers.fail.cpp
  test/libcxx/utilities/memory/no_discard_smart_ptr_observers.fail.cpp
  test/libcxx/utilities/memory/unique.ptr/disable_no_discard_release.fail.cpp
  test/libcxx/utilities/memory/unique.ptr/no_discard_release.fail.cpp
  test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock.pass.cpp
  test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_for.pass.cpp
  test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.locking/try_lock_until.pass.cpp
  test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock.pass.cpp
  test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_for.pass.cpp
  test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.locking/try_lock_until.pass.cpp

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