Changelog - Boost.Outcome documentation

# Changelog

## v2.1.1 XXth July 2019 (Boost 1.71) [release]

### Enhancements:

#184
  As per request from Boost release managers, relocated `version.hpp` and `revision.hpp` into detail, and added the Boost licence boilerplate to the top of every source file which was missing one (I think). Also took the opportunity to run the licence restamping script over all Outcome, so copyright dates are now up to date.
#185
  Add FAQ item explaining issue #185, and why we will do nothing to fix it right now.
#189
  Refactored the `BOOST_OUTCOME_TRY` implementation to use more clarified customisation points capable of accepting very foreign inputs. Removed the `std::experimental::expected<T, E>` specialisations, as those are no longer necessary. Fixed the documentation for the customisation points which previously claimed that they are ADL discovered, which they are not. Added a recipe describing how to add in support for foreign input types.
#183
  Added a separate `motivation/plug_error_code` specifically for Boost.

### Bug fixes:

-
  `BOOST_OUTCOME_VERSION_MINOR` hadn’t been updated to 1.
#181
  Fix issue #181 where Outcome didn’t actually implement the strong swap guarantee, despite being documented as doing so.
#190
  Fix issue #190 in Boost edition where unit test suite was not runnable from the Boost release distro.
#182
  Fix issue #182 where `trait::is_exception_ptr_available<T>` was always true, thus causing much weirdness, like not printing diagnostics and trying to feed everything to `make_exception_ptr()`.
#194
  Fix issue #192 where the `std::basic_outcome_failure_exception_from_error()` was being defined twice for translation units which combine standalone and Boost Outcome’s.

## v2.1 12th Apr 2019 (Boost 1.70) [release]

- #180

  - `success()` and `failure()` now produce types marked `[[nodiscard]]`.

- `include/outcome/outcome.natvis` is now namespace permuted like the rest of Outcome, so debugging Outcome based code in Visual Studio should look much prettier than before.

- #162

  - `.has_failure()` was returning false at times when it should have returned true.

- #152

  - GCC 5 no longer can compile Outcome at all due to https://stackoverflow.com/questions/45607450/gcc5-nested-variable-template-is-not-a-function-template. Added explicit version trap for GCC 5 to say it can not work. Note this is not a breaking change, GCC 5 was never supported officially in any v2 Outcome.

- #150

  - BREAKING CHANGE `result<T, E>`, `boost_result<T, E>` and `std_result<T, E>` no longer implement hard UB on fetching a value from a valueless instance if `E` is a UDT, they now fail to compile with a useful error message. If you wish hard UB, use `unchecked<T, E>`, `boost_unchecked<T, E>` or `std_unchecked<T, E>` instead.

- #140

  - Fixed a nasty corner case bug where value type’s without a copy constructor but with a move constructor would indicate via traits that copy construction was available. Thanks to Microsoft’s compiler team for reporting this issue.

- Added experimental `status_result` and `status_outcome` based on experimental `status_code`.

- Boost edition is now 100% Boost, so defaults for `result` and `outcome` are `boost::system::error_code::errc_t` and `boost::exception_ptr`. Moreover, the test suite in the Boost edition now exclusively tests the Boost edition. One can, of course, freely use the standalone edition with Boost, and the Boost edition with `std` types.

- Renamed ADL discovered customisation point `throw_as_system_error_with_payload()` to `outcome_throw_as_system_error_with_payload()`.

- #135

  - Added much clearer compile failure when user tries `result<T, T>` or `outcome` where two or more types are identical. Thanks to Andrzej Krzemieński for suggesting a technique which combines SFINAE correctness with the remaining ability for `result<T, T>` etc to be a valid type, but not constructible.

- #67

  - Fixed one of the oldest long open bugs in Outcome, that the noexcept unit tests failed on OS X for an unknown reason.

- #115

  - Outcome did not construct correctly from `failure_type`.

- Inexplicably outcome’s error + exception constructor had been removed. Nobody noticed during the Boost peer review, which is worrying seeing as that constructor is needed for one of the main advertised features to Boost!

- #107 and #116

  - `operator==` and `operator!=` now become disabled if the value, error and exception types do not implement the same operator.
  - Relatedly, both comparison operators simply didn’t work right. Fixed.

- #109

  - `swap()` now has correct `noexcept` calculation and now correctly orders the swaps to be whichever is the throwing swap first.

- Added reference dump of v2.1 ABI so we can check if ABI breakage detection works in the next set of changes, plus Travis job to check ABI and API compatibility per commit.

- #124

  - `BOOST_OUTCOME_TRY` is now overloaded and selects `void` or `auto` edition according to input parameter count.

- #120

  - Fix generation of double underscored temporary variables in `BOOST_OUTCOME_UNIQUE_NAME`, which is UB.

- #110

  - Separated `result` from its hard coded dependency on the `<system_error>` header.
  - Renamed `result` and `outcome` to `basic_result` and `basic_outcome`.
  - Renamed `result.hpp` into `basic_result.hpp`.
  - Moved `<system_error>` and `<exception>` dependent code into new `std_result.hpp` and `std_outcome.hpp` header files.
  - Added `boost_result.hpp` and `boost_outcome.hpp` which use Boost.System and Boost.Exception (these are `result.hpp` and `outcome.hpp` in the Boost edition).

## v2.0 18th Jan 2018 [release]

- Boost peer review edition. This is what was reviewed.
- Changelog from v1 can be found in the release notes for this release.

Last revised: June 25, 2019 at 17:01:21 +0100