[PATCH] D32515: [libcxx] [test] Changes to accommodate LWG 2904 "Make variant move-assignment more exception safe"

[Casey Carter via Phabricator via cfe-commits]

CaseyCarter created this revision.

NOTE: TEST CHANGES ONLY.

These tests will not pass with the current implementation of `variant`, but should give the implementor of LWG2904 a head start.

Details:

test/std/utilities/variant/variant.variant/variant.assign/copy.pass.cpp:

- Make `CopyAssign`'s move operations noexcept so uses in variants continue to prefer copy-and-move over direct construction.
- Fix `makeEmpty`: Copy assignment syntax no longer invokes `MakeEmptyT`'s throwing move constructor, move assignment syntax still does.
- `test_copy_assignment_sfinae`: `variant<int, CopyOnly>` is now copy assignable.
- `test_copy_assignment_different_index`:
  - `CopyThrows` and `MoveThrows` have potentially-throwing move construction, so they are now copy constructed directly into variants instead of via indirect copy-and-move.
  - implement new `CopyCannotThrow` and verify that direct copy construction of such in variants is preferred over indirect copy-and-move when neither method throws.

test/std/utilities/variant/variant.variant/variant.assign/move.pass.cpp:

- `test_move_assignment_sfinae`: `variant<int, MoveOnly>` is now move assignable.

test/std/utilities/variant/variant.variant/variant.assign/T.pass.cpp:

- `test_T_assignment_performs_construction`:
  - assigning `ThrowsCtorT` into a variant now constructs a temporary and moves into the variant; the variant keeps its old value if the temporary construction throws.
  - test that direct construction is preferred to temporary-and-move when neither can throw.
  - test that direct construction is preferred to temporary-and-move when both can throw.

test/support/variant_test_helpers.hpp:
test/std/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp:
test/std/utilities/variant/variant.variant/variant.ctor/move.pass.cpp:

- Fix `makeEmpty`: Copy assignment syntax no longer invokes `MakeEmptyT`'s throwing move constructor, move assignment syntax still does.


https://reviews.llvm.org/D32515

Files:
  test/std/utilities/variant/variant.variant/variant.assign/T.pass.cpp
  test/std/utilities/variant/variant.variant/variant.assign/copy.pass.cpp
  test/std/utilities/variant/variant.variant/variant.assign/move.pass.cpp
  test/std/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp
  test/std/utilities/variant/variant.variant/variant.ctor/move.pass.cpp
  test/support/variant_test_helpers.hpp

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