tree cef18b496ec6a28b6c41d270b8dbc5394d518b99
parent 3d5d4a3683d87847208682adc6a8804497444655
author Doug Gregor <dgregor@apple.com> 1488524590 -0800
committer Doug Gregor <dgregor@apple.com> 1488560145 -0800

[SR-3917] Allow missing witnesses for optional and unavailable requirements.

This is a bit of a hack to dodge an assertion. In essence, it's a
harmless hack, but we'd like to make the handling of optional and
unavailable requirements more rigorous.

(cherry picked from commit 3246b728bdf70fb71e404b059d8fbde66bc14618)