Enabling -Werror=compat in the testsuite allows us to easily see the
impact that a new warning has on code. It also means that in the period
between adding the warning and making the actual breaking change, all
new test cases that are being added to the testsuite will be
forwards-compatible. This is good because it will make the actual
breaking change contain less irrelevant testsuite updates.
Things that -Wcompat warns about are things that are going to break in
the future, so we can be proactive and keep our testsuite
This patch consists of two main changes:
* Add `TEST_HC_OPTS += -Werror=compat` to the testsuite configuration.
* Fix all broken test cases.
Test Plan: Validate
Reviewers: hvr, goldfire, bgamari, simonpj, RyanGlScott
Reviewed By: goldfire, RyanGlScott
Subscribers: rwbarton, carter
GHC Trac Issues: #15278
Differential Revision: https://phabricator.haskell.org/D5200