Ben Gamari authored Aug 19, 2019 and Marge Bot committed Nov 08, 2019

When floating a single-alternative case we previously would set the
context level to the level where we were floating the case. However,
this is wrong as we are only moving the case and its binders. This
resulted in #16978, where the disrepancy caused us to
unnecessarily abstract over some free variables of the case body,
resulting in shadowing and consequently Core Lint failures.

(cherry picked from commit a2a0e6f3)