Refactor part of the renamer to fix Trac #3901
This one was bigger than I anticipated! The problem was that were
were gathering the binders from a pattern before renaming -- but with
record wild-cards we don't know what variables are bound by C {..}
until after the renamer has filled in the "..".
So this patch does the following
* Change all the collect-X-Binders functions in HsUtils so that
they expect to only be called *after* renaming. That means they
don't need to return [Located id] but just [id]. Which turned out
to be a very worthwhile simplification all by itself.
* Refactor the renamer, and in ptic RnExpr.rnStmt, so that it
doesn't need to use collectLStmtsBinders on pre-renamed Stmts.
* This in turn required me to understand how GroupStmt and
TransformStmts were renamed. Quite fiddly. I rewrote most of it;
result is much shorter.
* In doing so I flattened HsExpr.GroupByClause into its parent
GroupStmt, with trivial knock-on effects in other files.
Blargh.
17 files changed: