Add test for T23184
There was an outright bug, which Simon fixed in July 2021, as a little side-fix on a complicated patch:
commit 6656f016
Author: Simon Peyton Jones <simonpj@microsoft.com>
Date: Fri Jul 23 23:57:01 2021 +0100
A bunch of changes related to eta reduction
This is a large collection of changes all relating to eta
reduction, originally triggered by #18993, but there followed
a long saga.
Specifics:
...lots of lines omitted...
Other incidental changes
* Fix a fairly long-standing outright bug in the ApplyToVal case of
GHC.Core.Opt.Simplify.mkDupableContWithDmds. I was failing to take the
tail of 'dmds' in the recursive call, which meant the demands were All
Wrong. I have no idea why this has not caused problems before now.
Note this "Fix a fairly longstanding outright bug". This is the specific fix
@@ -3552,8 +3556,8 @@ mkDupableContWithDmds env dmds
-- let a = ...arg...
-- in [...hole...] a
-- NB: sc_dup /= OkToDup; that is caught earlier by contIsDupable
- do { let (dmd:_) = dmds -- Never fails
- ; (floats1, cont') <- mkDupableContWithDmds env dmds cont
+ do { let (dmd:cont_dmds) = dmds -- Never fails
+ ; (floats1, cont') <- mkDupableContWithDmds env cont_dmds cont
; let env' = env `setInScopeFromF` floats1
; (_, se', arg') <- simplArg env' dup se arg
; (let_floats2, arg'') <- makeTrivial env NotTopLevel dmd (fsLit "karg") arg'
Ticket #23184 (closed) is a report of the bug that this diff fixes.