PmCheck: Handle ⊥ and strict fields correctly (#18341)wip/T18341

In #18341, we discovered an incorrect digression from Lower Your Guards.
This MR changes what's necessary to support properly fixing #18341.

In particular, bottomness constraints are now properly tracked in the
oracle/inhabitation testing, as an additional field
`vi_bot :: Maybe Bool` in `VarInfo`. That in turn allows us to
model newtypes as advertised in the Appendix of LYG and fix #17725.
Proper handling of ⊥ also fixes #17977 (once again) and fixes #18670.

For some reason I couldn't follow, this also fixes #18273.

I also added a couple of regression tests that were missing. Most of
them were already fixed before.

In summary, this patch fixes #18341, #17725, #18273, #17977 and #18670.

Metric Decrease:
    T12227

1 files changed, 3 insertions, 3 deletions

diff --git a/compiler/GHC/Tc/Types.hs b/compiler/GHC/Tc/Types.hs
index 5111dbbe3d..0af8bbb2a4 100644
--- a/compiler/GHC/Tc/Types.hs
+++ b/compiler/GHC/Tc/Types.hs
@@ -106,7 +106,7 @@ import GHC.Tc.Types.Origin
 import GHC.Types.Annotations
 import GHC.Core.InstEnv
 import GHC.Core.FamInstEnv
-import {-# SOURCE #-} GHC.HsToCore.PmCheck.Types (Deltas)
+import {-# SOURCE #-} GHC.HsToCore.PmCheck.Types (Nablas)
 import GHC.Data.IOEnv
 import GHC.Types.Name.Reader
 import GHC.Types.Name
@@ -324,9 +324,9 @@ data DsLclEnv = DsLclEnv {
         dsl_loc     :: RealSrcSpan,      -- To put in pattern-matching error msgs
 
         -- See Note [Note [Long-distance information] in "GHC.HsToCore.PmCheck"
-        -- The set of reaching values Deltas is augmented as we walk inwards,
+        -- The set of reaching values Nablas is augmented as we walk inwards,
         -- refined through each pattern match in turn
-        dsl_deltas  :: Deltas
+        dsl_nablas  :: Nablas
      }
 
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