Desugar RecordUpd in `tcExpr`wip/T18802

This patch typechecks record updates by desugaring them inside
the typechecker using the HsExpansion mechanism, and then typechecking
this desugared result.

Example:

    data T p q = T1 { x :: Int, y :: Bool, z :: Char }
               | T2 { v :: Char }
               | T3 { x :: Int }
               | T4 { p :: Float, y :: Bool, x :: Int }
               | T5

The record update `e { x=e1, y=e2 }` desugars as follows

  e { x=e1, y=e2 }
    ===>
  let { x' = e1; y' = e2 } in
  case e of
     T1 _ _ z -> T1 x' y' z
     T4 p _ _ -> T4 p y' x'

The desugared expression is put into an HsExpansion, and we typecheck
that.

The full details are given in Note [Record Updates] in GHC.Tc.Gen.Expr.

Fixes #2595 #3632 #10808 #10856 #16501 #18311 #18802 #21158 #21289

Updates haddock submodule

1 files changed, 4 insertions, 2 deletions

diff --git a/testsuite/tests/typecheck/should_fail/tcfail102.stderr b/testsuite/tests/typecheck/should_fail/tcfail102.stderr
index fdfedf7ebb..88b01eea0c 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail102.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail102.stderr
@@ -4,10 +4,12 @@ tcfail102.hs:1:14: warning: [-Wdeprecated-flags (in -Wdefault)]
 
 tcfail102.hs:9:7: error:
     • Could not deduce (Integral (Ratio a))
-        arising from a record update
       from the context: Integral a
         bound by the type signature for:
                    f :: forall a. Integral a => P (Ratio a) -> P (Ratio a)
         at tcfail102.hs:8:1-45
-    • In the expression: x {p = p x}
+    • In a record update at field ‘p’,
+      with type constructor ‘P’
+      and data constructor ‘P’.
+      In the expression: x {p = p x}
       In an equation for ‘f’: f x = x {p = p x}