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

5 files changed, 5 insertions, 28 deletions

diff --git a/testsuite/tests/patsyn/should_fail/all.T b/testsuite/tests/patsyn/should_fail/all.T
index 2db852a35b..9879f2d9b0 100644
--- a/testsuite/tests/patsyn/should_fail/all.T
+++ b/testsuite/tests/patsyn/should_fail/all.T
@@ -15,7 +15,6 @@ test('records-no-uni-update', normal, compile_fail, [''])
 test('records-no-uni-update2', normal, compile_fail, [''])
 test('records-mixing-fields', normal, compile_fail, [''])
 test('records-exquant', normal, compile_fail, [''])
-test('records-poly-update', normal, compile_fail, [''])
 test('records-nofieldselectors', normal, compile_fail, [''])
 test('mixed-pat-syn-record-sels', normal, compile_fail, [''])
 test('T11039', normal, compile_fail, [''])
diff --git a/testsuite/tests/patsyn/should_fail/records-exquant.stderr b/testsuite/tests/patsyn/should_fail/records-exquant.stderr
index b5c3fddcc3..2f3a0f508b 100644
--- a/testsuite/tests/patsyn/should_fail/records-exquant.stderr
+++ b/testsuite/tests/patsyn/should_fail/records-exquant.stderr
@@ -4,8 +4,3 @@ records-exquant.hs:8:7: error:
     • In the expression: a (Showable True)
       In an equation for ‘qux’: qux = a (Showable True)
     Suggested fix: Use pattern-matching syntax instead
-
-records-exquant.hs:10:7: error:
-    • Record update for insufficiently polymorphic field: a :: a
-    • In the expression: (Showable ()) {a = True}
-      In an equation for ‘foo’: foo = (Showable ()) {a = True}
diff --git a/testsuite/tests/patsyn/should_fail/records-no-uni-update.stderr b/testsuite/tests/patsyn/should_fail/records-no-uni-update.stderr
index 71e2a99407..c7e60f1085 100644
--- a/testsuite/tests/patsyn/should_fail/records-no-uni-update.stderr
+++ b/testsuite/tests/patsyn/should_fail/records-no-uni-update.stderr
@@ -1,5 +1,7 @@
 
 records-no-uni-update.hs:7:7: error:
-    non-bidirectional pattern synonym ‘Uni’ used in an expression
-    In the expression: ("a", "b") {a = "b"}
-    In an equation for ‘foo’: foo = ("a", "b") {a = "b"}
+    • non-bidirectional pattern synonym ‘Uni’ used in an expression
+    • In a record update at field ‘a’
+      and with pattern synonym ‘Uni’.
+      In the expression: ("a", "b") {a = "b"}
+      In an equation for ‘foo’: foo = ("a", "b") {a = "b"}
diff --git a/testsuite/tests/patsyn/should_fail/records-poly-update.hs b/testsuite/tests/patsyn/should_fail/records-poly-update.hs
deleted file mode 100644
index f488b18bc6..0000000000
--- a/testsuite/tests/patsyn/should_fail/records-poly-update.hs
+++ /dev/null
@@ -1,13 +0,0 @@
-{-# LANGUAGE PatternSynonyms #-}
-module Main where
-
-pattern ReqNoProv :: Show a => a -> Maybe a
-pattern ReqNoProv{j} = Just j
-
-data A = A deriving Show
-
-p1 = Just True
-
-p6 = p1 {j = A}
-
-main = print p6
diff --git a/testsuite/tests/patsyn/should_fail/records-poly-update.stderr b/testsuite/tests/patsyn/should_fail/records-poly-update.stderr
deleted file mode 100644
index 44bee9b2c3..0000000000
--- a/testsuite/tests/patsyn/should_fail/records-poly-update.stderr
+++ /dev/null
@@ -1,6 +0,0 @@
-
-records-poly-update.hs:11:14: error:
-    • Couldn't match expected type ‘Bool’ with actual type ‘A’
-    • In the ‘j’ field of a record
-      In the expression: p1 {j = A}
-      In an equation for ‘p6’: p6 = p1 {j = A}