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, 29 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_fail/T21158.stderr b/testsuite/tests/typecheck/should_fail/T21158.stderr
new file mode 100644
index 0000000000..88394ad2e9
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T21158.stderr
@@ -0,0 +1,29 @@
+
+T21158.hs:12:14: error:
+    • Couldn't match type: F b0
+                     with: F b
+      Expected: [F b]
+        Actual: [F b0]
+      NB: ‘F’ is a non-injective type family
+      The type variable ‘b0’ is ambiguous
+    • In a record update at field ‘x’,
+      with type constructor ‘T’
+      and data constructor ‘MkT’.
+      In the expression: emptyT {x = newx}
+      In an equation for ‘foo1’: foo1 newx = emptyT {x = newx}
+    • Relevant bindings include
+        foo1 :: [Int] -> T b (bound at T21158.hs:12:1)
+
+T21158.hs:15:49: error:
+    • Couldn't match type: F b1
+                     with: F b
+      Expected: [F b]
+        Actual: [F b1]
+      NB: ‘F’ is a non-injective type family
+      The type variable ‘b1’ is ambiguous
+    • In the second argument of ‘MkT’, namely ‘y’
+      In the expression: MkT newx y
+      In a case alternative: MkT x y -> MkT newx y
+    • Relevant bindings include
+        y :: [F b1] (bound at T21158.hs:15:35)
+        foo2 :: [Int] -> T b (bound at T21158.hs:15:1)