Make dataToQa aware of Data instances which use functions to implement toConstr

Trac #10796 exposes a way to make `template-haskell`'s `dataToQa` function
freak out if using a `Data` instance that produces a `Constr` (by means of
`toConstr`) using a function name instead of a data constructor name. While
such `Data` instances are somewhat questionable, they are nevertheless present
in popular libraries (e.g., `containers`), so we can at least make `dataToQa`
aware of their existence.

In order to properly distinguish strings which represent variables (as opposed
to data constructors), it was necessary to move functionality from `Lexeme` (in
`ghc`) to `GHC.Lexeme` in a new `ghc-boot` library (which was previously named
`bin-package-db`).

Reviewed By: goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D1313

GHC Trac Issues: #10796

1 files changed, 15 insertions, 0 deletions

diff --git a/testsuite/tests/th/T10796a.hs b/testsuite/tests/th/T10796a.hs
new file mode 100644
index 0000000000..6c1ac8c78c
--- /dev/null
+++ b/testsuite/tests/th/T10796a.hs
@@ -0,0 +1,15 @@
+{-# LANGUAGE TemplateHaskell #-}
+module T10796a where
+
+import Data.Ratio
+import Data.Set (Set, fromList)
+import Language.Haskell.TH.Syntax (liftData)
+
+-- Data instance with toConstr implemented using a variable,
+-- not a data constructor
+splicedSet :: Set Char
+splicedSet = $(liftData (fromList "test"))
+
+-- Infix data constructor
+splicedRatio :: Ratio Int
+splicedRatio = $(liftData (1 % 2 :: Ratio Int))