Rework Template Haskell's handling of strictness

Currently, Template Haskell's treatment of strictness is not enough to
cover all possible combinations of unpackedness and strictness. In
addition, it isn't equipped to deal with new features (such as
`-XStrictData`) which can change a datatype's fields' strictness during
compilation.

To address this, I replaced TH's `Strict` datatype with
`SourceUnpackedness` and `SourceStrictness` (which give the programmer a
more complete toolkit to configure a datatype field's strictness than
just `IsStrict`, `IsLazy`, and `Unpack`). I also added the ability to
reify a constructor fields' strictness post-compilation through the
`reifyConStrictness` function.

Fixes #10697.

Test Plan: ./validate

Reviewers: simonpj, goldfire, bgamari, austin

Reviewed By: goldfire, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1603

GHC Trac Issues: #10697

1 files changed, 11 insertions, 0 deletions

diff --git a/testsuite/tests/th/T10697_decided_2.hs b/testsuite/tests/th/T10697_decided_2.hs
new file mode 100644
index 0000000000..241cec3d38
--- /dev/null
+++ b/testsuite/tests/th/T10697_decided_2.hs
@@ -0,0 +1,11 @@
+{-# LANGUAGE TemplateHaskell #-}
+module Main where
+
+import Language.Haskell.TH
+
+data T = T {-# UNPACK #-} !Int !Int Int
+
+$(return [])
+
+main :: IO ()
+main = putStrLn $(reifyConStrictness 'T >>= stringE . show)