Build executable with '-threaded' (fixes #399)

2 files changed, 23 insertions, 0 deletions

diff --git a/html-test/src/Threaded.hs b/html-test/src/Threaded.hs
new file mode 100644
index 00000000..7f3073ad
--- /dev/null
+++ b/html-test/src/Threaded.hs
@@ -0,0 +1,10 @@
+{-# LANGUAGE TemplateHaskell #-}
+
+-- | Ensures haddock built with @-threaded@.
+module Threaded where
+
+import Threaded_TH
+
+-- | @$(forkTH)@ fails at compile time if haddock isn't using the
+-- threaded RTS.
+f = $(forkTH)
diff --git a/html-test/src/Threaded_TH.hs b/html-test/src/Threaded_TH.hs
new file mode 100644
index 00000000..53e5a399
--- /dev/null
+++ b/html-test/src/Threaded_TH.hs
@@ -0,0 +1,13 @@
+-- | Imported by 'Threaded', since a TH splice can't be used in the
+-- module where it is defined.
+module Threaded_TH where
+
+import Control.Concurrent (forkOS)
+import Language.Haskell.TH.Syntax (Exp (LitE), Lit (IntegerL), Q, runIO)
+
+-- | forkOS requires the threaded RTS, so this TH fails if haddock was
+-- built without @-threaded@.
+forkTH :: Q Exp
+forkTH = do
+  _ <- runIO (forkOS (return ()))
+  return (LitE (IntegerL 0))