Add werror function to Flavour.hs

This function makes it easy to turn on `-Werror` in the correct manner
to mimic how CI turns on -Werror.

1 files changed, 7 insertions, 1 deletions

diff --git a/hadrian/src/Flavour.hs b/hadrian/src/Flavour.hs
index e95e0d7e1f..23e2aa8a81 100644
--- a/hadrian/src/Flavour.hs
+++ b/hadrian/src/Flavour.hs
@@ -1,4 +1,4 @@
-module Flavour (Flavour (..)) where
+module Flavour (Flavour (..), werror) where
 
 import Expression
 
@@ -32,3 +32,9 @@ data Flavour = Flavour {
     ghcProfiled :: Bool,
     -- | Build GHC with debug information.
     ghcDebugged :: Bool }
+
+
+-- | Turn on -Werror for packages built with the stage1 compiler.
+-- It mimics the CI settings so is useful to turn on when developing.
+werror :: Flavour -> Flavour
+werror fl = fl { args = args fl <> (builder Ghc ? notStage0 ? arg "-Werror") }