Default build flags available

Stackage/Build.hs

@@ -40,6 +40,7 @@ defaultBuildSettings = BuildSettings
     , cleanBeforeBuild = True
     , excludedPackages = empty
     , testWorkerThreads = 4
+    , flags = Set.fromList $ words "blaze_html_0_5"
     }
 
 build :: BuildSettings -> IO ()

Stackage/InstallInfo.hs

@@ -31,7 +31,7 @@ getInstallInfo settings = do
             | otherwise = stablePackages settings
         allPackages = dropExcluded settings allPackages'
     let totalCore = extraCore settings `Set.union` Set.map (\(PackageIdentifier p _) -> p) (hpcore hp)
-    pdb <- loadPackageDB totalCore allPackages
+    pdb <- loadPackageDB settings totalCore allPackages
     final <- narrowPackageDB pdb $ Set.fromList $ Map.toList $ Map.map snd $ allPackages
 
     putStrLn "Printing build plan to build-plan.log"

Stackage/LoadDatabase.hs

@@ -26,7 +26,8 @@ import           Distribution.PackageDescription       (Condition (..),
                                                         genPackageFlags,
                                                         libBuildInfo,
                                                         packageDescription,
-                                                        testBuildInfo)
+                                                        testBuildInfo,
+                                                        FlagName (FlagName))
 import           Distribution.PackageDescription.Parse (ParseResult (ParseOk),
                                                         parsePackageDescription)
 import           Distribution.System                   (buildArch, buildOS)
@@ -46,10 +47,11 @@ import           Stackage.Util
 -- version.
 --
 -- * For other packages, select the maximum version number.
-loadPackageDB :: Set PackageName -- ^ core packages
+loadPackageDB :: BuildSettings
+              -> Set PackageName -- ^ core packages
               -> Map PackageName (VersionRange, Maintainer) -- ^ additional deps
               -> IO PackageDB
-loadPackageDB core deps = do
+loadPackageDB settings core deps = do
     tarName <- getTarballName
     lbs <- L.readFile tarName
     addEntries mempty $ Tar.read lbs
@@ -119,4 +121,5 @@ loadPackageDB core deps = do
             checkCond' (COr c1 c2) = checkCond' c1 || checkCond' c2
             checkCond' (CAnd c1 c2) = checkCond' c1 && checkCond' c2
 
-            flags = map flagName $ filter flagDefault $ genPackageFlags gpd
+            flags = map flagName (filter flagDefault $ genPackageFlags gpd) ++
+                    (map FlagName $ Set.toList $ Stackage.Types.flags settings)

Stackage/Types.hs

@@ -79,4 +79,6 @@ data BuildSettings = BuildSettings
     -- packages are dependencies of others, they will still be included.
     , testWorkerThreads      :: Int
     -- ^ How many threads to spawn for running test suites.
+    , flags                  :: Set String
+    -- ^ Compile flags which should be turned on.
     }