init: add ignored packages as commented in config

Packages which are not compatible with the resolver are added to the
config but commented out.

See commercialhaskell#1621

src/Stack/Init.hs

@@ -19,6 +19,7 @@ import           Control.Monad.Reader            (MonadReader)
 import           Control.Monad.Trans.Control     (MonadBaseControl)
 import qualified Data.ByteString.Builder         as B
 import qualified Data.ByteString.Lazy            as L
+import qualified Data.ByteString.Char8           as BC
 import qualified Data.HashMap.Strict             as HM
 import qualified Data.IntMap                     as IntMap
 import qualified Data.Foldable                   as F
@@ -95,16 +96,19 @@ initProject currDir initOpts = do
             , projectCompiler = Nothing
             , projectExtraPackageDBs = []
             }
+
+        makeRel dir =
+            case stripDir currDir dir of
+                Nothing
+                    | currDir == dir -> "."
+                    | otherwise -> assert False $ toFilePath dir
+                Just rel -> toFilePath rel
+
         pkgs = map toPkg $ Map.elems (fmap fst rbundle)
         toPkg dir = PackageEntry
             { peValidWanted = Nothing
             , peExtraDepMaybe = Nothing
-            , peLocation = PLFilePath $
-                case stripDir currDir dir of
-                    Nothing
-                        | currDir == dir -> "."
-                        | otherwise -> assert False $ toFilePath dir
-                    Just rel -> toFilePath rel
+            , peLocation = PLFilePath $ makeRel dir
             , peSubdirs = []
             }
 
@@ -128,18 +132,21 @@ initProject currDir initOpts = do
         (if exists then "Overwriting existing configuration file: "
          else "Writing configuration to file: ")
         <> T.pack reldest
-    liftIO $ L.writeFile dest' $ B.toLazyByteString $ renderStackYaml p
+    liftIO $ L.writeFile dest'
+           $ B.toLazyByteString
+           $ renderStackYaml p (Map.elems $ fmap (makeRel . fst) ignored)
     $logInfo "All done."
 
 -- | Render a stack.yaml file with comments, see:
 -- https://github.com/commercialhaskell/stack/issues/226
-renderStackYaml :: Project -> B.Builder
-renderStackYaml p =
+renderStackYaml :: Project -> [FilePath]-> B.Builder
+renderStackYaml p ignoredPackages =
     case Yaml.toJSON p of
         Yaml.Object o -> renderObject o
         _ -> assert False $ B.byteString $ Yaml.encode p
   where
     renderObject o =
+        B.byteString "# This file was automatically generated by stack init\n" <>
         B.byteString "# For more information, see: http://docs.haskellstack.org/en/stable/yaml_configuration.html\n\n" <>
         F.foldMap (goComment o) comments <>
         goOthers (o `HM.difference` HM.fromList comments) <>
@@ -158,9 +165,15 @@ renderStackYaml p =
             \# Allow a newer minor version of GHC than the snapshot specifies\n\
             \# compiler-check: newer-minor\n"
 
+    ignoredPackagesComment =
+        if ignoredPackages /= [] then
+            "\n# Some packages were found to be incompatible with the resolver and \
+            \have been commented out"
+        else ""
+
     comments =
         [ ("resolver", "Specifies the GHC version and set of packages available (e.g., lts-3.5, nightly-2015-09-21, ghc-7.10.2)")
-        , ("packages", "Local packages, usually specified by relative directory name")
+        , ("packages", "Local packages, usually specified by relative directory name" <> ignoredPackagesComment)
         , ("extra-deps", "Packages to be pulled from upstream that are not in the resolver (e.g., acme-missiles-0.3)")
         , ("flags", "Override default flag values for local packages and extra-deps")
         , ("extra-package-dbs", "Extra package databases containing global packages")
@@ -174,6 +187,11 @@ renderStackYaml p =
                 B.byteString comment <>
                 B.byteString "\n" <>
                 B.byteString (Yaml.encode $ Yaml.object [(name, v)]) <>
+                if (name == "packages") then
+                    B.byteString $ BC.pack $ concat
+                        $ (map (\x -> "#- " ++ x ++ "\n")
+                               ignoredPackages) ++ ["\n"]
+                else "" <>
                 B.byteString "\n"
 
     goOthers o