From e20ea864fefdb89f1a2f6af9588135c173d58b5d Mon Sep 17 00:00:00 2001
From: Michael Snoyman <michael@snoyman.com>
Date: Tue, 18 Aug 2015 20:09:37 +0300
Subject: [PATCH 1/2] Fix haddock executable name

---
 src/Stack/Build/Haddock.hs  | 2 +-
 src/Stack/Types/Compiler.hs | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/Stack/Build/Haddock.hs b/src/Stack/Build/Haddock.hs
index 7c2e67eb58..b8418f202e 100644
--- a/src/Stack/Build/Haddock.hs
+++ b/src/Stack/Build/Haddock.hs
@@ -203,7 +203,7 @@ generateHaddockIndex descr envOverride wc packageIDs docRelDir destDir = do
                    readProcessNull
                        (Just destDir)
                        envOverride
-                       (compilerExeName wc)
+                       (haddockExeName wc)
                        (["--gen-contents", "--gen-index"] ++ concatMap fst interfaceOpts)
   where
     toInterfaceOpt pid@(PackageIdentifier name _) = do
diff --git a/src/Stack/Types/Compiler.hs b/src/Stack/Types/Compiler.hs
index 9e76fbc1ac..51101c8cd0 100644
--- a/src/Stack/Types/Compiler.hs
+++ b/src/Stack/Types/Compiler.hs
@@ -75,3 +75,7 @@ isWantedCompiler _ _ _ = False
 compilerExeName :: WhichCompiler -> String
 compilerExeName Ghc = "ghc"
 compilerExeName Ghcjs = "ghcjs"
+
+haddockExeName :: WhichCompiler -> String
+haddockExeName Ghc = "haddock"
+haddockExeName Ghcjs = "haddock-ghcjs"

From 4cbca17246a457e740c937522b40382b20422cc5 Mon Sep 17 00:00:00 2001
From: Michael Snoyman <michael@snoyman.com>
Date: Wed, 19 Aug 2015 08:18:45 +0300
Subject: [PATCH 2/2] More fine grained recompile checking

---
 src/Stack/Build/ConstructPlan.hs | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/Stack/Build/ConstructPlan.hs b/src/Stack/Build/ConstructPlan.hs
index 5b3b2f3e4d..5fcdf0738d 100644
--- a/src/Stack/Build/ConstructPlan.hs
+++ b/src/Stack/Build/ConstructPlan.hs
@@ -445,7 +445,7 @@ checkDirtiness ps installed package present wanted = do
             case moldOpts of
                 Nothing -> Just "old configure information not found"
                 Just oldOpts
-                    | oldOpts /= wantConfigCache -> Just $ describeConfigDiff oldOpts wantConfigCache
+                    | Just reason <- describeConfigDiff oldOpts wantConfigCache -> Just reason
                     | psDirty ps -> Just "local file changes"
                     | otherwise -> Nothing
     case mreason of
@@ -454,19 +454,20 @@ checkDirtiness ps installed package present wanted = do
             tell mempty { wDirty = Map.singleton (packageName package) reason }
             return True
 
-describeConfigDiff :: ConfigCache -> ConfigCache -> Text
+describeConfigDiff :: ConfigCache -> ConfigCache -> Maybe Text
 describeConfigDiff old new
-    | configCacheDeps old /= configCacheDeps new = "dependencies changed"
-    | configCacheComponents old /= configCacheComponents new = "components changed"
-    | configCacheHaddock old && not (configCacheHaddock new) = "no longer building haddocks"
-    | not (configCacheHaddock old) && configCacheHaddock new = "building haddocks"
-    | oldOpts /= newOpts = T.pack $ concat
+    | configCacheDeps old /= configCacheDeps new = Just "dependencies changed"
+    | not $ Set.null newComponents =
+        Just $ "components added: " `T.append` T.intercalate ", "
+            (map (decodeUtf8With lenientDecode) (Set.toList newComponents))
+    | not (configCacheHaddock old) && configCacheHaddock new = Just "rebuilding with haddocks"
+    | oldOpts /= newOpts = Just $ T.pack $ concat
         [ "flags changed from "
         , show oldOpts
         , " to "
         , show newOpts
         ]
-    | otherwise = "unknown config cache difference"
+    | otherwise = Nothing
   where
     -- options set by stack
     isStackOpt t = any (`T.isPrefixOf` t)
@@ -487,6 +488,8 @@ describeConfigDiff old new
         | x == y = removeMatching xs ys
     removeMatching xs ys = (xs, ys)
 
+    newComponents = configCacheComponents new `Set.difference` configCacheComponents old
+
 psDirty :: PackageSource -> Bool
 psDirty (PSLocal lp) = lpDirtyFiles lp
 psDirty (PSUpstream _ _ _) = False -- files never change in an upstream package