From f1dd5c4be6065bedc8cd764767b7c05420a9d40d Mon Sep 17 00:00:00 2001
From: Jasper Van der Jeugt <m@jaspervdj.be>
Date: Tue, 5 Jul 2016 15:21:44 +0200
Subject: Fix error in overlapping blocks

---
 lib/Language/Haskell/Stylish/Block.hs  | 11 ++++++++---
 lib/Language/Haskell/Stylish/Editor.hs |  9 ++++++++-
 2 files changed, 16 insertions(+), 4 deletions(-)

(limited to 'lib')

diff --git a/lib/Language/Haskell/Stylish/Block.hs b/lib/Language/Haskell/Stylish/Block.hs
index fd680a8..d4cca7d 100644
--- a/lib/Language/Haskell/Stylish/Block.hs
+++ b/lib/Language/Haskell/Stylish/Block.hs
@@ -16,6 +16,7 @@ module Language.Haskell.Stylish.Block
 
 --------------------------------------------------------------------------------
 import           Control.Arrow                   (arr, (&&&), (>>>))
+import qualified Data.IntSet                     as IS
 import qualified Language.Haskell.Exts.Annotated as H
 
 
@@ -73,10 +74,14 @@ merge (Block s1 e1) (Block s2 e2) = Block (min s1 s2) (max e1 e2)
 
 --------------------------------------------------------------------------------
 overlapping :: [Block a] -> Bool
-overlapping blocks =
-    any (uncurry overlapping') $ zip blocks (drop 1 blocks)
+overlapping = go IS.empty
   where
-    overlapping' (Block _ e1) (Block s2 _) = e1 >= s2
+    go _   []       = False
+    go acc (b : bs) =
+        let ints = [blockStart b .. blockEnd b] in
+        if any (`IS.member` acc) ints
+            then True
+            else go (IS.union acc $ IS.fromList ints) bs
 
 
 --------------------------------------------------------------------------------
diff --git a/lib/Language/Haskell/Stylish/Editor.hs b/lib/Language/Haskell/Stylish/Editor.hs
index 5d5a864..24d0a94 100644
--- a/lib/Language/Haskell/Stylish/Editor.hs
+++ b/lib/Language/Haskell/Stylish/Editor.hs
@@ -18,6 +18,10 @@ module Language.Haskell.Stylish.Editor
     ) where
 
 
+--------------------------------------------------------------------------------
+import           Data.List                      (intercalate)
+
+
 --------------------------------------------------------------------------------
 import           Language.Haskell.Stylish.Block
 
@@ -40,11 +44,14 @@ applyChanges :: [Change a] -> [a] -> [a]
 applyChanges changes
     | overlapping blocks = error $
         "Language.Haskell.Stylish.Editor.applyChanges: " ++
-        "refusing to make overlapping changes"
+        "refusing to make overlapping changes on lines " ++
+        intercalate ", " (map printBlock blocks)
     | otherwise          = go 1 changes
   where
     blocks = map changeBlock changes
 
+    printBlock b = show (blockStart b) ++ "-" ++ show (blockEnd b)
+
     go _ []                ls = ls
     go n (ch : chs) ls =
         -- Divide the remaining lines into:
-- 
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