Handle magic comments for disabling/enabling with more flexibility

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 * Duplicate imports in a single import list are now eliminated.
 
+* The magic comments for disabling and enabling Ormolu now can encompass any
+  fragment of code provided that the remaining code after exclusion of the
+  disabled part is still syntactically correct. [Issue
+  601](https://github.com/tweag/ormolu/issues/601).
+
 ## Ormolu 0.1.0.0
 
 * Fixed rendering of type signatures concerning several identifiers. [Issue

data/examples/other/disabling/indented-fragment-out.hs

@@ -0,0 +1,7 @@
+foo =
+  {- ORMOLU_DISABLE -}
+  testCase "Foo" testFoo :
+  testCase "Bar" testBar :
+  testCase "Baz" testBaz :
+  {- ORMOLU_ENABLE -}
+  []

data/examples/other/disabling/indented-fragment.hs

@@ -0,0 +1,7 @@
+foo =
+    {- ORMOLU_DISABLE -}
+    testCase "Foo" testFoo :
+    testCase "Bar" testBar :
+    testCase "Baz" testBaz :
+    {- ORMOLU_ENABLE -}
+    []

src/Ormolu/Parser/CommentStream.hs

@@ -27,6 +27,7 @@ import qualified GHC
 import qualified Lexer as GHC
 import Ormolu.Parser.Pragma
 import Ormolu.Parser.Shebang
+import Ormolu.Processing.Common
 import Ormolu.Utils (showOutputable)
 import SrcLoc
 
@@ -109,11 +110,15 @@ mkComment ls (L l s) = (ls', comment)
             Nothing -> s :| []
             Just (x :| xs) ->
               let getIndent y =
-                    if all isSpace y
+                    if all isSpace y || y == endDisabling
                       then startIndent
                       else length (takeWhile isSpace y)
                   n = minimum (startIndent : fmap getIndent xs)
-               in x :| (drop n <$> xs)
+                  removeIndent y =
+                    if y == endDisabling
+                      then y
+                      else drop n y
+               in x :| (removeIndent <$> xs)
           else s :| []
     (atomsBefore, ls') =
       case dropWhile ((< commentLine) . fst) ls of

src/Ormolu/Processing/Common.hs

@@ -20,7 +20,7 @@ data OrmoluState
 
 -- | Marker for the beginning of the region where Ormolu should be disabled.
 startDisabling :: IsString s => s
-startDisabling = "{- ORMOLU_DISABLING_START"
+startDisabling = "{- ORMOLU_DISABLE_START"
 
 -- | Marker for the end of the region where Ormolu should be disabled.
 endDisabling :: IsString s => s

src/Ormolu/Processing/Postprocess.hs

@@ -1,3 +1,5 @@
+{-# LANGUAGE ViewPatterns #-}
+
 -- | Postprocessing for the results of printing.
 module Ormolu.Processing.Postprocess
   ( postprocess,
@@ -17,5 +19,5 @@ postprocess =
     . filter (not . magicComment)
     . T.lines
   where
-    magicComment x =
+    magicComment (T.stripStart -> x) =
       x == startDisabling || x == endDisabling

src/Ormolu/Processing/Preprocess.hs

@@ -143,7 +143,8 @@ magicComment ::
   -- | Whether or not the two strings watch
   Bool
 magicComment expected s0 = isJust $ do
-  s1 <- dropWhile isSpace <$> L.stripPrefix "{-" s0
-  s2 <- dropWhile isSpace <$> L.stripPrefix expected s1
+  let trim = dropWhile isSpace
+  s1 <- trim <$> L.stripPrefix "{-" (trim s0)
+  s2 <- trim <$> L.stripPrefix expected s1
   s3 <- L.stripPrefix "-}" s2
   guard (all isSpace s3)