Backoff group optimization

src/Dodo.purs

@@ -386,6 +386,11 @@ print (Printer printer) opts = flip go initState <<< pure <<< Doc
             go (Doc doc1 : LeaveFlexGroup : stk) state
               { flexGroup = FlexGroupOpen
               }
+          FlexGroupOpen | state.position.ribbonWidth > 0 ->
+            go (Doc doc1 : stk) state
+              { flexGroup = FlexGroupReset $ storeState stack state
+              , buffer = Buffer.branch state.buffer
+              }
           _ ->
             go (Doc doc1 : stk) state
         FlexAlt flexDoc doc1 -> case state.flexGroup of

test/snapshots/DodoFlexPrefixOptimization.output

@@ -10,6 +10,7 @@ out: e
 abce
 out: a
 out: b
+out: b
 out: c
 out: d
 abcd
@@ -18,3 +19,17 @@ out: b
 out: c
 out: e
 abce
+out: a
+out: b
+out: c
+out: d
+out: e
+out: b
+out: c
+out: d
+out: e
+out: e
+out: f
+out: g
+* a b c d
+  e f g

test/snapshots/DodoFlexPrefixOptimization.purs

@@ -3,7 +3,7 @@ module DodoFlexPrefixOptimization where
 import Prelude
 
 import Data.Foldable (fold)
-import Dodo (Doc, flexAlt, flexGroup, fourSpaces, plainText, print, text, withPosition)
+import Dodo (Doc, align, flexAlt, flexGroup, fourSpaces, paragraph, plainText, print, text, withPosition)
 import Effect (Effect)
 import Effect.Class.Console as Console
 import Effect.Unsafe (unsafePerformEffect)
@@ -34,9 +34,28 @@ test2 = flexGroup $ fold
       ]
   ]
 
+-- Bad output due to aggressive optimization:
+-- * a
+--   b c d e
+--   f g
+test3 :: forall a. Doc a
+test3 = flexGroup $ text "* " <> align 2 letters
+  where
+  letters =
+    paragraph $ map logText
+      [ "a"
+      , "b"
+      , "c"
+      , "d"
+      , "e"
+      , "f"
+      , "g"
+      ]
+
 main :: Effect Unit
 main = do
   Console.log $ print plainText (fourSpaces { pageWidth = 1 }) test1
   Console.log $ print plainText fourSpaces test1
   Console.log $ print plainText (fourSpaces { pageWidth = 1 }) test2
   Console.log $ print plainText fourSpaces test2
+  Console.log $ print plainText (fourSpaces { pageWidth = 10 }) test3