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Alternative fix for #205 #283

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a5342e4
Add performance test for #205
sjakobi Dec 5, 2025
c584f60
Fix layoutSmart regression from blank-line indentation
sjakobi Mar 30, 2026
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58 changes: 46 additions & 12 deletions prettyprinter/src/Prettyprinter/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -1895,6 +1895,7 @@
-> SimpleDocStream ann
layoutPretty (LayoutOptions pageWidth_@(AvailablePerLine lineLength ribbonFraction)) =
layoutWadlerLeijen
smartLine
(FittingPredicate
(\lineIndent currentColumn _initialIndentY sdoc ->
fits
Expand Down Expand Up @@ -1982,7 +1983,8 @@
-> Doc ann
-> SimpleDocStream ann
layoutSmart (LayoutOptions pageWidth_@(AvailablePerLine lineLength ribbonFraction)) =
layoutWadlerLeijen (FittingPredicate fits) pageWidth_
dropIndentationOnEmptyLines .
layoutWadlerLeijen plainLine (FittingPredicate fits) pageWidth_
where
-- Why doesn't layoutSmart simply check the entire document?
--
Expand All @@ -2001,7 +2003,14 @@
go w (SChar _ x) = go (w - 1) x
go w (SText l _t x) = go (w - l) x
go _ (SLine i x)
| minNestingLevel < i = go (lineLength - i) x -- TODO: Take ribbon width into account?! (#142)
| minNestingLevel < i =
let i' = case x of
SEmpty -> 0
SLine{} -> 0
_ -> i
in if minNestingLevel < i'

Check warning on line 2011 in prettyprinter/src/Prettyprinter/Internal.hs

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GitHub Actions / hlint 

Warning in layoutSmart in module Prettyprinter.Internal: Redundant if ▫︎ Found: "if minNestingLevel < i' then go (lineLength - i') x else True" ▫︎ Perhaps: "(not (minNestingLevel < i') || go (lineLength - i') x)"
then go (lineLength - i') x -- TODO: Take ribbon width into account?! (#142)
else True
| otherwise = True
go w (SAnnPush _ x) = go w x
go w (SAnnPop x) = go w x
Expand Down Expand Up @@ -2029,6 +2038,7 @@
layoutUnbounded :: Doc ann -> SimpleDocStream ann
layoutUnbounded =
layoutWadlerLeijen
smartLine
(FittingPredicate
(\_lineIndent _currentColumn _initialIndentY sdoc -> not (failsOnFirstLine sdoc)))
Unbounded
Expand All @@ -2046,13 +2056,45 @@
SAnnPush _ s -> go s
SAnnPop s -> go s

plainLine :: Int -> SimpleDocStream ann -> SimpleDocStream ann
plainLine i x = SLine i x

smartLine :: Int -> SimpleDocStream ann -> SimpleDocStream ann
smartLine i x =
let i' = case x of
SEmpty -> 0
SLine{} -> 0
_ -> i
in SLine i' x

-- | Remove indentation that would otherwise survive on empty lines.
dropIndentationOnEmptyLines :: SimpleDocStream ann -> SimpleDocStream ann
dropIndentationOnEmptyLines = go
where
go sds = case sds of
SFail -> SFail
SEmpty -> SEmpty
SChar c x -> SChar c (go x)
SText l t x -> SText l t (go x)
SLine i x ->
let x' = go x
i' = case x' of
SEmpty -> 0
SLine{} -> 0
_ -> i
in SLine i' x'
SAnnPush ann x -> SAnnPush ann (go x)
SAnnPop x -> SAnnPop (go x)

-- | The Wadler/Leijen layout algorithm
layoutWadlerLeijen
:: forall ann. FittingPredicate ann
:: forall ann. (Int -> SimpleDocStream ann -> SimpleDocStream ann)
-> FittingPredicate ann
-> PageWidth
-> Doc ann
-> SimpleDocStream ann
layoutWadlerLeijen
mkLine
(FittingPredicate fits)
pageWidth_
doc
Expand All @@ -2073,15 +2115,7 @@
Empty -> best nl cc ds
Char c -> let !cc' = cc+1 in SChar c (best nl cc' ds)
Text l t -> let !cc' = cc+l in SText l t (best nl cc' ds)
Line -> let x = best i i ds
-- Don't produce indentation if there's no
-- following text on the same line.
-- This prevents trailing whitespace.
i' = case x of
SEmpty -> 0
SLine{} -> 0
_ -> i
in SLine i' x
Line -> mkLine i (best i i ds)
FlatAlt x _ -> best nl cc (Cons i x ds)
Cat x y -> best nl cc (Cons i x (Cons i y ds))
Nest j x -> let !ij = i+j in best nl cc (Cons ij x ds)
Expand Down
10 changes: 10 additions & 0 deletions prettyprinter/test/Testsuite/Main.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,8 @@ tests = testGroup "Tests"
groupingPerformance
, testCase "fillSep performance"
fillSepPerformance
, testCase "Issue 205"
issue205
]
, testGroup "Regression tests"
[ testCase "layoutSmart: softline behaves like a newline (#49)"
Expand Down Expand Up @@ -285,6 +287,14 @@ fillSepPerformance = docPerformanceTest (pathological 1000)
pathological :: Int -> Doc ann
pathological n = iterate (\x -> fillSep ["a", x <+> "b"] ) "foobar" !! n

issue205 :: Assertion
issue205 = do
let doc = fillSep (replicate 30 (sep ["abc", "xyz" :: Doc ()]))
t = renderStrict (layoutSmart defaultLayoutOptions doc)
timeout 1000000 (evaluate t) >>= \t' -> case t' of
Nothing -> assertFailure "Timeout!"
Just _success -> pure ()

regressionLayoutSmartSoftline :: Assertion
regressionLayoutSmartSoftline
= let doc = "a" <> softline <> "b"
Expand Down
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