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Don't fail when rendering an Unbounded layout of a grouped Line #92

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Don't fail when rendering an Unbounded layout of a grouped Line #92

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9 changes: 9 additions & 0 deletions prettyprinter/src/Data/Text/Prettyprint/Doc/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -1535,6 +1535,14 @@ startsWithLine sds = case sds of
SAnnPop s -> startsWithLine s
_ -> False

-- | Test whether a docstream is 'SFail', ignoring any annotations.
isFail :: SimpleDocStream ann -> Bool
isFail sds = case sds of
SFail -> True
SAnnPush _ s -> isFail s
SAnnPop s -> isFail s
_ -> False


-- $
-- >>> import qualified Data.Text.IO as T
Expand Down Expand Up @@ -1794,6 +1802,7 @@ layoutWadlerLeijen
-> SimpleDocStream ann -- ^ Choice B.
-> SimpleDocStream ann -- ^ Choice A if it fits, otherwise B.
selectNicer (FittingPredicate fits) lineIndent currentColumn x y
| isFail x = y
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@sjakobi sjakobi Nov 5, 2019 •
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I was wondering whether we need to worry about SFail appearing elsewhere than the beginning of a left Union branch. At least fuse doesn't seem to "hide" the Fail in a (Union Fail x) though:

https://github.com/quchen/prettyprinter/blob/4d51362d7ea8bca0fe9e7ffec2ccd8fcd0065c0d/prettyprinter/src/Data/Text/Prettyprint/Doc/Internal.hs#L1407

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@quchen quchen Nov 5, 2019

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isFail is False if the document fails, but that’s the same thing the two fitting predicates (for layoutPretty and layoutSmart) yield. What does the explicit isFail clause change?

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@sjakobi sjakobi Nov 5, 2019

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I've explained this in #91 (comment).

The short version is that both fitting predicates shortcut to True when the maxWidth is Nothing – which is the case with Unbounded layout options.

| fits pWidth minNestingLevel availableWidth x = x
| otherwise = y
where
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8 changes: 8 additions & 0 deletions prettyprinter/test/Testsuite/Main.hs
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Expand Up @@ -80,6 +80,8 @@ tests = testGroup "Tests"
, testCase "Preserve leading indentation"
removeTrailingWhitespacePreserveIndentation
]
, testCase "Unbounded layout of `group`ed Line fails (#91)"
regressionUnboundedGroupedLine
]
]

Expand Down Expand Up @@ -296,3 +298,9 @@ removeTrailingWhitespacePreserveIndentation
= let sdoc :: SimpleDocStream ()
sdoc = SLine 2 (SChar 'x' SEmpty)
in assertEqual "" sdoc (removeTrailingWhitespace sdoc)

regressionUnboundedGroupedLine :: Assertion
regressionUnboundedGroupedLine
= let sdoc :: SimpleDocStream ()
sdoc = layoutPretty (LayoutOptions Unbounded) (group hardline)
in assertEqual "" (SLine 0 SEmpty) sdoc