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|
--------------------------------------------------------------------------------
-- | This module is useful for aligning things.
module Language.Haskell.Stylish.Align
( Alignable (..)
, align
) where
--------------------------------------------------------------------------------
import Data.List (nub)
import qualified Language.Haskell.Exts as H
--------------------------------------------------------------------------------
import Language.Haskell.Stylish.Editor
import Language.Haskell.Stylish.Util
--------------------------------------------------------------------------------
-- | This represent a single line which can be aligned. We have something on
-- the left and the right side, e.g.:
--
-- > [x] -> x + 1
-- > ^^^^ ^^^^^
-- > LEFT RIGHT
--
-- We also have the container which holds the entire line:
--
-- > [x] -> x + 1
-- > ^^^^^^^^^^^^^
-- > CONTAINER
--
-- And then we have a "right lead" which is just represented by an 'Int', since
-- @haskell-src-exts@ often does not allow us to access it. In the example this
-- is:
--
-- > [x] -> x + 1
-- > ^^^
-- > RLEAD
--
-- This info is enough to align a bunch of these lines. Users of this module
-- should construct a list of 'Alignable's representing whatever they want to
-- align, and then call 'align' on that.
data Alignable a = Alignable
{ aContainer :: !a
, aLeft :: !a
, aRight :: !a
-- | This is the minimal number of columns we need for the leading part not
-- included in our right string. For example, for datatype alignment, this
-- leading part is the string ":: " so we use 3.
, aRightLead :: !Int
} deriving (Show)
--------------------------------------------------------------------------------
-- | Create changes that perform the alignment.
align
:: Maybe Int -- ^ Max columns
-> [Alignable H.SrcSpan] -- ^ Alignables
-> [Change String] -- ^ Changes performing the alignment.
align _ [] = []
align maxColumns alignment
-- Do not make any change if we would go past the maximum number of columns.
| exceedsColumns (longestLeft + longestRight) = []
| not (fixable alignment) = []
| otherwise = map align' alignment
where
exceedsColumns i = case maxColumns of
Nothing -> False -- No number exceeds a maximum column count of
-- Nothing, because there is no limit to exceed.
Just c -> i > c
-- The longest thing in the left column.
longestLeft = maximum $ map (H.srcSpanEndColumn . aLeft) alignment
-- The longest thing in the right column.
longestRight = maximum
[ H.srcSpanEndColumn (aRight a) - H.srcSpanStartColumn (aRight a)
+ aRightLead a
| a <- alignment
]
align' a = changeLine (H.srcSpanStartLine $ aContainer a) $ \str ->
let column = H.srcSpanEndColumn $ aLeft a
(pre, post) = splitAt column str
in [padRight longestLeft (trimRight pre) ++ trimLeft post]
--------------------------------------------------------------------------------
-- | Checks that all the alignables appear on a single line, and that they do
-- not overlap.
fixable :: [Alignable H.SrcSpan] -> Bool
fixable [] = False
fixable [_] = False
fixable fields = all singleLine containers && nonOverlapping containers
where
containers = map aContainer fields
singleLine s = H.srcSpanStartLine s == H.srcSpanEndLine s
nonOverlapping ss = length ss == length (nub $ map H.srcSpanStartLine ss)
|
