RST writer: use simple tables when possible.

Closes #4750.

Text.Pandoc.Writers.Shared now exports hasSimpleCells [API change].

4 files changed, 82 insertions, 42 deletions

diff --git a/src/Text/Pandoc/Writers/RST.hs b/src/Text/Pandoc/Writers/RST.hs
index 34d5cce04..d64529c21 100644
--- a/src/Text/Pandoc/Writers/RST.hs
+++ b/src/Text/Pandoc/Writers/RST.hs
@@ -35,7 +35,7 @@ module Text.Pandoc.Writers.RST ( writeRST, flatten ) where
 import Prelude
 import Control.Monad.State.Strict
 import Data.Char (isSpace, toLower)
-import Data.List (isPrefixOf, stripPrefix)
+import Data.List (isPrefixOf, stripPrefix, transpose)
 import Data.Maybe (fromMaybe)
 import Data.Text (Text, stripEnd)
 import qualified Text.Pandoc.Builder as B
@@ -304,9 +304,12 @@ blockToRST (Table caption aligns widths headers rows) = do
          modify $ \st -> st{ stOptions = oldOpts }
          return result
   opts <- gets stOptions
-  tbl <- gridTable opts blocksToDoc (all null headers)
-            (map (const AlignDefault) aligns) widths
-            headers rows
+  let isSimple = all (== 0) widths
+  tbl <- if isSimple
+            then simpleTable opts blocksToDoc headers rows
+            else gridTable opts blocksToDoc (all null headers)
+                  (map (const AlignDefault) aligns) widths
+                  headers rows
   return $ if null caption
               then tbl $$ blankline
               else (".. table:: " <> caption') $$ blankline $$ nest 3 tbl $$
@@ -693,3 +696,30 @@ imageDimsToRST attr = do
                           Just dim -> cols dim
                           Nothing  -> empty
   return $ cr <> name $$ showDim Width $$ showDim Height
+
+simpleTable :: PandocMonad m
+            => WriterOptions
+            -> (WriterOptions -> [Block] -> m Doc)
+            -> [[Block]]
+            -> [[[Block]]]
+            -> m Doc
+simpleTable opts blocksToDoc headers rows = do
+  -- can't have empty cells in first column:
+  let fixEmpties (d:ds) = if isEmpty d
+                             then text "\\ " : ds
+                             else d : ds
+      fixEmpties [] = []
+  headerDocs <- if all null headers
+                   then return []
+                   else fixEmpties <$> mapM (blocksToDoc opts) headers
+  rowDocs <- mapM (fmap fixEmpties . mapM (blocksToDoc opts)) rows
+  let numChars [] = 0
+      numChars xs = maximum . map offset $ xs
+  let colWidths = map numChars $ transpose (headerDocs : rowDocs)
+  let toRow = hsep . zipWith lblock colWidths
+  let hline = hsep (map (\n -> text (replicate n '=')) colWidths)
+  let hdr = if all null headers
+               then mempty
+               else hline $$ toRow headerDocs
+  let bdy = vcat $ map toRow rowDocs
+  return $ hdr $$ hline $$ bdy $$ hline
diff --git a/src/Text/Pandoc/Writers/Shared.hs b/src/Text/Pandoc/Writers/Shared.hs
index a7bf30aaa..ed2c46d7b 100644
--- a/src/Text/Pandoc/Writers/Shared.hs
+++ b/src/Text/Pandoc/Writers/Shared.hs
@@ -41,6 +41,7 @@ module Text.Pandoc.Writers.Shared (
                      , isDisplayMath
                      , fixDisplayMath
                      , unsmartify
+                     , hasSimpleCells
                      , gridTable
                      , lookupMetaBool
                      , lookupMetaBlocks
@@ -54,6 +55,7 @@ module Text.Pandoc.Writers.Shared (
 where
 import Prelude
 import Control.Monad (zipWithM)
+import Data.Monoid (Any (..))
 import Data.Aeson (FromJSON (..), Result (..), ToJSON (..), Value (Object),
                    encode, fromJSON)
 import Data.Char (chr, ord, isAscii, isSpace)
@@ -70,6 +72,7 @@ import Text.Pandoc.Pretty
 import Text.Pandoc.Shared (stringify)
 import Text.Pandoc.UTF8 (toStringLazy)
 import Text.Pandoc.XML (escapeStringForXML)
+import Text.Pandoc.Walk (query)
 import Text.Printf (printf)
 
 -- | Create JSON value for template from a 'Meta' and an association list
@@ -243,6 +246,21 @@ unsmartify opts ('\8216':xs) = '\'' : unsmartify opts xs
 unsmartify opts (x:xs) = x : unsmartify opts xs
 unsmartify _ [] = []
 
+-- | True if block is a table that can be represented with
+-- one line per row.
+hasSimpleCells :: Block -> Bool
+hasSimpleCells (Table _caption _aligns _widths headers rows) =
+  all isSimpleCell (concat (headers:rows))
+  where
+    isLineBreak LineBreak = Any True
+    isLineBreak _         = Any False
+    hasLineBreak = getAny . query isLineBreak
+    isSimpleCell [Plain ils] = not (hasLineBreak ils)
+    isSimpleCell [Para ils ] = not (hasLineBreak ils)
+    isSimpleCell []          = True
+    isSimpleCell _           = False
+hasSimpleCells _ = False
+
 gridTable :: Monad m
           => WriterOptions
           -> (WriterOptions -> [Block] -> m Doc)
diff --git a/test/tables-rstsubset.native b/test/tables-rstsubset.native
index 5ea520d7c..a4f801b1c 100644
--- a/test/tables-rstsubset.native
+++ b/test/tables-rstsubset.native
@@ -1,5 +1,5 @@
 [Para [Str "Simple",Space,Str "table",Space,Str "with",Space,Str "caption:"]
-,Table [Str "Demonstration",Space,Str "of",Space,Str "simple",Space,Str "table",Space,Str "syntax."] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [0.1,8.75e-2,0.1125,0.125]
+,Table [Str "Demonstration",Space,Str "of",Space,Str "simple",Space,Str "table",Space,Str "syntax."] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [0.0,0.0,0.0,0.0]
  [[Plain [Str "Right"]]
  ,[Plain [Str "Left"]]
  ,[Plain [Str "Center"]]
@@ -17,7 +17,7 @@
   ,[Plain [Str "1"]]
   ,[Plain [Str "1"]]]]
 ,Para [Str "Simple",Space,Str "table",Space,Str "without",Space,Str "caption:"]
-,Table [] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [0.1,8.75e-2,0.1125,0.125]
+,Table [] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [0.0,0.0,0.0,0.0]
  [[Plain [Str "Right"]]
  ,[Plain [Str "Left"]]
  ,[Plain [Str "Center"]]
@@ -35,7 +35,7 @@
   ,[Plain [Str "1"]]
   ,[Plain [Str "1"]]]]
 ,Para [Str "Simple",Space,Str "table",Space,Str "indented",Space,Str "two",Space,Str "spaces:"]
-,Table [Str "Demonstration",Space,Str "of",Space,Str "simple",Space,Str "table",Space,Str "syntax."] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [0.1,8.75e-2,0.1125,0.125]
+,Table [Str "Demonstration",Space,Str "of",Space,Str "simple",Space,Str "table",Space,Str "syntax."] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [0.0,0.0,0.0,0.0]
  [[Plain [Str "Right"]]
  ,[Plain [Str "Left"]]
  ,[Plain [Str "Center"]]
@@ -81,7 +81,7 @@
   ,[Plain [Str "5.0"]]
   ,[Plain [Str "Here\8217s",Space,Str "another",Space,Str "one.",Space,Str "Note",SoftBreak,Str "the",Space,Str "blank",Space,Str "line",Space,Str "between",SoftBreak,Str "rows."]]]]
 ,Para [Str "Table",Space,Str "without",Space,Str "column",Space,Str "headers:"]
-,Table [] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [7.5e-2,7.5e-2,7.5e-2,7.5e-2]
+,Table [] [AlignDefault,AlignDefault,AlignDefault,AlignDefault] [0.0,0.0,0.0,0.0]
  [[]
  ,[]
  ,[]
diff --git a/test/tables.rst b/test/tables.rst
index 4559883cd..660df61d4 100644
--- a/test/tables.rst
+++ b/test/tables.rst
@@ -2,41 +2,35 @@ Simple table with caption:
 
 .. table:: Demonstration of simple table syntax.
 
-   +-------+------+--------+---------+
-   | Right | Left | Center | Default |
-   +=======+======+========+=========+
-   | 12    | 12   | 12     | 12      |
-   +-------+------+--------+---------+
-   | 123   | 123  | 123    | 123     |
-   +-------+------+--------+---------+
-   | 1     | 1    | 1      | 1       |
-   +-------+------+--------+---------+
+   ===== ==== ====== =======
+   Right Left Center Default
+   ===== ==== ====== =======
+   12    12   12     12
+   123   123  123    123
+   1     1    1      1
+   ===== ==== ====== =======
 
 Simple table without caption:
 
-+-------+------+--------+---------+
-| Right | Left | Center | Default |
-+=======+======+========+=========+
-| 12    | 12   | 12     | 12      |
-+-------+------+--------+---------+
-| 123   | 123  | 123    | 123     |
-+-------+------+--------+---------+
-| 1     | 1    | 1      | 1       |
-+-------+------+--------+---------+
+===== ==== ====== =======
+Right Left Center Default
+===== ==== ====== =======
+12    12   12     12
+123   123  123    123
+1     1    1      1
+===== ==== ====== =======
 
 Simple table indented two spaces:
 
 .. table:: Demonstration of simple table syntax.
 
-   +-------+------+--------+---------+
-   | Right | Left | Center | Default |
-   +=======+======+========+=========+
-   | 12    | 12   | 12     | 12      |
-   +-------+------+--------+---------+
-   | 123   | 123  | 123    | 123     |
-   +-------+------+--------+---------+
-   | 1     | 1    | 1      | 1       |
-   +-------+------+--------+---------+
+   ===== ==== ====== =======
+   Right Left Center Default
+   ===== ==== ====== =======
+   12    12   12     12
+   123   123  123    123
+   1     1    1      1
+   ===== ==== ====== =======
 
 Multiline table with caption:
 
@@ -70,13 +64,11 @@ Multiline table without caption:
 
 Table without column headers:
 
-+-----+-----+-----+-----+
-| 12  | 12  | 12  | 12  |
-+-----+-----+-----+-----+
-| 123 | 123 | 123 | 123 |
-+-----+-----+-----+-----+
-| 1   | 1   | 1   | 1   |
-+-----+-----+-----+-----+
+=== === === ===
+12  12  12  12
+123 123 123 123
+1   1   1   1
+=== === === ===
 
 Multiline table without column headers: