Improper empty cell filtering in LaTeX reader

[despresc]

In Readers.LaTeX the following is done to work around the fact that LaTeX tables explicitly note the grid spaces taken up by multirowand multicolumn cells:

pandoc/src/Text/Pandoc/Readers/LaTeX.hs

Lines 2171 to 2173 in 22babd5

	-- Because of table normalization performed by Text.Pandoc.Builder.table,
	-- we need to remove empty cells
	return $ Row nullAttr $ filter (\c -> c /= emptyCell) cells

It fixes the problem, but it also removes empty cells that don't denote such grid spaces.

E.g. using master on this LaTeX input:

\documentclass{article}

\begin{document}
\begin{tabular}{|r|r|r|}
  A &   & B \\
    & C &
\end{tabular}
\end{document}

gives this native output:

[Table ("",[],[]) (Caption Nothing
 [])
 [(AlignRight,ColWidthDefault)
 ,(AlignRight,ColWidthDefault)
 ,(AlignRight,ColWidthDefault)]
 (TableHead ("",[],[])
 [])
 [(TableBody ("",[],[]) (RowHeadColumns 0)
  []
  [Row ("",[],[])
   [Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "A"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "B"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    []]
  ,Row ("",[],[])
   [Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "C"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    []
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    []]])]
 (TableFoot ("",[],[])
 [])]

and you can see that the space between A and B is gone, and C has migrated to the first column.

[despresc]

This can't be fixed in parseTableRow locally. Either the relevant data about \multirow cells need to be passed in to parseTableRow so that the two types of emptyCell can be distinguished, or the parsed table needs to be fixed up at the very end, in simpTable. The latter is probably cleaner.

[jgm]

Bringing @LaurentRDC into the discussion.
I guess I was right to wonder about the empty cell filtering in that PR (#6608)!

[LaurentRDC]

@jgm Oups, you were right. I'm sorry this is causing trouble.

I have a very busy month of September, so I won't have time to formulate a solution soon unfortunately

[jgm]

If someone else can put together a PR sooner, it would be good to get this fixed.

[despresc]

I should be able to do that.