Markdown reader: use title of implicit figure as short caption.

The title of an implicit figure, if set, is used as the short caption of
a figure. The short caption of a figure replaces the full caption in the
list of figures.

Closes: jgm#7915

src/Text/Pandoc/Readers/Markdown.hs

@@ -1092,7 +1092,9 @@ implicitFigure (ident, classes, attribs) capt url title =
  _ -> capt
  attribs' = filter ((/= "alt") . fst) attribs
  figattr = (ident, mempty, mempty)
- caption = B.simpleCaption $ B.plain capt
+ caption = if T.null title
+ then B.simpleCaption $ B.plain capt
+ else B.caption (Just . B.toList $ B.text title) $ B.plain capt
  figbody = B.plain $ B.imageWith ("", classes, attribs') url title alt
  in B.figureWith figattr caption figbody
 

src/Text/Pandoc/Writers/Markdown.hs

@@ -672,21 +672,22 @@ blockToMarkdown' opts (Figure figattr capt body) = do
  let combinedAttr imgattr = case imgattr of
  ("", cls, kv) | (figid, [], []) <- figattr -> Just (figid, cls, kv)
  _ -> Nothing
- let combinedAlt alt = case capt of
+ let combinedAlt alt title = case capt of
  Caption Nothing [] -> if null alt
  then Just [Str "image"]
  else Just alt
- Caption Nothing [Plain captInlines]
- | captInlines == alt -> Just captInlines
+ Caption short [Plain captInlines]
+ | captInlines == alt
+ , title == maybe "" stringify short -> Just captInlines
  _ -> Nothing
  case body of
  [Plain [Image imgAttr alt (src, ttl)]]
  | isEnabled Ext_implicit_figures opts
- , Just descr <- combinedAlt alt
+ , Just descr <- combinedAlt alt ttl
  , Just imgAttr' <- combinedAttr imgAttr
  , isEnabled Ext_link_attributes opts || imgAttr' == nullAttr
  -> do
- -- use implicit figures if possible
+ -- Lossless representation as implicit figure is possible
  let tgt' = (src, fromMaybe ttl $ T.stripPrefix "fig:" ttl)
  contents <- inlineListToMarkdown opts [Image imgAttr' descr tgt']
  return $ contents <> blankline

test/testsuite.native

@@ -1908,7 +1908,17 @@ Pandoc
  ]
  , Figure
  ( "" , [] , [] )
- (Caption Nothing [ Plain [ Str "lalune" ] ])
+ (Caption
+ (Just
+ [ Str "Voyage"
+ , Space
+ , Str "dans"
+ , Space
+ , Str "la"
+ , Space
+ , Str "Lune"
+ ])
+ [ Plain [ Str "lalune" ] ])
  [ Plain
  [ Image
  ( "" , [] , [] )

test/writer.context

@@ -931,7 +931,7 @@ or here: <http://example.com/>
 
 From \quotation{Voyage dans la Lune} by Georges Melies (1902):
 
-\startplacefigure[title={lalune}]
+\startplacefigure[title={lalune},list={Voyage dans la Lune}]
 {\externalfigure[lalune.jpg]}
 \stopplacefigure
 

test/writer.latex

@@ -951,7 +951,7 @@ From ``Voyage dans la Lune'' by Georges Melies (1902):
 \begin{figure}
 \centering
 \includegraphics{lalune.jpg}
-\caption{lalune}
+\caption[Voyage dans la Lune]{lalune}
 \end{figure}
 
 Here is a movie \includegraphics{movie.jpg} icon.

test/writer.native

@@ -1843,7 +1843,17 @@ Pandoc
  ]
  , Figure
  ( "" , [] , [] )
- (Caption Nothing [ Plain [ Str "lalune" ] ])
+ (Caption
+ (Just
+ [ Str "Voyage"
+ , Space
+ , Str "dans"
+ , Space
+ , Str "la"
+ , Space
+ , Str "Lune"
+ ])
+ [ Plain [ Str "lalune" ] ])
  [ Plain
  [ Image
  ( "" , [] , [] )