LaTeX reader: better support for subfigure package.

A figure with two subfigures turns into two pandoc
figures; the subcaptions are used and the main caption
ignored, unless there are no subcaptions.

Closes #3577.

2 files changed, 46 insertions, 5 deletions

diff --git a/src/Text/Pandoc/Readers/LaTeX.hs b/src/Text/Pandoc/Readers/LaTeX.hs
index f3c94dacb..3e5fae8fb 100644
--- a/src/Text/Pandoc/Readers/LaTeX.hs
+++ b/src/Text/Pandoc/Readers/LaTeX.hs
@@ -39,7 +39,7 @@ import Control.Applicative (many, optional, (<|>))
 import Control.Monad
 import Control.Monad.Except (throwError)
 import Data.Char (chr, isAlphaNum, isLetter, ord)
-import Data.List (intercalate)
+import Data.List (intercalate, isPrefixOf)
 import qualified Data.Map as M
 import Data.Maybe (fromMaybe, maybeToList)
 import Safe (minimumDef)
@@ -1111,10 +1111,11 @@ rawLaTeXInline = do
 
 addImageCaption :: PandocMonad m => Blocks -> LP m Blocks
 addImageCaption = walkM go
-  where go (Image attr alt (src,tit)) = do
+  where go (Image attr alt (src,tit))
+            | not ("fig:" `isPrefixOf` tit) = do
           mbcapt <- stateCaption <$> getState
           return $ case mbcapt of
-               Just ils -> Image attr (toList ils) (src, "fig:")
+               Just ils -> Image attr (toList ils) (src, "fig:" ++ tit)
                Nothing  -> Image attr alt (src,tit)
         go x = return x
 
@@ -1134,8 +1135,8 @@ environments = M.fromList
   , ("letter", env "letter" letterContents)
   , ("minipage", env "minipage" $
          skipopts *> spaces' *> optional braced *> spaces' *> blocks)
-  , ("figure", env "figure" $
-         resetCaption *> skipopts *> blocks >>= addImageCaption)
+  , ("figure", env "figure" $ skipopts *> figure)
+  , ("subfigure", env "subfigure" $ skipopts *> tok *> figure)
   , ("center", env "center" blocks)
   , ("longtable",  env "longtable" $
          resetCaption *> simpTable False >>= addTableCaption)
@@ -1187,6 +1188,11 @@ environments = M.fromList
   , ("alignat*", mathEnv para (Just "aligned") "alignat*")
   ]
 
+figure :: PandocMonad m => LP m Blocks
+figure = try $ do
+  resetCaption
+  blocks >>= addImageCaption
+
 letterContents :: PandocMonad m => LP m Blocks
 letterContents = do
   bs <- blocks
diff --git a/test/command/3577.md b/test/command/3577.md
new file mode 100644
index 000000000..bfeb86eaa
--- /dev/null
+++ b/test/command/3577.md
@@ -0,0 +1,35 @@
+```
+% pandoc -f latex -t html5
+\begin{figure}[ht]
+    \begin{subfigure}{0.45\textwidth}
+        \centering
+        \includegraphics{img1.jpg}
+        \caption{Caption 1}
+    \end{subfigure}
+
+    \begin{subfigure}{0.45\textwidth}
+        \centering
+        \includegraphics{img2.jpg}
+        \caption{Caption 2}
+    \end{subfigure}
+    \caption{Subfigure with Subfloat}
+\end{figure}
+^D
+<figure>
+<img src="img1.jpg" alt="Caption 1" /><figcaption>Caption 1</figcaption>
+</figure>
+<figure>
+<img src="img2.jpg" alt="Caption 2" /><figcaption>Caption 2</figcaption>
+</figure>
+```
+```
+% pandoc -f latex -t html5
+\begin{figure}[ht]
+    \includegraphics{img1.jpg}
+    \caption{Caption 3}
+\end{figure}
+^D
+<figure>
+<img src="img1.jpg" alt="Caption 3" /><figcaption>Caption 3</figcaption>
+</figure>
+```