RST reader: parse :alt: on figure.

Also give a better default if `alt` is not specified, using
the stringified caption rather than the filename.

Partially addresses #11140.

Add failing test case for Markdown writer issue in #11140.

src/Text/Pandoc/Readers/RST.hs

@@ -855,8 +855,9 @@ directive' = do
            let figcls = concatMap (T.words . snd) figclasskv
            let figattr = ("", figcls ++ aligncls, [])
            let capt = B.caption Nothing (B.plain caption <> legend)
+           let alt = maybe caption (B.text . trim) (lookup "alt" fields)
            return $ B.figureWith figattr capt $
-             B.plain (B.imageWith (imgident, imgcls, imgkvs) src "" (B.text src))
+             B.plain (B.imageWith (imgident, imgcls, imgkvs) src "" alt)
         "image" -> do
            let src = escapeURI $ trim top
            let alt = B.str $ maybe "image" trim $ lookup "alt" fields

test/command/11140.md

@@ -0,0 +1,52 @@
+```
+% pandoc -f rst -t native
+.. figure:: image.png
+   :alt: my alt
+
+   Caption
+^D
+[ Figure
+    ( "" , [] , [] )
+    (Caption Nothing [ Plain [ Str "Caption" ] ])
+    [ Plain
+        [ Image
+            ( "" , [] , [] )
+            [ Str "my" , Space , Str "alt" ]
+            ( "image.png" , "" )
+        ]
+    ]
+]
+```
+
+```
+% pandoc -f rst -t native
+.. figure:: image.png
+
+   Caption
+^D
+[ Figure
+    ( "" , [] , [] )
+    (Caption Nothing [ Plain [ Str "Caption" ] ])
+    [ Plain
+        [ Image
+            ( "" , [] , [] ) [ Str "Caption" ] ( "image.png" , "" )
+        ]
+    ]
+]
+```
+
+```
+% pandoc -f native -t markdown
+[ Figure
+    ( "" , [] , [] )
+    (Caption
+       Nothing [ Plain [ Str "Caption" ] ])
+    [ Plain
+        [ Image ( "" , [] , [] ) [ Str "my", Space, Str "alt" ] ( "image.png" , "" )
+        ]
+    ]
+]
+^D
+![Caption](image.png){alt="my alt"}
+```
+

test/command/5619.md

@@ -37,7 +37,28 @@
     [ Plain
         [ Image
             ( "test" , [] , [ ( "width" , "1in" ) ] )
-            [ Str "img1.jpg" ]
+            [ Str "The"
+            , Space
+            , Str "caption."
+            , Space
+            , Str "Here's"
+            , Space
+            , Str "what"
+            , Space
+            , Str "piggybacking"
+            , Space
+            , Str "on"
+            , Space
+            , Str "caption"
+            , Space
+            , Str "would"
+            , Space
+            , Str "look"
+            , Space
+            , Str "like"
+            , Space
+            , Str "{#fig:1}"
+            ]
             ( "img1.jpg" , "" )
         ]
     ]

test/command/7473.md

@@ -24,7 +24,14 @@
     [ Plain
         [ Image
             ( "" , [] , [ ( "width" , "1in" ) ] )
-            [ Str "example.png" ]
+            [ Str "This"
+            , Space
+            , Str "is"
+            , Space
+            , Str "a"
+            , Space
+            , Str "caption."
+            ]
             ( "example.png" , "" )
         ]
     ]

test/command/rst_block_subst.md

@@ -11,9 +11,7 @@
     (Caption Nothing [ Plain [ Str "capt" ] ])
     [ Plain
         [ Image
-            ( "" , [] , [] )
-            [ Str "img/dummy.png" ]
-            ( "img/dummy.png" , "" )
+            ( "" , [] , [] ) [ Str "capt" ] ( "img/dummy.png" , "" )
         ]
     ]
 ]