pptx: Fix logic for choosing Comparison layout

There was a mistake in the logic used to choose between the Comparison
and Two Content layouts: if one column contained only non-text (an image
or a table) and the other contained only text, the Comparison layout was
chosen instead of the desired Two Content layout.

This commit fixes that logic:

> If either column contains text followed by non-text, use Comparison.
  Otherwise, use Two Content.

It also adds a test asserting this behaviour.

pandoc.cabal

@@ -446,8 +446,10 @@ extra-source-files:
                  test/pptx/start-numbering-at/*.pptx
                  test/pptx/tables/input.native
                  test/pptx/tables/*.pptx
-                 test/pptx/two-column/input.native
-                 test/pptx/two-column/*.pptx
+                 test/pptx/two-column/all-text/input.native
+                 test/pptx/two-column/all-text/*.pptx
+                 test/pptx/two-column/text-and-image/input.native
+                 test/pptx/two-column/text-and-image/*.pptx
                  test/ipynb/*.in.native
                  test/ipynb/*.out.native
                  test/ipynb/*.ipynb

src/Text/Pandoc/Writers/Powerpoint/Presentation.hs

@@ -696,10 +696,11 @@ bodyBlocksToSlide _ (blk : blks) spkNotes
               sldId
               (ComparisonSlide [] (shapesL1, shapesL2) (shapesR1, shapesR2))
               spkNotes
-      case (break notText blksL, break notText blksR) of
-        ((_, []), (_, [])) -> mkTwoColumn blksL blksR
-        (([], _), ([], _)) -> mkTwoColumn blksL blksR
-        ((blksL1, blksL2), (blksR1, blksR2)) -> mkComparison blksL1 blksL2 blksR1 blksR2
+      let (blksL1, blksL2) = break notText blksL
+          (blksR1, blksR2) = break notText blksR
+      if (any null [blksL1, blksL2]) && (any null [blksR1, blksR2])
+      then mkTwoColumn blksL blksR
+      else mkComparison blksL1 blksL2 blksR1 blksR2
 bodyBlocksToSlide _ (blk : blks) spkNotes = do
       sldId <- asks envCurSlideId
       inNoteSlide <- asks envInNoteSlide

test/Tests/Writers/Powerpoint.hs

@@ -103,8 +103,12 @@ tests = groupPptxTests [ pptxTests "Inline formatting"
                          "pptx/images/output.pptx"
                        , pptxTests "two-column layout"
                          def
-                         "pptx/two-column/input.native"
-                         "pptx/two-column/output.pptx"
+                         "pptx/two-column/all-text/input.native"
+                         "pptx/two-column/all-text/output.pptx"
+                       , pptxTests "two-column (not comparison)"
+                         def
+                         "pptx/two-column/text-and-image/input.native"
+                         "pptx/two-column/text-and-image/output.pptx"
                        , pptxTests "speaker notes"
                          def
                          "pptx/speaker-notes/input.native"

test/pptx/two-column/text-and-image/input.native

@@ -0,0 +1,12 @@
+[Header 1 ("slide-1",[],[]) [Str "Slide",Space,Str "1"]
+,Div ("",["columns"],[])
+ [Div ("",["column"],[])
+  [Para [Image ("",[],[]) [Str "an",Space,Str "image"] ("lalune.jpg","fig:")]]
+ ,Div ("",["column"],[])
+  [Para [Str "This",Space,Str "should",Space,Str "use",Space,Str "Two",Space,Str "Content,",Space,Emph [Str "not"],Space,Str "Comparison!"]]]
+,Header 1 ("slide-2",[],[]) [Str "Slide",Space,Str "2"]
+,Div ("",["columns"],[])
+ [Div ("",["column"],[])
+  [Para [Str "This",Space,Str "should",Space,Str "also",Space,Str "use",Space,Str "Two",Space,Str "Content"]]
+ ,Div ("",["column"],[])
+  [Para [Image ("",[],[]) [Str "an",Space,Str "image"] ("lalune.jpg","fig:")]]]]