Revealjs writer: default scrollProgress to 'auto'.

RevealJS defaults scrollProgress to 'auto', but the writer was
setting it to true.  Use lookupMeta to distinguish between
MetaBool True, MetaBool False, and unset (defaulting to 'auto').
The template uses a helper variable scrollProgressAuto since
pandoc templates cannot distinguish a MetaString "auto" from
MetaBool True in a single variable.

data/templates/default.revealjs

@@ -243,7 +243,13 @@ $if(view)$
         // Enable scroll view
         view: '$view/nowrap$',
         // see https://revealjs.com/scroll-view/#scrollbar
+$if(scrollProgressAuto)$
+        scrollProgress: 'auto',
+$elseif(scrollProgress)$
         scrollProgress: $scrollProgress$,
+$else$
+        scrollProgress: false,
+$endif$
         // see https://revealjs.com/scroll-view/#url-activation
         scrollActivationWidth: $scrollActivationWidth$,
         // see https://revealjs.com/scroll-view/#scroll-snapping

src/Text/Pandoc/Writers/HTML.hs

@@ -434,7 +434,11 @@ pandocToHtml opts (Pandoc meta blocks) = do
                          defField "backgroundTransition" ("fade" :: Doc Text) .
                          defField "viewDistance" ("3" :: Doc Text) .
                          defField "mobileViewDistance" ("2" :: Doc Text) .
-                         defField "scrollProgress" True .
+                         (case lookupMeta "scrollProgress" meta of
+                            Just (MetaBool False) -> id
+                            Just (MetaBool True)  ->
+                              defField "scrollProgress" True
+                            _  -> defField "scrollProgressAuto" True) .
                          defField "scrollActivationWidth" ("0" :: Doc Text) .
                          defField "scrollSnap" ("mandatory" :: Doc Text) .
                          defField "scrollLayout" ("full" :: Doc Text) .

test/command/11486.md

@@ -6,6 +6,7 @@ view: scroll
 ^D
         scrollActivationWidth: 0,
         scrollSnap: 'mandatory',
+        scrollProgress: 'auto',
 ```
 
 ```
@@ -17,6 +18,7 @@ scrollSnap: false
 ^D
         scrollActivationWidth: 0,
         scrollSnap: false,
+        scrollProgress: 'auto',
 ```
 
 ```
@@ -28,6 +30,7 @@ scrollSnap: proximity
 ^D
         scrollActivationWidth: 0,
         scrollSnap: 'proximity',
+        scrollProgress: 'auto',
 ```
 
 ```
@@ -39,4 +42,41 @@ scrollActivationWidth: 500
 ^D
         scrollActivationWidth: 500,
         scrollSnap: 'mandatory',
+        scrollProgress: 'auto',
+```
+
+```
+% pandoc -t revealjs --template=command/11486/scroll.revealjs
+---
+view: scroll
+scrollProgress: true
+---
+^D
+        scrollActivationWidth: 0,
+        scrollSnap: 'mandatory',
+        scrollProgress: true,
+```
+
+```
+% pandoc -t revealjs --template=command/11486/scroll.revealjs
+---
+view: scroll
+scrollProgress: false
+---
+^D
+        scrollActivationWidth: 0,
+        scrollSnap: 'mandatory',
+        scrollProgress: false,
+```
+
+```
+% pandoc -t revealjs --template=command/11486/scroll.revealjs
+---
+view: scroll
+scrollProgress: auto
+---
+^D
+        scrollActivationWidth: 0,
+        scrollSnap: 'mandatory',
+        scrollProgress: 'auto',
 ```

test/command/11486/scroll.revealjs

@@ -5,4 +5,11 @@ $if(scrollSnap)$
 $else$
         scrollSnap: false,
 $endif$
+$if(scrollProgressAuto)$
+        scrollProgress: 'auto',
+$elseif(scrollProgress)$
+        scrollProgress: $scrollProgress$,
+$else$
+        scrollProgress: false,
+$endif$
 $endif$