Change merge behavior for metadata.

Previously, if a document contained two YAML metadata blocks
that set the same field, the conflict would be resolved in favor
of the first. Now it is resolved in favor of the second (due to
a change in pandoc-types).

This makes the behavior more uniform with other things in pandoc
(such as reference links and `--metadata-file`).

MANUAL.txt

@@ -3883,9 +3883,9 @@ given a role by external processors.)  Field names must not be
 interpretable as YAML numbers or boolean values (so, for
 example, `yes`, `True`, and `15` cannot be used as field names).
 
-A document may contain multiple metadata blocks.  The metadata fields will
-be combined through a *left-biased union*:  if two metadata blocks attempt
-to set the same field, the value from the first block will be taken.
+A document may contain multiple metadata blocks.  If two
+metadata blocks attempt to set the same field, the value from
+the second block will be taken.
 
 When pandoc is used with `-t markdown` to create a Markdown document,
 a YAML metadata block will be produced only if the `-s/--standalone`

cabal.project

@@ -13,3 +13,7 @@ source-repository-package
     location: https://github.com/jgm/pandoc-citeproc
     tag: 0.16.3.1
 
+source-repository-package
+    type: git
+    location: git: https://github.com/jgm/pandoc-types
+    tag: 00f7bb79e79d7cfd3523880dbc64ba3ea46c3da2

src/Text/Pandoc/App.hs

@@ -230,12 +230,8 @@ convertWithOpts opts = do
     metadataFromFile <-
       case optMetadataFiles opts of
         []    -> return mempty
-        paths -> mapM readFileLazy paths >>= mapM (yamlToMeta readerOpts)
-                   >>= return . (foldr1 (<>))
-        -- Note: this list is in reverse order from the order on the
-        -- command line.  So this code ensures that metadata files
-        -- specified later in the command line take precedence over
-        -- those specified earlier.
+        paths -> mapM readFileLazy paths >>=
+                    fmap mconcat . mapM (yamlToMeta readerOpts)
 
     let transforms = (case optShiftHeadingLevelBy opts of
                           0             -> id
@@ -286,8 +282,8 @@ convertWithOpts opts = do
               (   (if isJust (optExtractMedia opts)
                       then fillMediaBag
                       else return)
-              >=> return . adjustMetadata (<> metadataFromFile)
-              >=> return . adjustMetadata (metadata <>)
+              >=> return . adjustMetadata (metadataFromFile <>)
+              >=> return . adjustMetadata (<> metadata)
               >=> applyTransforms transforms
               >=> applyFilters readerOpts filters' [format]
               >=> maybe return extractMedia (optExtractMedia opts)

src/Text/Pandoc/App/CommandLineOptions.hs

@@ -155,7 +155,7 @@ options =
     , Option "" ["metadata-file"]
                  (ReqArg
                   (\arg opt -> return opt{ optMetadataFiles =
-                    normalizePath arg : optMetadataFiles opt })
+                      optMetadataFiles opt ++ [normalizePath arg] })
                   "FILE")
                  ""
 

src/Text/Pandoc/Readers/Vimwiki.hs

@@ -427,7 +427,9 @@ ph s = try $ do
   contents <- trimInlines . mconcat <$> manyTill inline (lookAhead newline)
     --use lookAhead because of placeholder in the whitespace parser
   let meta' = B.setMeta s contents nullMeta
-  updateState $ \st -> st { stateMeta = stateMeta st <> meta' }
+  -- this order ensures that later values will be ignored in favor
+  -- of earlier ones:
+  updateState $ \st -> st { stateMeta = meta' <> stateMeta st }
 
 noHtmlPh :: PandocMonad m => VwParser m ()
 noHtmlPh = try $

stack.yaml

@@ -13,7 +13,7 @@ packages:
 - '.'
 extra-deps:
 - pandoc-citeproc-0.16.3.1
-- pandoc-types-1.17.6.1
+#- pandoc-types-1.17.6.1
 - texmath-0.11.3
 - haddock-library-1.8.0
 - skylighting-0.8.2.3
@@ -23,6 +23,8 @@ extra-deps:
 - HsYAML-0.2.0.0
 - HsYAML-aeson-0.2.0.0
 - doctemplates-0.7
+- git: https://github.com/jgm/pandoc-types
+  commit: 00f7bb79e79d7cfd3523880dbc64ba3ea46c3da2
 ghc-options:
    "$locals": -fhide-source-paths -Wno-missing-home-modules
 resolver: lts-14.6

test/command/multiple-metadata-blocks.md

@@ -10,6 +10,6 @@ foo: bar
 foo: bim
 ...
 ^D
-Pandoc (Meta {unMeta = fromList [("foo",MetaInlines [Str "bar"])]})
+Pandoc (Meta {unMeta = fromList [("foo",MetaInlines [Str "bim"])]})
 []
 ```