Raise informative errors when YAML metadata parsing fails.

Closes #6730.

Previously the command would succeed, returning empty metadata,
with no errors or warnings.

API changes:

- Remove now unused CouldNotParseYamlMetadata constructor for
  LogMessage (T.P.Logging).

- Add 'Maybe FilePath' parameter to yamlToMeta in T.P.Readers.Markdown.

6 files changed, 37 insertions, 42 deletions

diff --git a/src/Text/Pandoc/App.hs b/src/Text/Pandoc/App.hs
index 58f605a19..5c3ebaed9 100644
--- a/src/Text/Pandoc/App.hs
+++ b/src/Text/Pandoc/App.hs
@@ -221,8 +221,9 @@ convertWithOpts opts = do
     metadataFromFile <-
       case optMetadataFiles opts of
         []    -> return mempty
-        paths -> mapM readFileLazy paths >>=
-                    fmap mconcat . mapM (yamlToMeta readerOpts)
+        paths -> mconcat <$>
+           mapM (\path -> do raw <- readFileLazy path
+                             yamlToMeta readerOpts (Just path) raw) paths
 
     let transforms = (case optShiftHeadingLevelBy opts of
                           0             -> id
diff --git a/src/Text/Pandoc/Citeproc.hs b/src/Text/Pandoc/Citeproc.hs
index 2a71f619a..202fc5506 100644
--- a/src/Text/Pandoc/Citeproc.hs
+++ b/src/Text/Pandoc/Citeproc.hs
@@ -191,7 +191,7 @@ getRefsFromBib locale idpred t = do
   let fp = T.unpack t
   raw <- readFileStrict fp
   case formatFromExtension fp of
-    Just f -> getRefs locale f idpred raw
+    Just f -> getRefs locale f idpred (Just fp) raw
     Nothing -> throwError $ PandocAppError $
                  "Could not deterine bibliography format for " <> t
 
@@ -199,9 +199,10 @@ getRefs :: PandocMonad m
         => Locale
         -> BibFormat
         -> (Text -> Bool)
+        -> Maybe FilePath
         -> ByteString
         -> m [Reference Inlines]
-getRefs locale format idpred raw =
+getRefs locale format idpred mbfp raw =
   case format of
     Format_bibtex ->
       either (throwError . PandocAppError . T.pack . show) return .
@@ -216,6 +217,7 @@ getRefs locale format idpred raw =
     Format_yaml -> do
       rs <- yamlToRefs idpred
               def{ readerExtensions = pandocExtensions }
+              mbfp
               (L.fromStrict raw)
       return $ mapMaybe metaValueToReference rs
 
diff --git a/src/Text/Pandoc/Logging.hs b/src/Text/Pandoc/Logging.hs
index f6a2a6e1a..5c9330b7b 100644
--- a/src/Text/Pandoc/Logging.hs
+++ b/src/Text/Pandoc/Logging.hs
@@ -61,7 +61,6 @@ instance FromYAML Verbosity where
 data LogMessage =
     SkippedContent Text.Text SourcePos
   | IgnoredElement Text.Text
-  | CouldNotParseYamlMetadata Text.Text SourcePos
   | DuplicateLinkReference Text.Text SourcePos
   | DuplicateNoteReference Text.Text SourcePos
   | NoteDefinedButNotUsed Text.Text SourcePos
@@ -113,11 +112,6 @@ instance ToJSON LogMessage where
             "column" .= sourceColumn pos]
       IgnoredElement s ->
            ["contents" .= s]
-      CouldNotParseYamlMetadata s pos ->
-           ["message" .= s,
-            "source" .= sourceName pos,
-            "line" .= toJSON (sourceLine pos),
-            "column" .= toJSON (sourceColumn pos)]
       DuplicateLinkReference s pos ->
            ["contents" .= s,
             "source" .= sourceName pos,
@@ -251,9 +245,6 @@ showLogMessage msg =
          "Skipped '" <> s <> "' at " <> showPos pos
        IgnoredElement s ->
          "Ignored element " <> s
-       CouldNotParseYamlMetadata s pos ->
-         "Could not parse YAML metadata at " <> showPos pos <>
-           if Text.null s then "" else ": " <> s
        DuplicateLinkReference s pos ->
          "Duplicate link reference '" <> s <> "' at " <> showPos pos
        DuplicateNoteReference s pos ->
@@ -348,7 +339,6 @@ messageVerbosity msg =
   case msg of
        SkippedContent{}              -> INFO
        IgnoredElement{}              -> INFO
-       CouldNotParseYamlMetadata{}   -> WARNING
        DuplicateLinkReference{}      -> WARNING
        DuplicateNoteReference{}      -> WARNING
        NoteDefinedButNotUsed{}       -> WARNING
diff --git a/src/Text/Pandoc/Parsing.hs b/src/Text/Pandoc/Parsing.hs
index b17cace88..8395c96de 100644
--- a/src/Text/Pandoc/Parsing.hs
+++ b/src/Text/Pandoc/Parsing.hs
@@ -179,7 +179,9 @@ module Text.Pandoc.Parsing ( take1WhileP,
                              setSourceColumn,
                              setSourceLine,
                              incSourceColumn,
+                             incSourceLine,
                              newPos,
+                             initialPos,
                              Line,
                              Column
                              )
diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index 1a4c63de0..d8296ea61 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -67,11 +67,17 @@ readMarkdown opts s = do
 -- String scalars in the YAML are parsed as Markdown.
 yamlToMeta :: PandocMonad m
            => ReaderOptions
+           -> Maybe FilePath
            -> BL.ByteString
            -> m Meta
-yamlToMeta opts bstr = do
+yamlToMeta opts mbfp bstr = do
   let parser = do
+        oldPos <- getPosition
+        case mbfp of
+          Nothing -> return ()
+          Just fp -> setPosition $ initialPos fp
         meta <- yamlBsToMeta (fmap B.toMetaValue <$> parseBlocks) bstr
+        setPosition oldPos
         return $ runF meta defaultParserState
   parsed <- readWithM parser def{ stateOptions = opts } ""
   case parsed of
@@ -84,11 +90,17 @@ yamlToMeta opts bstr = do
 yamlToRefs :: PandocMonad m
            => (Text -> Bool)
            -> ReaderOptions
+           -> Maybe FilePath
            -> BL.ByteString
            -> m [MetaValue]
-yamlToRefs idpred opts bstr = do
+yamlToRefs idpred opts mbfp bstr = do
   let parser = do
+        oldPos <- getPosition
+        case mbfp of
+          Nothing -> return ()
+          Just fp -> setPosition $ initialPos fp
         refs <- yamlBsToRefs (fmap B.toMetaValue <$> parseBlocks) idpred bstr
+        setPosition oldPos
         return $ runF refs defaultParserState
   parsed <- readWithM parser def{ stateOptions = opts } ""
   case parsed of
diff --git a/src/Text/Pandoc/Readers/Metadata.hs b/src/Text/Pandoc/Readers/Metadata.hs
index 5154e3174..bdc4c29bf 100644
--- a/src/Text/Pandoc/Readers/Metadata.hs
+++ b/src/Text/Pandoc/Readers/Metadata.hs
@@ -37,21 +37,19 @@ yamlBsToMeta :: PandocMonad m
              -> BL.ByteString
              -> ParserT Text ParserState m (F Meta)
 yamlBsToMeta pMetaValue bstr = do
-  pos <- getPosition
   case YAML.decodeNode' YAML.failsafeSchemaResolver False False bstr of
        Right (YAML.Doc (YAML.Mapping _ _ o):_)
                 -> fmap Meta <$> yamlMap pMetaValue o
        Right [] -> return . return $ mempty
        Right [YAML.Doc (YAML.Scalar _ YAML.SNull)]
                 -> return . return $ mempty
-       Right _  -> do logMessage $ CouldNotParseYamlMetadata "not an object"
-                                   pos
-                      return . return $ mempty
-       Left (_pos, err')
-                -> do logMessage $ CouldNotParseYamlMetadata
-                                   (T.pack err') pos
-                      return . return $ mempty
-
+       Right _  -> fail "expected YAML object"
+       Left (yamlpos, err')
+                -> do pos <- getPosition
+                      setPosition $ incSourceLine
+                            (setSourceColumn pos (YE.posColumn yamlpos))
+                            (YE.posLine yamlpos - 1)
+                      fail err'
 
 fakePos :: YAML.Pos
 fakePos = YAML.Pos (-1) (-1) 1 0
@@ -71,8 +69,7 @@ yamlBsToRefs :: PandocMonad m
              -> (Text -> Bool) -- ^ Filter for id
              -> BL.ByteString
              -> ParserT Text ParserState m (F [MetaValue])
-yamlBsToRefs pMetaValue idpred bstr = do
-  pos <- getPosition
+yamlBsToRefs pMetaValue idpred bstr =
   case YAML.decodeNode' YAML.failsafeSchemaResolver False False bstr of
        Right (YAML.Doc o@(YAML.Mapping _ _ _):_)
                 -> case lookupYAML "references" o of
@@ -90,26 +87,17 @@ yamlBsToRefs pMetaValue idpred bstr = do
                                     Nothing   -> False
                        sequence <$>
                          mapM (yamlToMetaValue pMetaValue) (filter g ns)
-                     Just _ -> do
-                       logMessage $ CouldNotParseYamlMetadata
-                            ("expecting sequence in 'references' field") pos
-                       return . return $ mempty
-                     Nothing -> do
-                       logMessage $ CouldNotParseYamlMetadata
-                                      ("expecting 'references' field") pos
-                       return . return $ mempty
+                     Just _ ->
+                       fail "expecting sequence in 'references' field"
+                     Nothing ->
+                       fail "expecting 'references' field"
 
        Right [] -> return . return $ mempty
        Right [YAML.Doc (YAML.Scalar _ YAML.SNull)]
                 -> return . return $ mempty
-       Right _  -> do logMessage $ CouldNotParseYamlMetadata "not an object"
-                                   pos
-                      return . return $ mempty
+       Right _  -> fail "expecting YAML object"
        Left (_pos, err')
-                -> do logMessage $ CouldNotParseYamlMetadata
-                                   (T.pack err') pos
-                      return . return $ mempty
-
+                -> fail err'
 
 
 nodeToKey :: YAML.Node YE.Pos -> Maybe Text