From 38daf9de6881251c8f0300da1701172c773d4f49 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Fri, 17 Feb 2017 12:56:07 +0100
Subject: [PATCH] Parsing:  Added HasLogMessages, logMessage,
 reportLogMessages.

We need to do logging by updating parser state, or we'll get
inappropriate and repeated log messages when there is parser
backtracking.

See #3447.
---
 src/Text/Pandoc/Parsing.hs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/Text/Pandoc/Parsing.hs b/src/Text/Pandoc/Parsing.hs
index 933d0161e..e0d9c5528 100644
--- a/src/Text/Pandoc/Parsing.hs
+++ b/src/Text/Pandoc/Parsing.hs
@@ -73,11 +73,14 @@ module Text.Pandoc.Parsing ( anyLine,
                              guardDisabled,
                              updateLastStrPos,
                              notAfterString,
+                             logMessage,
+                             reportLogMessages,
                              ParserState (..),
                              HasReaderOptions (..),
                              HasHeaderMap (..),
                              HasIdentifierList (..),
                              HasMacros (..),
+                             HasLogMessages (..),
                              HasLastStrPosition (..),
                              defaultParserState,
                              HeaderType (..),
@@ -934,6 +937,7 @@ data ParserState = ParserState
       stateCaption         :: Maybe Inlines, -- ^ Caption in current environment
       stateInHtmlBlock     :: Maybe String,  -- ^ Tag type of HTML block being parsed
       stateContainers      :: [String],      -- ^ parent include files
+      stateLogMessages     :: [LogMessage],  -- ^ log messages
       stateMarkdownAttribute :: Bool         -- ^ True if in markdown=1 context
     }
 
@@ -1003,6 +1007,14 @@ instance HasLastStrPosition ParserState where
   setLastStrPos pos st = st{ stateLastStrPos = Just pos }
   getLastStrPos st     = stateLastStrPos st
 
+class HasLogMessages st where
+  addLogMessage :: LogMessage -> st -> st
+  getLogMessages :: st -> [LogMessage]
+
+instance HasLogMessages ParserState where
+  addLogMessage msg st = st{ stateLogMessages = msg : stateLogMessages st }
+  getLogMessages st = reverse $ stateLogMessages st
+
 defaultParserState :: ParserState
 defaultParserState =
     ParserState { stateOptions         = def,
@@ -1030,9 +1042,22 @@ defaultParserState =
                   stateCaption         = Nothing,
                   stateInHtmlBlock     = Nothing,
                   stateContainers      = [],
+                  stateLogMessages     = [],
                   stateMarkdownAttribute = False
                   }
 
+-- | Add a log message.
+logMessage :: (Stream s m a, HasLogMessages st)
+           => LogMessage -> ParserT s st m ()
+logMessage msg = updateState (addLogMessage msg)
+
+-- | Report all the accumulated log messages, according to verbosity level.
+reportLogMessages :: (PandocMonad m, Stream s m a, HasLogMessages st)
+                  => ParserT s st m ()
+reportLogMessages = do
+  msgs <- getLogMessages <$> getState
+  mapM_ report msgs
+
 -- | Succeed only if the extension is enabled.
 guardEnabled :: (Stream s m a,  HasReaderOptions st) => Extension -> ParserT s st m ()
 guardEnabled ext = getOption readerExtensions >>= guard . extensionEnabled ext