imp: journal: support decimal-mark directive in journal files

To match csv-rule and override amount-style as described in
https://github.com/simonmichael/hledger/issues/1670

hledger-lib/Hledger/Read/JournalReader.hs

@@ -246,6 +246,7 @@ directivep = (do
    ,defaultcommoditydirectivep
    ,commodityconversiondirectivep
    ,ignoredpricecommoditydirectivep
+   ,decimalmarkdirectivep
    ]
   ) <?> "directive"
 
@@ -317,6 +318,7 @@ includedirectivep = do
       jparsedefaultyear      = jparsedefaultyear j
       ,jparsedefaultcommodity = jparsedefaultcommodity j
       ,jparseparentaccounts   = jparseparentaccounts j
+      ,jparsedecimalmark      = jparsedecimalmark j
       ,jparsealiases          = jparsealiases j
       ,jcommodities           = jcommodities j
       -- ,jparsetransactioncount = jparsetransactioncount j
@@ -599,6 +601,18 @@ commodityconversiondirectivep = do
   lift restofline
   return ()
 
+-- | Read a valid decimal mark from the decimal-mark directive e.g
+--
+-- decimal-mark ,
+decimalmarkdirectivep :: JournalParser m ()
+decimalmarkdirectivep = do
+  string "decimal-mark" <?> "decimal mark"
+  lift skipNonNewlineSpaces1
+  mark <- satisfy isDecimalMark
+  modify' $ \j -> j{jparsedecimalmark=Just mark}
+  lift restofline
+  return ()
+
 --- *** transactions
 
 -- | Parse a transaction modifier (auto postings) rule.

hledger/test/journal/commas.journal

@@ -0,0 +1,4 @@
+decimal-mark ,
+2021-05-01 YANDEX.PLUS
+    Assets:Yandex            -199,00 RUB
+    Expenses:Unknown:RUB

hledger/test/journal/directive-decimal-mark.test

@@ -0,0 +1,22 @@
+# 1. Commas specified as decimal mark
+$ hledger -f commas.journal bal
+         -199,00 RUB  Assets:Yandex
+          199,00 RUB  Expenses:Unknown:RUB
+--------------------
+                   0  
+>=0
+
+# 2. Include file with different decimal mark
+<
+commodity 1000.00 RUB
+include commas.journal
+2021-05-19 MTS Phone
+    Assets:Yandex         -100.5 RUB
+    Expenses:Phone         100.5 RUB
+$ hledger -f - bal
+         -299.50 RUB  Assets:Yandex
+          100.50 RUB  Expenses:Phone
+          199.00 RUB  Expenses:Unknown:RUB
+--------------------
+                   0  
+>=0