identify the commodity in balance assertion errors

Now that balance assertions are checking only a single commodity, it can
be confusing. Eg say all your amounts are in dollars, an assertion like
"= 0" checked the dollar balance in hledger 0.23 but always succeeds in
hledger 0.24. When an assertion fails, we now report which commodity was
checked to help troubleshooting.

hledger-lib/Hledger/Data/Journal.hs

@@ -440,16 +440,16 @@ checkBalanceAssertion (errs,startbal) ps
     p = last ps
     assertion = pbalanceassertion p
     Just assertedbal = dbg2 "assertedbal" assertion
+    assertedcomm = dbg2 "assertedcomm" $ maybe "" acommodity $ headMay $ amounts assertedbal
     fullbal = dbg2 "fullbal" $ sum $ [dbg2 "startbal" startbal] ++ map pamount ps
-    singlebal = dbg2 "singlebal" $
-                let c = maybe "" acommodity $ headMay $ amounts assertedbal
-                in filterMixedAmount (\a -> acommodity a == c) fullbal
+    singlebal = dbg2 "singlebal" $ filterMixedAmount (\a -> acommodity a == assertedcomm) fullbal
     bal = singlebal -- check single-commodity balance like Ledger; maybe add == FULLBAL later
-    err = printf "Balance assertion failed for account %s on %s\n%sAfter posting:\n   %s\nexpected commodity balance is %s, calculated balance was %s."
+    err = printf "Balance assertion failed for account %s on %s\n%sAfter posting:\n   %s\nexpected balance in commodity \"%s\" is %s, calculated balance was %s."
                  (paccount p)
                  (show $ postingDate p)
                  (maybe "" (("In transaction:\n"++).show) $ ptransaction p)
                  (show p)
+                 assertedcomm
                  (showMixedAmount assertedbal)
                  (showMixedAmount singlebal)
 

hledger-lib/Hledger/Read/JournalReader.hs

@@ -513,7 +513,7 @@ postingp = do
   account <- modifiedaccountname
   let (ptype, account') = (accountNamePostingType account, unbracket account)
   amount <- spaceandamountormissing
-  massertion <- balanceassertion
+  massertion <- partialbalanceassertion
   _ <- fixedlotprice
   many spacenonewline
   ctx <- getState
@@ -720,8 +720,8 @@ priceamount =
             return $ UnitPrice a))
          <|> return NoPrice
 
-balanceassertion :: GenParser Char JournalContext (Maybe MixedAmount)
-balanceassertion =
+partialbalanceassertion :: GenParser Char JournalContext (Maybe MixedAmount)
+partialbalanceassertion =
     try (do
           many spacenonewline
           char '='
@@ -730,6 +730,16 @@ balanceassertion =
           return $ Just $ Mixed [a])
          <|> return Nothing
 
+-- balanceassertion :: GenParser Char JournalContext (Maybe MixedAmount)
+-- balanceassertion =
+--     try (do
+--           many spacenonewline
+--           string "=="
+--           many spacenonewline
+--           a <- amountp -- XXX should restrict to a simple amount
+--           return $ Just $ Mixed [a])
+--          <|> return Nothing
+
 -- http://ledger-cli.org/3.0/doc/ledger3.html#Fixing-Lot-Prices
 fixedlotprice :: GenParser Char JournalContext (Maybe Amount)
 fixedlotprice =