fix balance accumulation across assertions (#195)

A sequence of balance assertions asserting first one commodity, then
another, then the first again, was not working.

hledger-lib/Hledger/Data/Journal.hs

@@ -446,10 +446,9 @@ checkBalanceAssertion :: ([String],MixedAmount) -> [Posting] -> ([String],MixedA
 checkBalanceAssertion (errs,startbal) ps
   | null ps = (errs,startbal)
   | isNothing assertion = (errs,startbal)
-  |
-    -- bal' /= assertedbal  -- MixedAmount's Eq instance currently gets confused by different precisions
-    not $ isReallyZeroMixedAmount (bal - assertedbal) = (errs++[err], bal)
-  | otherwise = (errs,bal)
+  | -- bal' /= assertedbal  -- MixedAmount's Eq instance currently gets confused by different precisions
+    not $ isReallyZeroMixedAmount (bal - assertedbal) = (errs++[err], fullbal)
+  | otherwise = (errs,fullbal)
   where
     p = last ps
     assertion = pbalanceassertion p
@@ -473,7 +472,7 @@ checkBalanceAssertion (errs,startbal) ps
 -- assertion are discarded.
 splitAssertions :: [Posting] -> [[Posting]]
 splitAssertions ps
-  | null rest = [[]]
+  | null rest = []
   | otherwise = (ps'++[head rest]):splitAssertions (tail rest)
   where
     (ps',rest) = break (isJust . pbalanceassertion) ps

tests/journal/balance-assertions.test

@@ -101,7 +101,20 @@ hledgerdev -f - stats
 >>>2
 >>>=0
 
-# 7. what should happen here ? Currently,
+# 7. balances should accumulate (#195)
+hledgerdev -f - stats
+<<<
+1/1
+    (a)   1F = 1F
+    (a)   2G = 2G
+
+1/2
+    (a)   3F = 4F
+>>> !/assertion failed/
+>>>2
+>>>=0
+
+# 8. what should happen here ? Currently,
 # in a, 3.4 EUR @@ $5.6 and -3.4 EUR cancel out (wrong ?)
 # in b, 
 #