lib: disallow prices in balance assertions/assignments (fix #824)

(and in Ledger-style {=FIXEDLOTPRICES} )

hledger-lib/Hledger/Read/Common.hs

@@ -721,7 +721,7 @@ priceamountp = option NoPrice $ do
   priceConstructor <- char '@' *> pure TotalPrice <|> pure UnitPrice
 
   lift (skipMany spacenonewline)
-  priceAmount <- amountwithoutpricep <?> "amount (as a price)"
+  priceAmount <- amountwithoutpricep <?> "unpriced amount (specifying a price)"
 
   pure $ priceConstructor priceAmount
 
@@ -731,14 +731,17 @@ balanceassertionp = do
   char '='
   exact <- optional $ try $ char '='
   lift (skipMany spacenonewline)
-  a <- amountp <?> "amount (for a balance assertion or assignment)" -- XXX should restrict to a simple amount
+  a <- amountwithoutpricep <?> "unpriced amount (for a balance assertion or assignment)"
   return BalanceAssertion
     { baamount = a
     , baexact = isJust exact
     , baposition = sourcepos
     }
 
--- http://ledger-cli.org/3.0/doc/ledger3.html#Fixing-Lot-Prices
+-- Parse a Ledger-style fixed lot price: {=PRICE}
+-- https://www.ledger-cli.org/3.0/doc/ledger3.html#Fixing-Lot-Prices .
+-- Currently we ignore these (hledger's @ PRICE is equivalent),
+-- and we don't parse a Ledger-style {PRICE} (equivalent to Ledger's @ PRICE).
 fixedlotpricep :: JournalParser m (Maybe Amount)
 fixedlotpricep = optional $ do
   try $ do
@@ -747,7 +750,7 @@ fixedlotpricep = optional $ do
   lift (skipMany spacenonewline)
   char '='
   lift (skipMany spacenonewline)
-  a <- amountp -- XXX should restrict to a simple amount
+  a <- amountwithoutpricep <?> "unpriced amount (for an ignored ledger-style fixed lot price)"
   lift (skipMany spacenonewline)
   char '}'
   return a

hledger-lib/hledger_journal.m4.md

@@ -436,6 +436,11 @@ One workaround is to isolate each commodity into its own subaccount:
   a:euro   0 ==  1€
 ```
 
+### Assertions and prices
+
+Balance assertion (or assignment) amounts should not have a [price](#transaction-prices),
+as the meaning of that would be unclear.
+
 ### Assertions and subaccounts
 
 Balance assertions do not count the balance from subaccounts; they check

tests/journal/balance-assertions.test

@@ -356,3 +356,12 @@ hledger -f - stats
 >>> /Transactions/
 >>>2
 >>>=0
+
+# 20. Balance assertions may not have a price in them.
+hledger -f- stats
+<<<
+2019/01/01
+    (a)             1A = 1A @ 2B
+>>>
+>>>2 /unexpected '@'/
+>>>=1