fix: balance: Show all empty accounts in flat balance reports. (#1688)

Previously we only showed empty leaves.

hledger-lib/Hledger/Reports/MultiBalanceReport.hs

@@ -410,12 +410,17 @@ displayedAccounts ReportSpec{_rsQuery=query,_rsReportOpts=ropts} valuedaccts
     -- Accounts interesting for their own sake
     isInteresting name amts =
         d <= depth                                 -- Throw out anything too deep
-        && ((empty_ ropts && all (null . asubs) amts)  -- Keep all leaves when using empty_
-           || not (isZeroRow balance amts))            -- Throw out anything with zero balance
+        && ( (empty_ ropts && keepWhenEmpty amts)  -- Keep empty accounts when called with --empty
+           || not (isZeroRow balance amts)         -- Keep everything with a non-zero balance in the row
+           )
       where
         d = accountNameLevel name
-        balance | ALTree <- accountlistmode_ ropts, d == depth = maybeStripPrices . aibalance
-                | otherwise = maybeStripPrices . aebalance
+        keepWhenEmpty = case accountlistmode_ ropts of
+            ALFlat -> const True          -- Keep all empty accounts in flat mode
+            ALTree -> all (null . asubs)  -- Keep only empty leaves in tree mode
+        balance = maybeStripPrices . case accountlistmode_ ropts of
+            ALTree | d == depth -> aibalance
+            _                   -> aebalance
           where maybeStripPrices = if show_costs_ ropts then id else mixedAmountStripPrices
 
     -- Accounts interesting because they are a fork for interesting subaccounts

hledger/test/balance/no-total-no-elide.test

@@ -21,7 +21,7 @@ $ hledger -f - balance
   (a:b)   1
 
 # 2. An uninteresting parent account (with same balance as its single subaccount) is elided by default, like ledger
-$ hledger -f - balance --no-total
+$ hledger -f - balance --no-total --tree
 >
                    1  a:b
 >=0
@@ -98,3 +98,19 @@ Balance changes in 2020:
  a       ||    1 
    aa    ||    0 
      aaa ||    0 
+
+# 11. In flat mode, display all zero-balance accounts, including non-leaves
+$ hledger -f - balance --flat --no-total --empty
+                   1  a
+                   0  a:aa
+                   0  a:aa:aaa
+
+# 12. Same as 11 for multiperiod
+$ hledger -f - balance --flat --no-total -Y --empty
+Balance changes in 2020:
+
+          || 2020 
+==========++======
+ a        ||    1 
+ a:aa     ||    0 
+ a:aa:aaa ||    0