lib: roi does not fail on empty input data (+test)

hledger/Hledger/Cli/Commands/Roi.hs

@@ -148,7 +148,8 @@ timeWeightedReturn showCashFlow prettyTables investmentsQuery trans (OneSpan spa
           cashflow
 
   let finalUnitBalance = if null units then initialUnits else let (_,_,_,u) = last units in u
-      finalUnitPrice = valueAfter / finalUnitBalance
+      finalUnitPrice = if finalUnitBalance == 0 then initialUnitPrice
+                       else valueAfter / finalUnitBalance
       totalTWR = roundTo 2 $ (finalUnitPrice - initialUnitPrice)
       years = fromIntegral (diffDays spanEnd spanBegin) / 365 :: Double
       annualizedTWR = 100*((1+(realToFrac totalTWR/100))**(1/years)-1) :: Double
@@ -202,6 +203,9 @@ internalRateOfReturn showCashFlow prettyTables (OneSpan spanBegin spanEnd valueB
        (map ((:[]) . show) amounts))
 
   -- 0% is always a solution, so require at least something here
+  case totalCF of
+    [] -> return 0
+    _ -> 
       case ridders
 #if MIN_VERSION_math_functions(0,3,0)
         (RiddersParam 100 (AbsTol 0.00001))

tests/roi.test

@@ -210,3 +210,18 @@ hledger -f- roi --inv investment --pnl pnl -b 2017-06 -e 2018
 +---++------------+------------++---------------+----------+-------------+-----++-------+--------+
 
 >>>=0
+
+# 8. Dont fail where there is no rate-of-return 
+hledger -f- roi -p 2019-11
+<<<
+2019/11/01 Example
+  Assets:Checking  1
+  Income:Salary  -1
+>>>
++---++------------+------------++---------------+----------+-------------+-----++-------+-------+
+|   ||      Begin |        End || Value (begin) | Cashflow | Value (end) | PnL ||   IRR |   TWR |
++===++============+============++===============+==========+=============+=====++=======+=======+
+| 1 || 2019/11/01 | 2019/11/30 ||             0 |        0 |           0 |   0 || 0.00% | 0.00% |
++---++------------+------------++---------------+----------+-------------+-----++-------+-------+
+
+>>>=0