fix: bal: budget goals were ignoring rule-specified start date

hledger-lib/Hledger/Reports/BudgetReport.hs

@@ -26,7 +26,7 @@ import Data.Decimal (roundTo)
 import Data.Function (on)
 import Data.HashMap.Strict (HashMap)
 import qualified Data.HashMap.Strict as HM
-import Data.List (find, partition, transpose, foldl')
+import Data.List (find, partition, transpose, foldl', maximumBy)
 import Data.List.Extra (nubSort)
 import Data.Maybe (fromMaybe, catMaybes, isJust)
 import Data.Map (Map)
@@ -36,7 +36,7 @@ import Data.Text (Text)
 import qualified Data.Text as T
 import qualified Data.Text.Lazy as TL
 import qualified Data.Text.Lazy.Builder as TB
-import Safe (maximumDef, minimumDef)
+import Safe (minimumDef)
 --import System.Console.CmdArgs.Explicit as C
 --import Lucid as L
 import qualified Text.Tabular.AsciiWide as Tab
@@ -46,6 +46,7 @@ import Hledger.Utils
 import Hledger.Reports.ReportOptions
 import Hledger.Reports.ReportTypes
 import Hledger.Reports.MultiBalanceReport
+import Data.Ord (comparing)
 
 
 type BudgetGoal    = Change
@@ -113,19 +114,34 @@ journalAddBudgetGoalTransactions bopts ropts reportspan j =
       where
         mbudgetgoalsstartdate =
           -- We want to also generate budget goal txns before the report start date, in case -H is used.
-          -- What should the actual starting date for goal txns be ? This gets a little tricky: consider a
+          -- What should the actual starting date for goal txns be ? This gets tricky. 
-          -- journal with a "~ monthly" periodic transaction rule, where the first transaction is on 1/5.
+          -- Consider a journal with a "~ monthly" periodic transaction rule, where the first transaction is on 1/5.
           -- Users will certainly expect a budget goal for january, but "~ monthly" generates transactions
           -- on the first of month, and starting from 1/5 would exclude 1/1.
-          -- Hopefully the following procedure will produce intuitive behaviour in general:
+          -- Secondly, consider a rule like "~ every february 2nd from 2020/01"; we should not start that
+          -- before 2020-02-02.
+          -- Hopefully the following algorithm produces intuitive behaviour in general:
           -- from the earlier of the journal start date and the report start date,
           -- move backward to the nearest natural start date of the largest period seen among the
-          -- active periodic transactions (so here: monthly, 1/5 -> 1/1).
+          -- active periodic transactions, unless that is disallowed by a start date in the periodic rule.
+          -- (Do we need to pay attention to an end date in the rule ? Don't think so.)
+          -- (So with "~ monthly", the journal start date 1/5 is adjusted to 1/1.)
           case minimumDef Nothing $ filter isJust [journalStartDate False j, spanStart reportspan] of
             Nothing -> Nothing
-            Just d  -> Just $ intervalStartBefore biggestinterval d
+            Just d  -> Just d'
               where
-                biggestinterval = maximumDef (Days 1) $ map ptinterval budgetpts
+                -- the interval and any date span of the periodic transaction with longest period
+                (interval, span) =
+                  case budgetpts of
+                    []  -> (Days 1, nulldatespan)
+                    pts -> (ptinterval pt, ptspan pt)
+                      where pt = maximumBy (comparing ptinterval) pts  -- PARTIAL: maximumBy won't fail
+                -- the natural start of this interval on or before the journal/report start
+                intervalstart = intervalStartBefore interval d
+                -- the natural interval start before the journal/report start,
+                -- or the rule-specified start if later,
+                -- but no later than the journal/report start.
+                d' = min d $ maybe intervalstart (max intervalstart) $ spanStart span
 
     -- select periodic transactions matching a pattern
     -- (the argument of the (final) --budget option).

hledger/test/balance/budget.test

@@ -620,7 +620,7 @@ Budget performance in 2020Q1:
 ---------------++-----------------------------------------------------------
                ||     0 [ 0% of $500]  0 [0% of $500]      0 [  0% of $500] 
 
-# 32. Select from multiple named budgets.
+# 32, 33. Select from multiple named budgets.
 <
 ~ weekly   weekly budget
   (aaa)   1
@@ -636,7 +636,7 @@ $ hledger -f- bal --budget=monthly -p 2021-01
 > !/aaa/
 >=
 
-# 33. Cumulative budget report.
+# 34. Cumulative budget report.
 <
 ~ monthly
   (a)  10
@@ -656,8 +656,8 @@ Budget performance in 2022-01-01..2022-02-28:
 ---++---------------------------------
    || 10 [100% of 10]  15 [75% of 20] 
 
-# 34. Historical budget report.
+# 35. Historical budget report.
-$ hledger -f- bal --budget -M --historical -b 2022-02-01
+$ hledger -f- bal --budget -MH -b 2022-02-01
 Budget performance in 2022-02:
 
    ||     2022-02-28 
@@ -665,3 +665,17 @@ Budget performance in 2022-02:
  a || 15 [75% of 20] 
 ---++----------------
    || 15 [75% of 20] 
+
+# 36. Historical budget report where the periodic transaction has date bounds.
+<
+~ every february 2nd from 2020/01
+    (a)  1
+
+$ hledger -f- bal --budget -MH -p 2020q1
+Budget performance in 2020Q1:
+
+   || 2020-01-31   2020-02-29   2020-03-31 
+===++======================================
+ a ||      0 [0]  0 [0% of 1]  0 [0% of 1] 
+---++--------------------------------------
+   ||      0 [0]  0 [0% of 1]  0 [0% of 1]