lib: Calculate value at posting date for register --value=then -M.

hledger-lib/Hledger/Reports/MultiBalanceReport.hs

@@ -560,14 +560,6 @@ subtractAcct :: Account -> Account -> Account
 subtractAcct a@Account{aibalance=i1,aebalance=e1} Account{aibalance=i2,aebalance=e2} =
     a{aibalance = i1 - i2, aebalance = e1 - e2}
 
--- | Whether the market price for postings might change when reported in
--- different report periods.
-changingValuation :: ReportOpts -> Bool
-changingValuation ropts = case value_ ropts of
-    Just (AtCost (Just _)) -> True
-    Just (AtEnd  _)        -> True
-    _                      -> False
-
 -- | Extract period changes from a cumulative list
 periodChanges :: Account -> Map k Account -> Map k Account
 periodChanges start amtmap =

hledger-lib/Hledger/Reports/PostingsReport.hs

@@ -80,12 +80,12 @@ postingsReport rspec@ReportSpec{rsOpts=ropts@ReportOpts{..}} j = items
 
       -- Postings, or summary postings with their subperiod's end date, to be displayed.
       displayps :: [(Posting, Maybe Day)]
-        | multiperiod =
-            let summaryps = summarisePostingsByInterval interval_ whichdate mdepth showempty reportspan reportps
-            in [(pvalue lastday p, Just periodend) | (p, periodend) <- summaryps, let lastday = addDays (-1) periodend]
-        | otherwise =
-            [(pvalue reportorjournallast p, Nothing) | p <- reportps]
+        | multiperiod && changingValuation ropts = [(pvalue lastday p, Just periodend) | (p, periodend) <- summariseps reportps, let lastday = addDays (-1) periodend]
+        | multiperiod                            = [(p, Just periodend) | (p, periodend) <- summariseps valuedps]
+        | otherwise                              = [(p, Nothing)        | p <- valuedps]
         where
+          summariseps = summarisePostingsByInterval interval_ whichdate mdepth showempty reportspan
+          valuedps = map (pvalue reportorjournallast) reportps
           showempty = empty_ || average_
           reportorjournallast =
             fromMaybe (error' "postingsReport: expected a non-empty journal") $  -- PARTIAL: shouldn't happen

hledger-lib/Hledger/Reports/ReportOptions.hs

@@ -23,6 +23,7 @@ module Hledger.Reports.ReportOptions (
   rawOptsToReportSpec,
   flat_,
   tree_,
+  changingValuation,
   reportOptsToggleStatus,
   simplifyStatuses,
   whichDateFromOpts,
@@ -471,6 +472,14 @@ queryFromFlags ReportOpts{..} = simplifyQuery $ And flagsq
     consIf f b = if b then (f True:) else id
     consJust f = maybe id ((:) . f)
 
+-- | Whether the market price for postings might change when reported in
+-- different report periods.
+changingValuation :: ReportOpts -> Bool
+changingValuation ropts = case value_ ropts of
+    Just (AtCost (Just _)) -> True
+    Just (AtEnd  _)        -> True
+    _                      -> False
+
 -- Report dates.
 
 -- | The effective report span is the start and end dates specified by

hledger/test/journal/valuation.test

@@ -603,8 +603,8 @@ $ hledger -f- reg --value=then -b 2020-03 -H
 2020-04-01                      (a)                            4 B          10 B
 >=0
 
-# 52. --value=then with a report interval. How are the summary amounts valued ?
-# Currently each interval's unvalued sum is valued on its first day.
+# 52. --value=then with a report interval. Summary amounts are the sums of the
+# values of each posting at their posting date.
 <
 P 2020-01-01 A 1 B
 P 2020-02-01 A 2 B
@@ -624,8 +624,8 @@ P 2020-04-01 A 4 B
    (a)  1 A
 
 $ hledger -f- reg --value=then -Q
-2020Q1                  a                                      3 B           3 B
-2020Q2                  a                                      4 B           7 B
+2020Q1                  a                                      6 B           6 B
+2020Q2                  a                                      4 B          10 B
 >=0
 
 # 53. print --value should affect all postings, including when there's an implicit transaction price