imp:print:beancount: remove redundant conversion postings automatically

hledger/Hledger/Cli/Commands/Print.hs

@@ -44,6 +44,7 @@ import Hledger.Cli.Utils
 import Hledger.Cli.Anchor (setAccountAnchor)
 import qualified Lucid
 import qualified System.IO as IO
+import Data.Maybe (isJust)
 
 printmode = hledgerCommandMode
   $(embedFileRelative "Hledger/Cli/Commands/Print.txt")
@@ -186,17 +187,33 @@ entriesReportAsTextHelper showtxn = TB.toLazyText . foldMap (TB.fromText . showt
 entriesReportAsBeancount :: EntriesReport -> TL.Text
 entriesReportAsBeancount ts =
   -- PERF: gathers and converts all account names, then repeats that work when showing each transaction
-  opendirectives <> "\n" <> entriesReportAsTextHelper showTransactionBeancount allrealts
+  opendirectives <> "\n" <> entriesReportAsTextHelper showTransactionBeancount ts3
   where
-    allrealts = [t{tpostings=filter isReal $ tpostings t} | t <- ts]
+    -- Remove any virtual postings.
+    ts2 = [t{tpostings=filter isReal $ tpostings t} | t <- ts]
+
+    -- Remove any conversion postings that are redundant with costs.
+    -- It would be easier to remove the costs instead,
+    -- but those are more useful to Beancount than conversion postings.
+    ts3 =
+      [ t{tpostings=filter (not . isredundantconvp) $ tpostings t}
+      | t <- ts2
+      -- XXX But how to do it ? conversion-posting tag is on non-redundant postings too.
+      -- Assume the simple case of no more than one cost + conversion posting group in each transaction.
+      -- Actually that seems to be required by hledger right now.
+      , let isredundantconvp p =
+              matchesPosting (Tag (toRegex' "conversion-posting") Nothing) p
+              && any (any (isJust.acost) . amounts . pamount) (tpostings t)
+      ]
+
     opendirectives
       | null ts = ""
       | otherwise = TL.fromStrict $ T.unlines [
           firstdate <> " open " <> accountNameToBeancount a
-          | a <- nubSort $ concatMap (map paccount.tpostings) allrealts
+          | a <- nubSort $ concatMap (map paccount.tpostings) ts3
           ]
         where
-          firstdate = showDate $ minimumDef err $ map tdate allrealts
+          firstdate = showDate $ minimumDef err $ map tdate ts3
             where err = error' "entriesReportAsBeancount: should not happen"
 
 entriesReportAsSql :: EntriesReport -> TL.Text

hledger/hledger.m4.md

@@ -830,12 +830,14 @@ using various utilities like `libreoffice --headless` or
 This is [Beancount's journal format][beancount journal].
 You can use this to export your hledger data to [Beancount],
 perhaps to query it with [Beancount Query Language] or with the [Fava] web app.
+
 hledger will try to adjust your data to suit Beancount.
-If you plan to export often, you may want to follow Beancount's conventions in your hledger data,
-to ease conversion. Eg use Beancount-friendly account names, currency codes instead of currency symbols,
-and avoid virtual postings, redundant cost notation, etc.
-Here are more details
-(see also "hledger and Beancount" <https://hledger.org/beancount.html>).
+You should be cautious and check the conversion carefully until you are confident it is good.
+If you plan to export to Beancount often, you may want to follow its conventions in your hledger data, to make conversion easier.
+Eg use Beancount-friendly account names, currency codes instead of currency symbols, costs instead of equity conversion postings, no virtual postings, etc.
+
+Here are more details.
+<!-- (see also "hledger and Beancount" <https://hledger.org/beancount.html>). -->
 
 #### Beancount account names
 
@@ -866,8 +868,9 @@ if you have any, they will not appear in beancount output.
 
 #### Beancount costs
 
-Beancount doesn't allow [redundant cost notation](https://hledger.org/hledger.html#combining-costs-and-equity-conversion-postings)
-as hledger does. If you have entries like this, you will need to comment out either the costs or the equity postings.
+Beancount doesn't allow [redundant costs and conversion postings](https://hledger.org/hledger.html#combining-costs-and-equity-conversion-postings) as hledger does.
+If you have entries like this, the conversion postings will be dropped.
+Currently we support at most one cost + conversion postings group per transaction.
 
 #### Beancount operating currency
 

hledger/test/print/beancount.test

@@ -59,3 +59,63 @@ $ hledger -f- print -O beancount
     Assets:A           0 USD
 
 >=
+
+# ** 5. Conversion postings that are not redundant are preserved.
+# If the accounts are named after currency symbols, they will look strange.
+# (A better conversion would be this, but it seems hard to automate:
+#  Equity:Conversion:EUR-USD:USD, Equity:Conversion:EUR-USD:EUR.)
+<
+2000-01-01
+    Assets                      $1
+    equity:conversion:€-$:$    -$1
+    equity:conversion:€-$:€     €1
+    Assets                     €-1
+
+$ hledger -f- print -O beancount
+2000-01-01 open Assets:A
+2000-01-01 open Equity:Conversion:C20ac-C24:C24
+2000-01-01 open Equity:Conversion:C20ac-C24:C20ac
+
+2000-01-01 *
+    Assets:A                                    1 USD
+    Equity:Conversion:C20ac-C24:C24            -1 USD
+    Equity:Conversion:C20ac-C24:C20ac           1 EUR
+    Assets:A                                   -1 EUR
+
+>=
+
+# ** 6. Conversion postings that are redundant with costs are dropped.
+<
+2000-01-01
+    Assets                      $1 @@ €1
+    equity:conversion:€-$:$    -$1
+    equity:conversion:€-$:€     €1
+    Assets                     €-1
+
+$ hledger -f- print -O beancount
+2000-01-01 open Assets:A
+
+2000-01-01 *
+    Assets:A    1 USD @@ 1 EUR
+    Assets:A            -1 EUR
+
+>=
+
+# ** 7. Multiple cost/conversion groups within a transaction are not supported
+# (by hledger generally, apparently ?)
+<
+2000-01-01
+    Assets                      $1 @@ €1
+    equity:conversion:€-$:$    -$1
+    equity:conversion:€-$:€     €1
+    Assets                     €-1
+    ;
+    Assets                      A1 @@ B1
+    equity:conversion:€-$:$    -A1
+    equity:conversion:€-$:€     B1
+    Assets                     B-1
+
+$ hledger -f- print -O beancount
+>2 /unbalanced/
+>=1
+