journal: default commodity (D) limits display precision too (#1187)

D directives are now fully equivalent to commodity directives for
setting a commodity's display style. (Previously it was equivalent to
a posting amount, so it couldn't limit the number of decimal places.)
When both kinds of directive exist, commodity directives take precedence.
When there are multiple D directives in the journal, only the last one
affects display style.

hledger-lib/Hledger/Data/Journal.hs

@@ -921,15 +921,20 @@ journalApplyCommodityStyles j@Journal{jtxns=ts, jpricedirectives=pds} =
         fixbalanceassertion ba = ba{baamount=styleAmount styles $ baamount ba}
         fixpricedirective pd@PriceDirective{pdamount=a} = pd{pdamount=styleAmountExceptPrecision styles a}
 
--- | Get all the amount styles defined in this journal, either declared by
--- a commodity directive or inferred from amounts, as a map from symbol to style.
--- Styles declared by commodity directives take precedence, and these also are
--- guaranteed to know their decimal point character.
+-- | Get the canonical amount styles for this journal, whether
+-- declared by commodity directives, by the last default commodity (D)
+-- directive, or inferred from posting amounts, as a map from symbol
+-- to style. Styles declared by directives take precedence (and
+-- commodity takes precedence over D). Styles from directives are
+-- guaranteed to specify the decimal mark character.
 journalCommodityStyles :: Journal -> M.Map CommoditySymbol AmountStyle
-journalCommodityStyles j = declaredstyles <> inferredstyles
+journalCommodityStyles j =
+  -- XXX could be some redundancy here, cf journalStyleInfluencingAmounts
+  commoditystyles <> defaultcommoditystyle <> inferredstyles
   where
-    declaredstyles = M.mapMaybe cformat $ jcommodities j
-    inferredstyles = jinferredcommodities j
+    commoditystyles       = M.mapMaybe cformat $ jcommodities j
+    defaultcommoditystyle = M.fromList $ catMaybes [jparsedefaultcommodity j]
+    inferredstyles        = jinferredcommodities j
 
 -- | Collect and save inferred amount styles for each commodity based on
 -- the posting amounts in that commodity (excluding price amounts), ie:

tests/journal/default-commodity.test

@@ -56,19 +56,16 @@ $ hledger -f- print
 
 >=0
 
-# 5. commodity and display style applied to the second posting amount..
-# which ends up setting the digit group style, since it's the first amount
-# with digit groups. The great precision is used.
+# 5. A D directive affects all aspects of display style, 
+# including limiting the display precision, like a commodity directive (#1187).
 <
-D $1,000.0
-2010/1/1
-  (a)  $1000000.00
-  (b)   1000000
+D 1,000.0 A
+1/1
+  (a)  1000.123
 
 $ hledger -f- print
-2010-01-01
-    (a)    $1,000,000.00
-    (b)    $1,000,000.00
+2020-01-01
+    (a)       1,000.1 A
 
 >=0