;valuation: more tests; document default amount style issue

[ci skip]

hledger-lib/Hledger/Data/Valuation.hs

@@ -81,13 +81,23 @@ amountApplyValuation prices styles periodend today ismultiperiod v a =
 -- given valuation date. (The default valuation commodity is the
 -- commodity of the latest applicable market price before the
 -- valuation date.)
+--
+-- The returned amount will have its commodity's canonical style applied,
+-- but with the precision adjusted to show all significant decimal digits
+-- up to a maximum of 8. (experimental)
+--
 -- If the market prices available on that date are not sufficient to
 -- calculate this value, the amount is left unchanged.
 amountValueAtDate :: [PriceDirective] -> M.Map CommoditySymbol AmountStyle -> Maybe CommoditySymbol -> Day -> Amount -> Amount
 amountValueAtDate pricedirectives styles mto d a =
   case priceLookup pricedirectives d (acommodity a) mto of
     Nothing           -> a
-    Just (comm, rate) -> styleAmount styles $ amount{acommodity=comm, aquantity=rate * aquantity a}
+    Just (comm, rate) ->
+      -- setNaturalPrecisionUpTo 8 $  -- XXX force higher precision in case amount appears to be zero ?
+                                      -- Make default display style use precision 2 instead of 0 ?
+                                      -- Leave as is for now; mentioned in manual.
+      styleAmount styles
+      amount{acommodity=comm, aquantity=rate * aquantity a}
 
 ------------------------------------------------------------------------------
 -- Building a price graph

hledger/hledger_options.m4.md

@@ -644,6 +644,42 @@ $ hledger -f- print --value=2000-01-15
 
 ```
 
+You may need to explicitly set a commodity's display style, when reverse prices are used.
+Eg this output might be surprising:
+```
+P 2000-01-01 A 2B
+
+2000-01-01
+  a  1B
+  b
+```
+```
+$ hledger print -x -X A
+2000/01/01
+    a               0
+    b               0
+
+```
+Explanation: because there's no amount or commodity directive specifying a display style
+for A, 0.5A gets the default style, which shows no decimal digits. Because the displayed
+amount looks like zero, the commodity symbol and minus sign are not displayed either.
+Adding a commodity directive sets a more useful display style for A:
+```
+P 2000-01-01 A 2B
+commodity 0.00A
+
+2000-01-01
+  a  1B
+  b
+```
+```
+$ hledger print -X A
+2000/01/01
+    a           0.50A
+    b          -0.50A
+
+```
+
 #### Effect of --value on reports
 
 Below is how `--value` affects each of hledger's reports, currently.

tests/journal/valuation2.test

@@ -0,0 +1,102 @@
+; More valuation tests. See also tests/journal/valuation.test.
+
+; some market prices
+P 2019-01-01 B   10 A
+P 2019-01-01 C    2 B
+P 2019-01-01 A  100 D
+P 2019-01-01 E    3 D
+
+; a transaction with both amounts in B
+2019-06-01
+    a  1 B
+    b
+
+; tests follow. This comment directive makes this file readable
+; by hledger, as well as shelltest; useful when troubleshooting.
+comment
+
+# 1. normal unvalued output
+$ hledger -f- print -x
+2019/06/01
+    a             1 B
+    b            -1 B
+
+>=
+
+# 2. current market value in default valuation commodity
+$ hledger -f- print -x -V
+2019/06/01
+    a            10 A
+    b           -10 A
+
+>=
+
+# 3. same as above, but request commodity A explicitly
+$ hledger -f- print -x --value=now,A
+2019/06/01
+    a            10 A
+    b           -10 A
+
+>=
+
+# 4. request commodity B - no effect
+$ hledger -f- print -x --value=now,B
+2019/06/01
+    a             1 B
+    b            -1 B
+
+>=
+
+# 5. request commodity we don't have prices for - no effect
+$ hledger -f- print -x --value=now,Z
+2019/06/01
+    a             1 B
+    b            -1 B
+
+>=
+
+# 6. request commodity C - uses reverse of C->B price.
+# There's nothing setting C display style, so the default style is used,
+# which shows no decimal digits.
+# And because that makes it display as zero, the commodity symbol
+# and sign are not shown either.
+$ hledger -f- print -x --value=now,C
+2019/06/01
+    a               0
+    b               0
+
+>=
+# # There's nothing setting C display style, so the default style is used,
+# # but the precision is increased to show the decimal digit
+# # (otherwise it would show C0).
+# $ hledger -f- print -x --value=now,C
+# 2019/06/01
+#     a            C0.5
+#     b           C-0.5
+#
+# >=
+
+# 7. request commodity D - chains B->A, A->D prices
+$ hledger -f- print -x --value=now,D
+2019/06/01
+    a          1000 D
+    b         -1000 D
+
+>=
+
+# 8. request commodity E - chains B->A, A->D, reverse of D->E prices.
+# As with C above, E gets the default display style, with precision 0.
+$ hledger -f- print -x --value=now,E
+2019/06/01
+    a            E333
+    b           E-333
+
+>=
+# # As with C above, E gets the default display style, but with the precision
+# # increased to show the decimal digits, but no more than 8.
+# $ hledger -f- print -x --value=now,E
+# 2019/06/01
+#     a     E333.33333333
+#     b    E-333.33333333
+#
+# >=