fix: print: don't round in implicit conversions (fix #2079)

hledger-lib/Hledger/Data/Journal.hs

@@ -793,13 +793,14 @@ journalModifyTransactions verbosetags d j =
     Left err -> Left err
 
 -- | Choose and apply a consistent display style to the posting
--- amounts in each commodity (see journalCommodityStyles).
+-- amounts in each commodity (see journalCommodityStyles),
+-- keeping all display precisions unchanged.
 -- Can return an error message eg if inconsistent number formats are found.
 journalApplyCommodityStyles :: Journal -> Either String Journal
 journalApplyCommodityStyles = fmap fixjournal . journalInferCommodityStyles
   where
     fixjournal j@Journal{jpricedirectives=pds} =
-        journalMapPostings (postingApplyCommodityStyles styles) j{jpricedirectives=map fixpricedirective pds}
+        journalMapPostings (postingApplyCommodityStylesExceptPrecision styles) j{jpricedirectives=map fixpricedirective pds}
       where
         styles = journalCommodityStyles j
         fixpricedirective pd@PriceDirective{pdamount=a} = pd{pdamount=amountSetStylesExceptPrecision styles a}

hledger/Hledger/Cli/Commands/Print.hs

@@ -74,7 +74,7 @@ printEntries opts@CliOpts{reportspec_=rspec} j =
   styleAmounts styles $
   entriesReport rspec j
   where
-    styles = journalCommodityStyles j
+    styles = M.map amountStyleUnsetPrecision $ journalCommodityStyles j  -- keep all precisions unchanged
     fmt = outputFormatFromOpts opts
     render | fmt=="txt"  = entriesReportAsText opts
            | fmt=="csv"  = printCSV . entriesReportAsCsv

hledger/test/print/print-style.test

@@ -0,0 +1,75 @@
+# print amount styling tests
+#
+# The amounts are:
+#  amt     - the posting amount
+#  cost    - the posting amount's cost
+#  bal     - the balance assertion amount
+#  balcost - the balance assertion amount's cost
+#
+# Styling includes:
+#  basic - everything except precision
+#  prec  - precision (number of decimal places)
+#
+# Historical behaviour:
+# | hledger | amt basic | cost basic | bal basic | balcost basic | amt prec | cost prec | bal prec | balcost prec |
+# | 1.14    | Y         | N          | N         | N             | Y        | N         | N        | N            |
+# | 1.22    | Y         | N          | Y         | N             | N        | N         | N        | N            |
+# | 1.30    | Y         | Y          | Y         | N             | N        | N         | N        | N            |
+# | 1.31    | Y         | Y          | Y         | Y             | N        | N         | N        | N            |
+#
+# In the following,
+#  basic styling will move the commodity symbol to the left
+#  precision styling will hide the decimal place
+
+# 1. print styles all amounts, but leaves all precisions unchanged, even with -c.
+<
+commodity A 1000.
+commodity B 1000.
+
+2023-01-01
+    (a)    1.2 A @ 3.4 B = 1.2 A @ 3.4 B
+	
+$ hledger -f- print -c A1000.00 -c B1000.00
+2023-01-01
+    (a)     A1.2 @ B3.4 = A1.2 @ B3.4
+
+>=
+
+# 2. Precisions are also preserved when there's an implicit conversion (#2079).
+<
+commodity A 1000.
+
+2023-01-01
+    f       A 1.5
+    g       A 1.5
+    c      B -3
+
+$ hledger -f- print
+2023-01-01
+    f           A 1.5
+    g           A 1.5
+    c            B -3
+
+>=
+
+
+# Maybe later:
+
+# # 0. With print, -c has extra power: it can increase all amount precisions.
+# $ hledger -f- print -c A1000.00 -c B1000.00
+# 2023-01-01
+#     (a)    A1.20 @ B3.40 = A1.20 @ B3.40
+# 
+# >=
+# 
+# # 0. And -c can decrease trailing decimal zeros. But not significant decimal digits
+# (because that would change transactions).
+# <
+# 2023-01-01
+#     (a)    1.2340 A @ 3.4560 B = 1.234 A @ 3.456 B
+#
+# $ hledger -f- print -c A1000. -c B1000.
+# 2023-01-01
+#     (a)    A1.234 @ B3.456 = A1.234 @ B3.456
+# 
+# >=