fmt: do not remove trailing zeros for %g and %G with #(sharp) flag

Fixes #36562

Change-Id: Id98ae9f7362cfb825b306c36649d505692d6d60e
GitHub-Last-Rev: 405d51b12eb04da8cc3559c92f1546e69a8c1a19
GitHub-Pull-Request: golang/go#36588
Reviewed-on: https://go-review.googlesource.com/c/go/+/215001
Reviewed-by: Rob Pike <r@golang.org>

diff --git a/src/fmt/fmt_test.go b/src/fmt/fmt_test.go
index 072fc6bf3b4dd8292c667e119b676f0957cc2b84..6004061020577cbf21bbc6c89648432f099ec70c 100644 (file)
--- a/src/fmt/fmt_test.go
+++ b/src/fmt/fmt_test.go
@@ -463,6 +463,15 @@ var fmtTests = []struct {
        {"%#.4x", 1.0, "0x1.0000p+00"},
        {"%#.4g", 1.0, "1.000"},
        {"%#.4g", 100000.0, "1.000e+05"},
+       {"%#.4g", 1.234, "1.234"},
+       {"%#.4g", 0.1234, "0.1234"},
+       {"%#.4g", 1.23, "1.230"},
+       {"%#.4g", 0.123, "0.1230"},
+       {"%#.4g", 1.2, "1.200"},
+       {"%#.4g", 0.12, "0.1200"},
+       {"%#.4g", 10.2, "10.20"},
+       {"%#.4g", 0.0, "0.000"},
+       {"%#.4g", 0.012, "0.01200"},
        {"%#.0f", 123.0, "123."},
        {"%#.0e", 123.0, "1.e+02"},
        {"%#.0x", 123.0, "0x1.p+07"},

diff --git a/src/fmt/format.go b/src/fmt/format.go
index 74e600cab262011d35026edfe492fb2b39206556..4d12f82f7dea84a14d0edd574150115f2c80c64e 100644 (file)
--- a/src/fmt/format.go
+++ b/src/fmt/format.go
@@ -536,6 +536,7 @@ func (f *fmt) fmtFloat(v float64, size int, verb rune, prec int) {
                tail := tailBuf[:0]
 
                hasDecimalPoint := false
+               sawNonzeroDigit := false
                // Starting from i = 1 to skip sign at num[0].
                for i := 1; i < len(num); i++ {
                        switch num[i] {
@@ -552,10 +553,20 @@ func (f *fmt) fmtFloat(v float64, size int, verb rune, prec int) {
                                }
                                fallthrough
                        default:
-                               digits--
+                               if num[i] != '0' {
+                                       sawNonzeroDigit = true
+                               }
+                               // Count significant digits after the first non-zero digit.
+                               if sawNonzeroDigit {
+                                       digits--
+                               }
                        }
                }
                if !hasDecimalPoint {
+                       // Leading digit 0 should contribute once to digits.
+                       if len(num) == 2 && num[1] == '0' {
+                               digits--
+                       }
                        num = append(num, '.')
                }
                for digits > 0 {