fmt: don't pad strings with zeros

It's what the documentation says, and oddly it already behaves correctly
for right padding, not left. (We never pad with zeros on the right.)

Just don't do it.

Fixes #56486

Change-Id: I2465edea93c69084e33bee0d945d5a1b85e6cd14
Reviewed-on: https://go-review.googlesource.com/c/go/+/555776
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Rob Pike <r@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

diff --git a/src/fmt/fmt_test.go b/src/fmt/fmt_test.go
index 6a79862f285f331545becb8fe015bbbd06ae80c9..3f82fb681445b719c1f0a1918e652396ab98a5e1 100644 (file)
--- a/src/fmt/fmt_test.go
+++ b/src/fmt/fmt_test.go
@@ -304,8 +304,8 @@ var fmtTests = []struct {
        {"%2s", []byte("\u263a"), " ☺"},
        {"%-5s", "abc", "abc  "},
        {"%-5s", []byte("abc"), "abc  "},
-       {"%05s", "abc", "00abc"},
-       {"%05s", []byte("abc"), "00abc"},
+       {"%05s", "abc", "  abc"},
+       {"%05s", []byte("abc"), "  abc"},
        {"%5s", "abcdefghijklmnopqrstuvwxyz", "abcdefghijklmnopqrstuvwxyz"},
        {"%5s", []byte("abcdefghijklmnopqrstuvwxyz"), "abcdefghijklmnopqrstuvwxyz"},
        {"%.5s", "abcdefghijklmnopqrstuvwxyz", "abcde"},

diff --git a/src/fmt/print.go b/src/fmt/print.go
index cb393bd76370daa72b9af3bb8cdd2394787451bc..9596888854763af74e533abbfb187906c887d91b 100644 (file)
--- a/src/fmt/print.go
+++ b/src/fmt/print.go
@@ -703,6 +703,11 @@ func (p *pp) printArg(arg any, verb rune) {
                return
        }
 
+       // Bug fix: avoid padding strings with zeros. Issue 56486.
+       if verb == 's' {
+               p.fmt.zero = false
+       }
+
        // Some types can be done without reflection.
        switch f := arg.(type) {
        case bool: