fmt: restore padding for %x on byte slices and strings
Also improve the documentation. A prior fix in this release
changed the properties for empty strings and slices, incorrectly.
Previous behavior is now restored and better documented.
Add lots of tests.
The behavior is that when using a string-like format (%s %q %x %X)
a byte slice is equivalent to a string, and printed as a unit. The padding
applies to the entire object. (The space and sharp flags apply
elementwise.)
Fixes #11422.
Fixes #10430.
Change-Id: I758f0521caf71630437e43990ec6d6c9a92655e3
Reviewed-on: https://go-review.googlesource.com/11600
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/src/fmt/doc.go b/src/fmt/doc.go
index 2efe6ee..ef91368 100644
--- a/src/fmt/doc.go
+++ b/src/fmt/doc.go
@@ -40,7 +40,7 @@
%F synonym for %f
%g %e for large exponents, %f otherwise
%G %E for large exponents, %F otherwise
- String and slice of bytes:
+ String and slice of bytes (treated equivalently with these verbs):
%s the uninterpreted bytes of the string or slice
%q a double-quoted string safely escaped with Go syntax
%x base 16, lower-case, two characters per byte
@@ -164,6 +164,9 @@
of strings, and %6.2f will control formatting for each element
of a floating-point array.
+ However, when printing a byte slice with a string-like verb
+ (%s %q %x %X), it is treated identically to a string, as a single item.
+
To avoid recursion in cases such as
type X string
func (x X) String() string { return Sprintf("<%s>", x) }
diff --git a/src/fmt/fmt_test.go b/src/fmt/fmt_test.go
index 28b7e05..90a4031 100644
--- a/src/fmt/fmt_test.go
+++ b/src/fmt/fmt_test.go
@@ -452,10 +452,30 @@
{"%q", []string{"a", "b"}, `["a" "b"]`},
{"% 02x", []byte{1}, "01"},
{"% 02x", []byte{1, 2, 3}, "01 02 03"},
- // Special care for empty slices.
+ // Padding with byte slices.
{"%x", []byte{}, ""},
- {"%02x", []byte{}, ""},
- {"% 02x", []byte{}, ""},
+ {"%02x", []byte{}, "00"},
+ {"% 02x", []byte{}, "00"},
+ {"%08x", []byte{0xab}, "000000ab"},
+ {"% 08x", []byte{0xab}, "000000ab"},
+ {"%08x", []byte{0xab, 0xcd}, "0000abcd"},
+ {"% 08x", []byte{0xab, 0xcd}, "000ab cd"},
+ {"%8x", []byte{0xab}, " ab"},
+ {"% 8x", []byte{0xab}, " ab"},
+ {"%8x", []byte{0xab, 0xcd}, " abcd"},
+ {"% 8x", []byte{0xab, 0xcd}, " ab cd"},
+ // Same for strings
+ {"%x", "", ""},
+ {"%02x", "", "00"},
+ {"% 02x", "", "00"},
+ {"%08x", "\xab", "000000ab"},
+ {"% 08x", "\xab", "000000ab"},
+ {"%08x", "\xab\xcd", "0000abcd"},
+ {"% 08x", "\xab\xcd", "000ab cd"},
+ {"%8x", "\xab", " ab"},
+ {"% 8x", "\xab", " ab"},
+ {"%8x", "\xab\xcd", " abcd"},
+ {"% 8x", "\xab\xcd", " ab cd"},
// renamings
{"%v", renamedBool(true), "true"},
diff --git a/src/fmt/format.go b/src/fmt/format.go
index ac9f6d8..517b18f 100644
--- a/src/fmt/format.go
+++ b/src/fmt/format.go
@@ -346,7 +346,7 @@
}
buf = append(buf, digits[c>>4], digits[c&0xF])
}
- f.buf.Write(buf)
+ f.pad(buf)
}
// fmt_sx formats a string as a hexadecimal encoding of its bytes.
