encoding/json/jsontext: preserve buffer capacity in Encoder.Reset

This does the equivalent of CL 681177 for the Encoder.
It preserves the internal buffer between resets.

Change-Id: I5e9353b6d7755e067d4f9a4d1ea3d8f056253027
Reviewed-on: https://go-review.googlesource.com/c/go/+/690375
Reviewed-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 2 insertions, 4 deletions

diff --git a/src/encoding/json/jsontext/decode.go b/src/encoding/json/jsontext/decode.go
index b9f247bff4..f505de4468 100644
--- a/src/encoding/json/jsontext/decode.go
+++ b/src/encoding/json/jsontext/decode.go
@@ -138,12 +138,10 @@ func (d *Decoder) Reset(r io.Reader, opts ...Options) {
 	case d.s.Flags.Get(jsonflags.WithinArshalCall):
 		panic("jsontext: cannot reset Decoder passed to json.UnmarshalerFrom")
 	}
-	// If the decoder was previously aliasing a bytes.Buffer,
-	// invalidate the alias to avoid writing into the bytes.Buffer's
-	// internal buffer.
+	// Reuse the buffer if it does not alias a previous [bytes.Buffer].
 	b := d.s.buf[:0]
 	if _, ok := d.s.rd.(*bytes.Buffer); ok {
-		b = nil // avoid reusing b since it aliases the previous bytes.Buffer.
+		b = nil
 	}
 	d.s.reset(b, r, opts...)
 }