types/views: add MarshalJSONV2 to Slicebradfitz/json2

It helps, but not all the way.

                               │   before   │                  after                  │
                               │    B/op    │    B/op      vs base                    │
    JSONMarshalView/v1_slice-8   64.00 ± 0%   64.00 ± ∞ ¹        ~ (p=1.000 n=10+1) ²
    JSONMarshalView/v1_view-8    136.0 ± 0%   136.0 ± ∞ ¹        ~ (p=1.000 n=10+1) ²
    JSONMarshalView/v2_slice-8   64.00 ± 0%   64.00 ± ∞ ¹        ~ (p=1.000 n=10+1) ²
    JSONMarshalView/v2_view-8    136.0 ± 0%   112.0 ± ∞ ¹  -17.65% (n=10+1)

Updates tailscale/corp#14379
Updates tailscale/corp#21429 (new benchmark)

Change-Id: I891dd6a4db1a995ae1be14f8c5085629bb30b8da
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/types/views/views.go b/types/views/views.go
index 42758966f..fa0e45adb 100644
--- a/types/views/views.go
+++ b/types/views/views.go
@@ -13,6 +13,9 @@ import (
 	"maps"
 	"slices"
 
+	jsonexp "github.com/go-json-experiment/json"
+	jsontext "github.com/go-json-experiment/json/jsontext"
+
 	"go4.org/mem"
 )
 
@@ -225,6 +228,13 @@ func (v Slice[T]) MarshalJSON() ([]byte, error) {
 	return json.Marshal(v.ж)
 }
 
+var _ jsonexp.MarshalerV2 = Slice[string]{nil}
+
+// MarshalJSON implements github.com/go-json-experiment/json.MarshalerV2.
+func (v Slice[T]) MarshalJSONV2(e *jsontext.Encoder, opts jsonexp.Options) error {
+	return jsonexp.MarshalEncode(e, v.ж, opts)
+}
+
 // UnmarshalJSON implements json.Unmarshaler.
 func (v *Slice[T]) UnmarshalJSON(b []byte) error {
 	return unmarshalSliceFromJSON(b, &v.ж)