internal/impl: simplify extension data structures
The v2 implementation will eagerly unmarshal extension fields,
which means that the logic to synchronize the extensions fields
is no longer necessary. Using type aliases, we can ensure
impl.ExtensionsV1 is identical to the extensions map prior to
a4ab9ec5 from May 2016. This makes it such that we only have one
legacy implementation that we have to deal with.
Change-Id: I41b977e912fbb899c5bc4f055890d474b419429c
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/172240
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/legacy_unknown.go b/internal/impl/legacy_unknown.go
index 759bab9..97eb3be 100644
--- a/internal/impl/legacy_unknown.go
+++ b/internal/impl/legacy_unknown.go
@@ -46,7 +46,7 @@
// and also the extension field map.
type legacyUnknownBytesAndExtensionMap struct {
u pref.UnknownFields
- x legacyExtensionFieldsIface
+ x *legacyExtensionMap
r pref.FieldRanges
}