chore: update changelog and fix lint warnings

- Add all v6 performance optimizations to CHANGELOG.md
- Remove unused nilableType function (unusedfunc warning)
- Remove tautological if-err-nil check in intern.go (nilness warning)

Author: xe-nvdk

CHANGELOG.md

@@ -8,6 +8,15 @@
 - **encode:** `byteSliceWriter` for `Marshal()` path — native `WriteByte` implementation eliminates per-byte heap allocation
 - **encode:** `byteWriter.WriteByte` scratch fix for streaming path — uses `[1]byte` scratch instead of allocating `[]byte{c}`
 - **encode:** `Encode()` fast paths for `map[string]interface{}` and `[]interface{}` — bypasses `reflect.ValueOf` + sync.Map encoder lookup
+- **encode:** `MarshalAppend(dst, v)` API — appends encoded bytes to caller-provided buffer, eliminating the final `make+copy` in `Marshal()` (-26% faster, -94% less memory for callers who reuse buffers)
+- **encode:** two-pass `OmitEmpty` — avoids slice allocation when no fields are omitted (common case for time-series data)
+- **encode:** cache `isZeroer` interface check — pre-computes at struct-discovery time to skip `v.Interface()` boxing during `OmitEmpty` checks
+- **encode/decode:** skip `reflect.Convert` for exact map/slice types — adds `v.Type() == targetType` fast path before `Convert()` for `map[string]string`, `map[string]bool`, `map[string]interface{}`, and `[]string` (-7–8% faster)
+- **encode:** `map[string]string` fast path in `Encode()` type switch — bypasses `reflect.ValueOf` + encoder lookup (-15% faster)
+- **decode:** replace goroutine-per-type `cachedValues` with `sync.Pool` — eliminates goroutine leak and channel synchronization overhead
+- **encode:** pool sorted map key slices via `sync.Pool` — eliminates 1 alloc per sorted map encode for `SetSortMapKeys(true)` callers
+- **decode:** pool recording buffer in `unmarshalValue` — eliminates 1 alloc per `Unmarshaler.UnmarshalMsgpack` call
+- **decode:** inline `hasNilCode` for byte-slice reader path — peeks directly at underlying data, avoiding two interface method calls per nil check (-2–4% faster decode)
 
 ### Bug Fixes
 
@@ -34,6 +43,8 @@
 - Bump `go.mod` to Go 1.26
 - CI: add `-count=1 -timeout=5m` and `GOGC=50` to race tests to prevent OOM on runners ([#33](https://github.com/Basekick-Labs/msgpack/issues/33))
 - CI: change cross-platform step from `go test` to `go vet` (compile-only)
+- Remove tautological `if err != nil` in `decodeInternedInterfaceValue` (nilness warning)
+- Remove unused `nilableType` function from `encode_value.go`
 
 ---
 

encode_value.go

@@ -207,13 +207,6 @@ func nilable(kind reflect.Kind) bool {
 	return false
 }
 
-func nilableType(t reflect.Type) bool {
-	if t.Kind() == reflect.Ptr {
-		t = t.Elem()
-	}
-	return nilable(t.Kind())
-}
-
 //------------------------------------------------------------------------------
 
 func marshalBinaryValueAddr(e *Encoder, v reflect.Value) error {

intern.go

@@ -105,10 +105,8 @@ func decodeInternedInterfaceValue(d *Decoder, v reflect.Value) error {
 		v.Set(reflect.ValueOf(s))
 		return nil
 	}
-	if err != nil {
-		if _, ok := err.(unexpectedCodeError); !ok {
-			return err
-		}
+	if _, ok := err.(unexpectedCodeError); !ok {
+		return err
 	}
 
 	if err := d.s.UnreadByte(); err != nil {