Generic slice unmarshal fn

internal/danger/slices_optimized.go

@@ -0,0 +1,30 @@
+//go:build !go1.18
+// +build !go1.18
+
+package danger
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+//go:linkname unsafe_NewArray reflect.unsafe_NewArray
+func unsafe_NewArray(rtype unsafe.Pointer, length int) unsafe.Pointer
+
+//go:linkname typedslicecopy reflect.typedslicecopy
+//go:noescape
+func typedslicecopy(elemType unsafe.Pointer, dst, src Slice) int
+
+func ExtendSlice(t reflect.Type, s *Slice, n int) Slice {
+	elemTypeRef := t.Elem()
+	elemTypePtr := ((*iface)(unsafe.Pointer(&elemTypeRef))).ptr
+
+	d := Slice{
+		Data: unsafe_NewArray(elemTypePtr, n),
+		Len:  s.Len,
+		Cap:  n,
+	}
+
+	typedslicecopy(elemTypePtr, d, *s)
+	return d
+}