Initial QSfera import

Server/vendor/go.opentelemetry.io/otel/attribute/internal/attribute.go

@@ -0,0 +1,75 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+/*
+Package attribute provide several helper functions for some commonly used
+logic of processing attributes.
+*/
+package attribute // import "go.opentelemetry.io/otel/attribute/internal"
+
+import (
+	"reflect"
+)
+
+// sliceElem is the exact set of element types stored in attribute slice values.
+// Using a closed set prevents accidental instantiations for unsupported types.
+type sliceElem interface {
+	bool | int64 | float64 | string
+}
+
+// SliceValue converts a slice into an array with the same elements.
+func SliceValue[T sliceElem](v []T) any {
+	// Keep only the common tiny-slice cases out of reflection. Extending this
+	// much further increases code size for diminishing benefit while larger
+	// slices still need the generic reflective path to preserve comparability.
+	// This matches the short lengths that show up most often in local
+	// benchmarks and semantic convention examples while leaving larger, less
+	// predictable slices on the generic reflective path.
+	switch len(v) {
+	case 0:
+		return [0]T{}
+	case 1:
+		return [1]T{v[0]}
+	case 2:
+		return [2]T{v[0], v[1]}
+	case 3:
+		return [3]T{v[0], v[1], v[2]}
+	}
+
+	return sliceValueReflect(v)
+}
+
+// AsSlice converts an array into a slice with the same elements.
+func AsSlice[T sliceElem](v any) []T {
+	// Mirror the small fixed-array fast path used by SliceValue.
+	switch a := v.(type) {
+	case [0]T:
+		return []T{}
+	case [1]T:
+		return []T{a[0]}
+	case [2]T:
+		return []T{a[0], a[1]}
+	case [3]T:
+		return []T{a[0], a[1], a[2]}
+	}
+
+	return asSliceReflect[T](v)
+}
+
+func sliceValueReflect[T sliceElem](v []T) any {
+	cp := reflect.New(reflect.ArrayOf(len(v), reflect.TypeFor[T]())).Elem()
+	reflect.Copy(cp, reflect.ValueOf(v))
+	return cp.Interface()
+}
+
+func asSliceReflect[T sliceElem](v any) []T {
+	rv := reflect.ValueOf(v)
+	if !rv.IsValid() || rv.Kind() != reflect.Array || rv.Type().Elem() != reflect.TypeFor[T]() {
+		return nil
+	}
+	cpy := make([]T, rv.Len())
+	if len(cpy) > 0 {
+		_ = reflect.Copy(reflect.ValueOf(cpy), rv)
+	}
+	return cpy
+}