compatibility.go

// Copyright 2024-2025 Buf Technologies, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package protoplugin

import "sync"

// Protoplugin needs to stay compatible with Go 1.20, as this is the minimum version
// supported by github.com/bufbuild/buf. As such, there are some functions we use
// that are only available in Go 1.21 that we replicate here for now.
//
// When we upgrade to Go 1.20, these should be removed.
//
// License: https://github.com/golang/go/blob/master/LICENSE

// slicesClone returns a copy of the slice.
// The elements are copied using assignment, so this is a shallow clone.
func slicesClone[S ~[]E, E any](s S) S {
	// The s[:0:0] preserves nil in case it matters.
	return append(s[:0:0], s...)
}

// onceValue returns a function that invokes f only once and returns the value
// returned by f. The returned function may be called concurrently.
//
// If f panics, the returned function will panic with the same value on every call.
func onceValue[T any](f func() T) func() T {
	var (
		once   sync.Once
		valid  bool
		p      any
		result T
	)
	g := func() {
		defer func() {
			p = recover()
			if !valid {
				panic(p)
			}
		}()
		result = f()
		f = nil
		valid = true
	}
	return func() T {
		once.Do(g)
		if !valid {
			panic(p)
		}
		return result
	}
}