internal/protodetecttypes/protodetecttypes.go

// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package protodetecttypes identifies static types (go/types, typically
// obtained at build time) generated by protoc-gen-go. The protodetectreflect
// package is the counterpart for dynamic types (reflect, obtained at runtime).
package protodetecttypes

import (
	"go/types"
	"reflect"
	"strings"
)

// Type represents a go/types.Type obtained at build time.
type Type struct{ T types.Type }

// IsMessage reports whether t is a generated message.
func (t Type) IsMessage() bool {
	return t.MessageAPI() != Invalid
}

// MessageAPI determines the API of the generated message.
func (t Type) MessageAPI() MessageAPI {
	if t, ok := t.T.Underlying().(*types.Struct); ok && t.NumFields() > 0 {
		return determineAPI(reflect.StructTag(t.Tag(0)))
	}
	return Invalid
}

// MessageAPI determines which API is used for the generated message type.
type MessageAPI int

const (
	// Invalid indicates the specified type is not a proto message.
	Invalid MessageAPI = iota

	// OpenAPI indicates a message generated in the open struct API,
	// where the message representation is a Go struct with exported fields.
	OpenAPI

	// HybridAPI indicates a message generated in the hybrid API,
	// where the message has properties of both OpenAPI and OpaqueAPI.
	HybridAPI

	// OpaqueAPI indicates a message generated in the opaque API,
	// where the message can only be interacted with through accessor methods.
	OpaqueAPI
)

// DetermineAPI determines the message API from a magic struct tag that
// protoc-gen-go emits for all messages.
func determineAPI(tag reflect.StructTag) MessageAPI {
	switch s := tag.Get("protogen"); {
	case strings.HasPrefix(s, "open."):
		return OpenAPI
	case strings.HasPrefix(s, "hybrid."):
		return HybridAPI
	case strings.HasPrefix(s, "opaque."):
		return OpaqueAPI
	default:
		return Invalid
	}
}