feature: use parent source location path if the original one is missing

[maratori]

If I provide a valid source location path to check.WithFileNameAndSourcePath, but it's missing from the file, the annotation points to the file. I would expect the nearest parent to be found for the annotation.

Usually, the path should always exist. However, working with options, this may be the case. For example, the following file contains a path pointing to (x).y but missing a path to (x). In this case, an annotation for message options should be created.

extend google.protobuf.MessageOptions {
  X x = 5000;
}
message X {
  string y = 1;
}
message Foo {
  option (x).y = "z";
}

Go test to reproduce the issue

package x_test

import (
	"context"
	"os"
	"path/filepath"
	"testing"

	"github.com/stretchr/testify/require"

	"buf.build/go/bufplugin/check"
	"buf.build/go/bufplugin/check/checktest"
	"buf.build/go/bufplugin/check/checkutil"
	"buf.build/go/bufplugin/descriptor"
)

const protoFile = `
syntax = "proto3";
import "google/protobuf/descriptor.proto";
extend google.protobuf.MessageOptions {
  X x = 5000;
}
message X {
  string y = 1;
}
message Foo {
  option (x).y = "z";
}
`

func TestX(t *testing.T) {
	dir := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(dir, "file.proto"), []byte(protoFile), 0666))
	checktest.CheckTest{
		Request: &checktest.RequestSpec{
			Files: &checktest.ProtoFileSpec{
				DirPaths:  []string{dir},
				FilePaths: []string{"file.proto"},
			},
			RuleIDs: []string{"XXX"},
		},
		Spec: &check.Spec{
			Rules: []*check.RuleSpec{{
				ID:      "XXX",
				Purpose: "X.",
				Type:    check.RuleTypeLint,
				Handler: checkutil.NewFileRuleHandler(
					func(
						_ context.Context,
						writer check.ResponseWriter,
						_ check.Request,
						file descriptor.FileDescriptor,
					) error {
						foo := file.ProtoreflectFileDescriptor().Messages().ByName("Foo")
						writer.AddAnnotation(
							check.WithMessage("X"),
							check.WithFileNameAndSourcePath(
								"file.proto",
								append(
									file.ProtoreflectFileDescriptor().SourceLocations().ByDescriptor(foo).Path,
									7,
									5000,
								),
							),
						)
						return nil
					},
					checkutil.WithoutImports(),
				),
			}},
		},
		ExpectedAnnotations: []checktest.ExpectedAnnotation{{
			RuleID:  "XXX",
			Message: "X",
			FileLocation: &checktest.ExpectedFileLocation{
				FileName:    "file.proto",
				StartLine:   10,
				StartColumn: 2,
				EndLine:     10,
				EndColumn:   21,
			},
		}},
	}.Run(t)
}