spanner: row.ToStructLenient doesn't work for STRUCT data type

[yfuruyama]

Client

Cloud Spanner

Environment

macOS

Go Environment

$ go version
go version go1.16 darwin/amd64

Code

package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"os"

	"cloud.google.com/go/spanner"
)

type Result struct {
	C []*Inner `spanner:"C"`
}

type Inner struct {
	A int64 `spanner:"A"`
	//B int64 `spanner:"B"`
}

func main() {
	var projectID, instanceID, databaseID string

	flag.StringVar(&projectID, "project", "", "GCP Project ID")
	flag.StringVar(&instanceID, "instance", "", "Cloud Spanner Instance ID")
	flag.StringVar(&databaseID, "database", "", "Cloud Spanner Database ID")
	flag.Parse()

	if projectID == "" || instanceID == "" || databaseID == "" {
		flag.Usage()
		os.Exit(1)
	}

	dbPath := fmt.Sprintf("projects/%s/instances/%s/databases/%s", projectID, instanceID, databaseID)
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, dbPath)
	if err != nil {
		log.Fatalf("failed to create spanner client: %v", err)
	}
	defer client.Close()

	query := "SELECT ARRAY(SELECT STRUCT(1 AS A, 2 AS B)) AS C"
	if err := client.Single().Query(ctx, spanner.NewStatement(query)).Do(func(r *spanner.Row) error {
		var result Result
		return r.ToStructLenient(&result)
	}); err != nil {
		log.Fatalf("failed to run query: %v", err)
	}
}

Expected behavior

row.ToStructLenient should decode the row successfully.

Actual behavior

Got the following decoding error.

2022/04/25 23:45:10 failed to run query: spanner: code = "InvalidArgument", desc = "cannot decode field C of Cloud Spanner STRUCT fields:{name:\"C\" type:{code:ARRAY array_element_type:{code:STRUCT struct_type:{fields:{name:\"A\" type:{code:INT64}} fields:{name:\"B\" type:{code:INT64}}}}}}, cannot decode list_value:{values:{string_value:\"1\"} values:{string_value:\"2\"}}(array element 0) as STRUCT, Go struct &{A:1}(type *main.Inner) has no or duplicate fields for Cloud Spanner STRUCT field B"
exit status 1

Screenshots

N/A

Additional context

• STRUCT type is used in Spanner system table as well (e.g. SAMPLE_LOCK_REQUESTS in lock-statistics), so it's preferable to allow users to use row.ToStructLenient to decode inner STRUCT type.

[rahul2393]

Thanks @yfuruyama for opening the issue, I have created the PR to address this, please take a look.