spanner: ToStruct does not decode if target field is a pointer to a named type #12576
Description
Client
Spanner
Environment
go version go1.24.4 linux/amd64
Code and Dependencies
package main
import (
"context"
"fmt"
"log"
"os"
"cloud.google.com/go/spanner"
)
type CustomString string
type MyBigStruct struct {
ExampleId string
ExampleString *CustomString
}
func main() {
if len(os.Args) < 3 {
log.Fatal("Usage: spanner-bug project-id instance database")
}
project := os.Args[1]
instance := os.Args[2]
database := os.Args[3]
dsn := fmt.Sprintf("projects/%s/instances/%s/databases/%s", project, instance, database)
ctx := context.Background()
spannerClient, err := spanner.NewClient(ctx, dsn)
if err != nil {
log.Fatalf("Failed to create client %v", err)
}
_, err = spannerClient.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
stmt := spanner.NewStatement(`INSERT ExampleTable (ExampleId, ExampleString) VALUES (@ExampleId, @ExampleString)`)
stmt.Params["ExampleId"] = "id-123"
stmt.Params["ExampleString"] = "foobar"
_, err = txn.Update(ctx, stmt)
return err
})
if err != nil {
log.Fatalf("Failed to insert data: %v", err)
}
stmt := spanner.NewStatement(`SELECT ExampleId, ExampleString FROM ExampleTable where ExampleId = @exampleId LIMIT 1`)
stmt.Params["ExampleId"] = "id-123"
iter := spannerClient.Single().Query(ctx, stmt)
row, err := iter.Next()
if err != nil {
log.Fatalf("failed to get example row from iterator: %v", err)
}
var e MyBigStruct
err = row.ToStruct(&e)
if err != nil {
log.Fatalf("failed to call ToStruct on example row: %v", err)
}
}go.mod
module spannerbuggo 1.24.4
require cloud.google.com/go/spanner v1.83.0
require (
cel.dev/expr v0.23.0 // indirect
cloud.google.com/go v0.121.2 // indirect
cloud.google.com/go/auth v0.16.2 // indirect
cloud.google.com/go/auth/oauth2adapt v0.2.8 // indirect
cloud.google.com/go/compute/metadata v0.7.0 // indirect
cloud.google.com/go/monitoring v1.24.2 // indirect
github.com/GoogleCloudPlatform/grpc-gcp-go/grpcgcp v1.5.3 // indirect
github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.27.0 // indirect
github.com/cespare/xxhash/v2 v2.3.0 // indirect
github.com/cncf/xds/go v0.0.0-20250326154945-ae57f3c0d45f // indirect
github.com/envoyproxy/go-control-plane/envoy v1.32.4 // indirect
github.com/envoyproxy/protoc-gen-validate v1.2.1 // indirect
github.com/felixge/httpsnoop v1.0.4 // indirect
github.com/go-jose/go-jose/v4 v4.0.5 // indirect
github.com/go-logr/logr v1.4.2 // indirect
github.com/go-logr/stdr v1.2.2 // indirect
github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
github.com/google/s2a-go v0.1.9 // indirect
github.com/google/uuid v1.6.0 // indirect
github.com/googleapis/enterprise-certificate-proxy v0.3.6 // indirect
github.com/googleapis/gax-go/v2 v2.14.2 // indirect
github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
github.com/spiffe/go-spiffe/v2 v2.5.0 // indirect
github.com/zeebo/errs v1.4.0 // indirect
go.opencensus.io v0.24.0 // indirect
go.opentelemetry.io/auto/sdk v1.1.0 // indirect
go.opentelemetry.io/contrib/detectors/gcp v1.36.0 // indirect
go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.61.0 // indirect
go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.61.0 // indirect
go.opentelemetry.io/otel v1.36.0 // indirect
go.opentelemetry.io/otel/metric v1.36.0 // indirect
go.opentelemetry.io/otel/sdk v1.36.0 // indirect
go.opentelemetry.io/otel/sdk/metric v1.36.0 // indirect
go.opentelemetry.io/otel/trace v1.36.0 // indirect
golang.org/x/crypto v0.39.0 // indirect
golang.org/x/net v0.41.0 // indirect
golang.org/x/oauth2 v0.30.0 // indirect
golang.org/x/sync v0.15.0 // indirect
golang.org/x/sys v0.33.0 // indirect
golang.org/x/text v0.26.0 // indirect
golang.org/x/time v0.12.0 // indirect
google.golang.org/api v0.237.0 // indirect
google.golang.org/genproto v0.0.0-20250505200425-f936aa4a68b2 // indirect
google.golang.org/genproto/googleapis/api v0.0.0-20250603155806-513f23925822 // indirect
google.golang.org/genproto/googleapis/rpc v0.0.0-20250603155806-513f23925822 // indirect
google.golang.org/grpc v1.73.0 // indirect
google.golang.org/protobuf v1.36.6 // indirect
)
module modname
go 1.24.0
require (
// ...
)
Expected behavior
.ToStruct or .ToStructLenient is able to decode a string into a pointer to a custom string type.
Actual behavior
Both .ToStruct and .ToStructLenient return an error when trying to decode a string into a pointer to a custom string type:
spanner: code = "InvalidArgument", desc = "cannot decode field ExampleString of Cloud Spanner STRUCT fields:{name:\"ExampleId\" type:{code:STRING}} fields:{name:\"ExampleString\" type:{code:STRING}}, type **main.CustomString cannot be used for decoding STRING"
Additional context
This looks like it's unhandled but expected behavior based off the comments and logic in spanner/value.go's getDecodableSpannerType() and decodeValueToCustomType().