database/sql: use %w verb for valuer errors to enable errors.Is/As

[joshgarrett-hellofresh]

Go version

go version go1.21.4 darwin/arm64

What operating system and processor architecture are you using (go env)?

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/gofer/Library/Caches/go-build'
GOENV='/Users/gofer/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/gofer/go/pkg/mod'
GOOS='darwin'
GOPATH='/Users/gofer/go'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.21.4/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.21.4/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.4'
GCCGO='gccgo'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/cf/314tnd5d22129h1z7srmcklr0000gn/T/go-build479648600=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

package main

import (
	"context"
	"database/sql"
	"database/sql/driver"
	"errors"
)

type Valuer struct {
	field []byte
}

func (v Valuer) Value() (driver.Value, error) {
	if len(v.field) == 0 {
		// return an error that we hope to be able to handle later
		return nil, errEmpty
	}
	return v, nil
}

// errEmpty is returned when an empty value is found
var errEmpty = errors.New("empty value")

func main() {
	db, _ := sql.Open("pgx", dsn)
	_, err := db.ExecContext(
		context.Background(),
		`INSERT INTO some_table (some_bytea_column) VALUES ($1)`,
		&Valuer{nil},
	)
	// errors.Is doesn't work b/c %v verb was used for error instead of %w
	if !errors.Is(err, errEmpty) {
		panic(err)
	}
}

What did you expect to see?

errors.Is should be able to detect sentinel errors returned by valuer. error will need to be properly wrapped by fmt.Errorf with %w verb instead of %v, similar to scanner

What did you see instead?

valuer errors are wrapped by fmt.Errorf with %v verb

[mauri870]

Edited your issue to add a code block.

[mauri870]

I don't think this can cause any issues, so feel free to send a CL. Thanks!

[gopherbot]

Change https://go.dev/cl/550116 mentions this issue: database/sql: wrap errors with %w in driverArgsConnLocked

[callthingsoff]

Related issue #44635, and CL https://go-review.googlesource.com/c/go/+/333990

[aimuz]

@mauri870 Can you help me review CL? https://go.dev/cl/550116

[gopherbot]

Change https://go.dev/cl/568755 mentions this issue: doc/go1.23: document database/sql wrap errors