database/sql: fallback to default argument conversion fails when ColumnConverter is implemented

[flimzy]

Go version

go version go1.22.0 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/jonhall/.cache/go-build'
GOENV='/home/jonhall/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/jonhall/go/pkg/mod'
GONOPROXY='gitlab.com/FlashbackSRS/priv,gitlab.com/flimzy/hacker-portfolio'
GONOSUMDB='gitlab.com/FlashbackSRS/priv,gitlab.com/flimzy/hacker-portfolio'
GOOS='linux'
GOPATH='/home/jonhall/go'
GOPRIVATE='gitlab.com/FlashbackSRS/priv,gitlab.com/flimzy/hacker-portfolio'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='/usr/bin/gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/jonhall/src/bugrepro/go.mod'
GOWORK=''
CGO_CFLAGS='-w'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1095939242=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I wrote a database/sql driver that implements the optional ColumnConverter interface for prepared statements, and for which NumInputs() returns -1.

Technically, I wrote a databse/sql proxy driver, for the purpose of adding hooks to DB operations, to aide in debugging. See https://gitlab.com/flimzy/errsql

But using this library with modernc.org/sqlite is what triggered the buggy behavior. modernc.org/sqlite itself does not implement the ColumnConverter interface, but it does return -1 for NumInputs. Because the proxy driver does implement ColumnConverter (because it must implement it for all drivers it proxies, or none), it triggers the observed behavior.

What did you see happen?

The default argument conversion is never called, leading to errors about invalid driver.Value values.

What did you expect to see?

I expected that the default argument conversion would happen.