Golang cmd/go: test -cover can't find covdata tool with switched toolchain and empty tests

Go version

go version go1.25.0 linux/amd64

Output of `go env` in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/mauclair/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/mauclair/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/home/mauclair/tmp/go-build2752909789=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/mauclair/go/src/github.com/mikeauclair/toolchain_covdata_replicate/go.mod'
GOMODCACHE='/home/mauclair/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/mauclair/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/mauclair/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.0.linux-amd64'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/mauclair/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/mauclair/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.0.linux-amd64/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.25.0'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Ran go test -cover on a package with no test files (with a go 1.25 toolchain downloaded automatically)

What did you see happen?

# github.com/mikeauclair/toolchain_covdata_replicate
go: no such tool "covdata"

What did you expect to see?

        github.com/mikeauclair/toolchain_covdata_replicate              %

Comment From: mikeauclair

I pushed up a quick replication case here https://github.com/mikeauclair/toolchain_covdata_replicate, showing that this works with a system-installed version of go and only seems to fail with the auto-downloaded toolchain

Comment From: trym-moeller

It can be noted that manually running go env -w GOTOOLCHAIN=go1.25.0+auto fixed a similar problem for me.

Comment From: jerbob92