cmd/go: bad error message when using vendor directory while specifying too old Go version

[dominikh]

Go version

go version devel go1.23-722d59436b Thu May 16 02:00:26 2024 +0000 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/dominikh/.cache/go-build'
GOENV='/home/dominikh/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/dominikh/prj/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/dominikh/prj'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/dominikh/prj/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/dominikh/prj/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='devel go1.23-722d59436b Thu May 16 02:00:26 2024 +0000'
GODEBUG=''
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/tmp/foo/go.mod'
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 -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3571202171=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Run go build in

-- foo.go --
package foo

import _ "github.com/foo/bar"
-- go.mod --
module example.com

go 1.13
-- vendor/github.com/foo/bar/bar.go --
package bar

What did you see happen?

foo.go:3:8: cannot find module providing package github.com/foo/bar: import lookup disabled by -mod=readonly
	(Go version in go.mod is unspecified, so vendor directory was not used.)

What did you expect to see?

I did not expect to see Go version in go.mod is unspecified since a version is specified, it's just too old (older than 1.14) for Go to default to -mod=vendor

[gopherbot]

Change https://go.dev/cl/588075 mentions this issue: cmd/go/internal/modload: fix bug in error message