cmd/go: import of vendored package error "cannot find package" from testdata package

[prattmic]

What version of Go are you using (go version)?

$ go version
go version devel go1.18-f6d4b9ad5c Mon Dec 13 16:39:15 2021 -0500 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/usr/local/google/home/mpratt/.cache/go-build"
GOENV="/usr/local/google/home/mpratt/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/usr/local/google/home/mpratt/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/usr/local/google/home/mpratt/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/google/home/mpratt/src/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/google/home/mpratt/src/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="devel go1.18-f6d4b9ad5c Mon Dec 13 16:39:15 2021 -0500"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/usr/local/google/home/mpratt/src/go/src/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build1377042719=/tmp/go-build -gno-record-gcc-switches"

What did you do?

1. Checkout https://golang.org/cl/371298
2. Build: ./bin/go build cmd/testdata/foo

What did you expect to see?

Successful build

What did you see instead?

cmd/testdata/foo/main.go:4:2: cannot find package

Note that the binary in cmd/foo builds just fine. The only difference is that the former is in a testdata/ directory. golang.org/x/sys/unix is vendored in cmd/vendor/....

cc @bcmills

[bcmills]

Funky. I modified cmd/go/internal/modload.(*loader).stdVendor to log the return vendorPath exits, and it is resolving these imports to the correct paths. I'm not sure where they're being lost. 🤔

[bcmills]

Oddly, though, the module loader sees the package as inStd but go list -e -f {{.Standard}} reports false.

[gopherbot]

Change https://golang.org/cl/371298 mentions this issue: DO NOT SUBMIT: testdata vendoring bug