cmd/go: invoking go run from go test can corrupt build cache

[rittneje]

Go version

go version go1.22.7 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/tmp/.gocache'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.7'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/Users/rittneje/go-test-bug/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-build1468831127=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I have the following files:

go.mod

module gotestbug

go 1.22

pkg1/foo_test.go

package pkg1

import (
	"bytes"
	"os/exec"
	"path/filepath"
	"testing"
)

func TestFoo(t *testing.T) {
	cmd := exec.Command("go", "run", filepath.Join("testdata", "main.go"))
	output := new(bytes.Buffer)
	cmd.Stdout = output
	cmd.Stderr = output

	t.Logf("+ %s", cmd)
	if err := cmd.Run(); err != nil {
		t.Fatal(err, output)
	}
}

pkg1/testdata/main.go

package main

func main() {
}

pkg2/bar_test.go

package pkg2

import (
	"testing"
)

func TestBar(t *testing.T) {
	t.Log("hello")
}

I then ran the following commands as root to prime the build cache. (I intentionally set the mtimes and trim.txt file to the past in order to reproduce the bug.)

go clean -cache
go build std
chmod -R a+rwX "${GOCACHE}"
find "${GOCACHE}" -type f -exec touch '{}' -d '2024-07-01 00:00:00' \;
printf '1719792000' > "${GOCACHE}/trim.txt"

Finally I ran go test as a non-root user. (I passed -p=1 to force it to run one package at a time in order to make the bug happen deterministically.)

go test -v -count=1 -p=1 ./...

What did you see happen?

As described in #69565, since the build cache was crafted to look old, go run decided to trim it. This somehow causes go test to break.

=== RUN   TestFoo
    foo_test.go:16: + /usr/local/go/bin/go run testdata/main.go
--- PASS: TestFoo (0.15s)
PASS
ok      gotestbug/pkg1  0.148s
# gotestbug/pkg2 [gotestbug/pkg2.test]
pkg2/bar_test.go:4:2: could not import testing (open /tmp/.gocache/26/26737db8c74b26401dc8828801cc3793a888d7c29c40b7500b7e9e5f96deec19-d: no such file or directory)
FAIL    gotestbug/pkg2 [build failed]
FAIL

It should be noted that this issue does not happen if I run go test as root.

What did you expect to see?

The test should pass without any compilation issues.

[gabyhelp]

Related Issues and Documentation

• cmd/go: go build errors that don't correspond to source file until build cache is cleared #69179
• build: run.bash: make test configuration independent of the user's GOENV file #54084 (closed)
• cmd/go: error if GOCACHE is set but is not an absolute path #30447 (closed)
• cmd/go: tests fail when GOROOT is stale #48698 (closed)
• cmd/go: test reported as cached, but not actually cached #41593
• cmd/go clean -testcache does not clean test cache #29757 (closed)
• go/build: tests use a non-hermetic "go" binary #39198 (closed)
• cmd/go: cache not invalidated if testdata files are changed while the test is running #26790
• x/tools/gopls/test/debug: test fails when run in the module cache #59841 (closed)
• cmd/go: 'go test' fails to cache test result due to modified `.git` directory #52573 (closed)

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[dr2chase]

@adonovan , @neild , @rsc

[rittneje]

@adonovan , @neild , @rsc following up on this