bazel coverage panics if flag.CommandLine is reassigned #4383
Description
When run with go test -cover, the following test does not panic:
-- foo.go --
package foo
func foo() int {
return 42
}
-- foo_test.go --
package foo
import (
"flag"
"testing"
)
func TestReassign(t *testing.T) {
flag.CommandLine = flag.NewFlagSet("test", flag.ExitOnError)
_ = foo()
}
However, with bazel coverage, it does panic:
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x20 pc=0x100f8dbe4]
goroutine 1 [running]:
github.com/bazelbuild/rules_go/go/tools/bzltestutil.ConvertCoverToLcov()
external/io_bazel_rules_go/go/tools/bzltestutil/lcov.go:39 +0x54
github.com/bazelbuild/rules_go/go/tools/bzltestutil.lcovAtExitHook()
external/io_bazel_rules_go/go/tools/bzltestutil/lcov.go:181 +0x1c
github.com/bazelbuild/rules_go/go/tools/bzltestutil.LcovTestDeps.SetPanicOnExit0({{}, 0x18?}, 0x4b?)
external/io_bazel_rules_go/go/tools/bzltestutil/lcov.go:175 +0x24
testing.(*M).after(0x1400007c280?)
GOROOT/src/testing/testing.go:2374 +0x74
testing.(*M).Run(0x1400007c280)
GOROOT/src/testing/testing.go:2185 +0x940
main.main()
bazel-out/darwin_arm64-fastbuild/bin/go_default_test_/testmain.go:157 +0x7a4
The cause is that the test reassigned flag.CommandLine
and did not restore the original value.
While that's bad behavior, go test does not explode,
so neither should bazel coverage.