panic: runtime error: SIGSEGV when permission denied on log file

[oernii]

Describe the bug
App crashes when zap tries to create a logfile in a directory where there user has no permission to write

To Reproduce

• have non-root user
• start app in / for example or any non-writable dir
• crash:

 panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x6b95ca]

goroutine 1 [running]:
go.uber.org/zap.(*Logger).check(0x0, 0x0, {0x74735b, 0x17})
        /root/go/pkg/mod/go.uber.org/zap@v1.23.0/logger.go:291 +0x6a
go.uber.org/zap.(*Logger).Info(0xc0000186b8?, {0x74735b?, 0x0?}, {0x0, 0x0, 0x0})
        /root/go/pkg/mod/go.uber.org/zap@v1.23.0/logger.go:212 +0x3b
main.main()
        /builds/build/app/main.go:30 +0x1a5

Expected behavior
Zap should crash with an "permission denied" error, not SEGV

Additional context
Similar to #390

[JacobOaks]

Hey, thanks for reporting this.

How are you building your logger? The crash is indicating to me that the logger itself is nil. I was able to reproduce this by creating a logger from a config with a sink to a file in / but all I had to do to avoid the nil dereference was check for an error from Config.Build():

func main() {
    conf := zap.NewProductionConfig()
    conf.OutputPaths = append(conf.OutputPaths, "/output.log")
    logger, err := conf.Build()
    if err != nil {
        fmt.Printf("err creating logger: %v\n", err)
        return
    }
    defer logger.Sync()
    logger.Info("my log msg")
    // ...
}

Output:
err creating logger: open sink "/output.log": open /output.log: permission denied

[oernii]

That worked nicely, thanks for the hint.