False positive for a nil channel select case

[sonalmahajan15]

Although a direct send/receive on a nil channel can cause a panic, the following code with use of select is safe. However, NilAway still reports an error.

func foo(aChan, bChan chan string) {
	aChan <- "abc"
	bChan <- "xyz"

	if true {
		aChan = nil
	}

	select {
	case a := <-aChan:   // error: "literal `nil` uninitialized; nil channel accessed"
		print(a)
	case b := <-bChan:
		print(b)
	}
}

func test() {
	aChan := make(chan string)
	bChan := make(chan string)

	go foo(aChan, bChan)
}

[bokwoon95]

Although a direct send/receive on a nil channel can cause a panic

Actually, both writing and reading on a nil channel never panics 🙂. Not just on select. Here is some code to replicate:

package main

import (
    "fmt"
    "time"
)

func main() {
    var aChan chan string = nil
    // Write to a nil channel; does not panic, blocks forever.
    go func() {
        aChan <- "sendValue"
    }()
    // Read from a nil channel; does not panic, blocks forever.
    go func() {
        receiveValue := <-aChan
        fmt.Println(receiveValue)
    }()
    // Print an empty string to console every 5 seconds to prevent deadlock.
    for {
        time.Sleep(5 * time.Second)
        fmt.Print("")
    }
}

[orsinium]

Here is a convenient table from "Concurrency in Go" of how each channel operation behaves on each channel type. As you can see, only closing a nil channel may cause panic.

[roma-glushko]

Is there a way to ignore a specific line where the error happens? I have tried nolint:nilaway but that did not help 😞

[sonalmahajan15]

Is there a way to ignore a specific line where the error happens? I have tried nolint:nilaway but that did not help 😞

@roma-glushko: If you are using the standalone go/analysis driver, then unfortunately //nolint:nilaway is not currently supported. In principle, we believe that enabling this support falls under the responsibility of the driver, as demonstrated by the support provided by nogo. Nevertheless, we have it on the roadmap to implement this support within NilAway itself to make it driver independent. (You can refer to #143 (comment) for more context.)