nilness

Overview ¶

Package nilness inspects the control-flow graph of an SSA function and reports errors such as nil pointer dereferences and degenerate nil pointer comparisons.

Analyzer nilness ¶

nilness: check for redundant or impossible nil comparisons

The nilness checker inspects the control-flow graph of each function in a package and reports nil pointer dereferences, degenerate nil pointers, and panics with nil values. A degenerate comparison is of the form x==nil or x!=nil where x is statically known to be nil or non-nil. These are often a mistake, especially in control flow related to errors. Panics with nil values are checked because they are not detectable by

if r := recover(); r != nil {

This check reports conditions such as:

if f == nil { // impossible condition (f is a function)
}

and:

p := &v
...
if p != nil { // tautological condition
}

and:

if p == nil {
	print(*p) // nil dereference
}

and:

if p == nil {
	panic(p)
}

Sometimes the control flow may be quite complex, making bugs hard to spot. In the example below, the err.Error expression is guaranteed to panic because, after the first return, err must be nil. The intervening loop is just a distraction.

...
err := g.Wait()
if err != nil {
	return err
}
partialSuccess := false
for _, err := range errs {
	if err == nil {
		partialSuccess = true
		break
	}
}
if partialSuccess {
	reportStatus(StatusMessage{
		Code:   code.ERROR,
		Detail: err.Error(), // "nil dereference in dynamic method call"
	})
	return nil
}

...