CodeQL documentation

Whitespace contradicts operator precedence

ID: go/whitespace-contradicts-precedence
Kind: problem
Severity: warning
Precision: very-high
Tags:
   - maintainability
   - correctness
   - external/cwe/cwe-783
Query suites:
   - go-security-and-quality.qls

Click to see the query in the CodeQL repository

Nested expressions where the spacing around operators suggests a different grouping than that imposed by the Go operator precedence rules are problematic: they could indicate a bug where the author of the code misunderstood the precedence rules. Even if there is no a bug, the spacing could be confusing to people who read the code.

Recommendation

Make sure that the spacing around operators reflects operator precedence, or use parentheses to clarify grouping.

Example

Consider the following function intended for checking whether the bit at position `pos` of the variable `x` is set:

package main

func isBitSetBad(x int, pos uint) bool {
	return x&1<<pos != 0
}

Here, the spacing around & and << suggests the grouping x & (1<<pos). However, in Go & and << have the same precedence and hence are evaluated left to right, so the expression is actually equivalent to (x & 1) << pos.

To fix this issue and give the expression its intended semantics, parentheses should be used like this:

package main

func isBitSetGood(x int, pos uint) bool {
	return x&(1<<pos) != 0
}

References