Unsigned Negative Comparison

ID

go.unsigned_negative_comparison

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Go

Tags

reliability, suspicious-comparison

Description

Reports a relational comparison between an unsigned-typed operand and a negative integer literal, such as u < -1 or u >= -1.

Rationale

An unsigned integer can never hold a negative value, so a comparison against a negative literal has a constant result: u < -1 (and u ⇐ -1, u == -1) is always false, while u >= -1 (and u > -1, u != -1) is always true. The code reads as a real test but does nothing — a guard that fails to reject anything, or a condition that is always taken. It is almost always a logic error, often caused by forgetting that the variable is unsigned.

func check(u uint) {
    if u < -1  { ... } // FLAW — always false
    if u >= -1 { ... } // FLAW — always true
    if u < 5   { ... } // OK
}

Remediation

Reconsider the intended bound. If the value should be tested for zero, compare against 0 (u == 0); if the variable can legitimately be negative, change its type to a signed integer.

References