CodeQL documentation

Comparison of identical values

ID: go/comparison-of-identical-expressions
Kind: problem
Severity: warning
Precision: very-high
   - correctness
   - external/cwe/cwe-570
   - external/cwe/cwe-571
Query suites:
   - go-security-and-quality.qls

Click to see the query in the CodeQL repository

Comparing two identical expressions typically indicates a mistake such as a missing qualifier or a misspelled variable name.


Carefully inspect the comparison to determine whether it is a symptom of a bug.


In the example below, the method Rectangle.contains is intended to check whether a point (x, y) lies inside a rectangle r given by its origin (r.x, r.y), its width r.width, and its height r.height.

package main

type Rectangle struct {
	x, y, width, height float64

func (r *Rectangle) containsBad(x, y float64) bool {
	return r.x <= x &&
		y <= y &&
		x <= r.x+r.width &&
		y <= r.y+r.height

Note, however, that on line 9 the programmer forgot to qualify r.y, thus ending up comparing the argument y against itself. The comparison should be fixed accordingly:

package main

func (r *Rectangle) containsGood(x, y float64) bool {
	return r.x <= x &&
		r.y <= y &&
		x <= r.x+r.width &&
		y <= r.y+r.height
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