Why am I getting a \"Using the variable on range scope x in function literal\" error in Go?

Using Variables on Range Scope x in Function Literals

Problem:

In the following code snippet, the go vet tool is reporting an error: "Using the variable on range scope x in function literal (scopelint)".

<code class="go">func TestGetUID(t *testing.T) {
    for _, x := range tests {
        t.Run(x.description, func(t *testing.T) {
            client := fake.NewSimpleClientset(x.objs...)
            actual := getUID(client, x.namespace)
            assert.Equal(t, x.expected, actual)
        })
    }
}</code>

Explanation:

The error message indicates that x, which is a loop variable, is being used in a function literal that is passed to t.Run(). The compiler cannot guarantee that the function literal will not be called after t.Run() returns, which could lead to a data race or other unexpected behavior.

Solution:

To resolve this issue, you can make a copy of x and use that copy in the function literal:

<code class="go">func TestGetUID(t *testing.T) {
    for _, x := range tests {
        x2 := x // Copy the value of x
        t.Run(x2.description, func(t *testing.T) {
            client := fake.NewSimpleClientset(x2.objs...)
            actual := getUID(client, x2.namespace)
            assert.Equal(t, x2.expected, actual)
        })
    }
}</code>

Alternatively, you can shadow the loop variable x by assigning it to a new variable of the same name within the function literal:

<code class="go">func TestGetUID(t *testing.T) {
    for _, x := range tests {
        t.Run(x.description, func(t *testing.T) {
            x := x // Shadow the loop variable
            client := fake.NewSimpleClientset(x.objs...)
            actual := getUID(client, x.namespace)
            assert.Equal(t, x.expected, actual)
        })
    }
}</code>

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