From the documentation:

It is also possible to have local variables with static lifetime by using containers inside functions.

const std = @import("std");
const expect = std.testing.expect;

test "static local variable" {
    try expect(foo() == 1235);
    try expect(foo() == 1236);
}

fn foo() i32 {
    const S = struct {
        var x: i32 = 1234;
    };
    S.x += 1;
    return S.x;
}

Doesn’t this essentially make S inside foo a static variable with static memory storage as if it were declared in the file scope, but whose scope is simply limited to foo?