How to update self based on reference of value from hashmap from self

use std::collections::HashMap;
use std::collections::hash_map::Entry::*;

struct A {
    map: HashMap<String, String>,
    i: i32
}
impl A {
    fn test(&mut self) {
        match self.map.get("abc") {
            None => {},
            Some(x) => self.trigger(&x)
        }
    }

    fn trigger(&mut self, x: &str) {
        self.i += 1;
    }
}

The code doesn't work because self.trigger borrows self mutably, while self.map.get is keeping an immutable borrow of self in scope.

Is there any way to make it work, given that I can make sure in the trigger I don't modify self.map?

I cannot make trigger borrow self immutably, as in Can I borrow self immutably for self.callbacks: Vec<Box<FnMut>>?

I'm using rustc 1.19.0-nightly.