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Lazy values not set

Description​

Exploit Scenario​

Consider the following contract:

    #[ink(storage)]
    pub struct Contract {
        mapping: Mapping<AccountId, u64>,
    }
    impl Contract {
        /* --- snip --- */
        #[ink(message)]
        pub fn sum(&mut self, value: u64) -> Result<(), Error> {
            let key = self.env().caller();
            let mut _val = self.mapping.get(key).unwrap_or_default();
            _val += value;
            Ok(())
        }
        /* --- snip --- */
    }

In this case, when you .get(...) a value from a Lazy storage field, you probably want to mutate it. The values are not automatically flushed to storage, so you need to .set(...) it.

Remediation​

Use the .set(...) or .insert(...) method after using .get(...) to flush the new value to storage.

    #[ink(storage)]
    pub struct Contract {
        mapping: Mapping<AccountId, u64>,
    }
    impl Contract {
        /* --- snip --- */
        #[ink(message)]
        pub fn sum(&mut self, value: u64) -> Result<(), Error> {
            let key = self.env().caller();
            let mut _val = self.mapping.get(key).unwrap_or_default();
            _val += value;
            self.mapping.insert(key, value);
            Ok(())
        }
        /* --- snip --- */
    }

Known Issues​

If you have a .get(...) function that you don't mutate (e.g., used as a const value), this detector triggers, if you want to ignore the lint you could add #[allow(lazy_values_not_set)] immediately before the function definition.