Lint for missing storage write-back

[ggwpez]

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Often a storage value is first loaded, modify it and then hopefully written back to storage. A lint could be added which checks that modified values from storage are written back. Example:

let mut val = Value::<T>::get();
val += 123;
…
Value::<T>::set(&val); // Errors if this line is missing.

No idea how difficult that is to implement, just wanted to drop that idea.