Bad suggestion of `useless_let_if_seq` when having side effects.

The version of clippy is 0.0.212.

Here's an example:

pub fn func() {
    // This need to be called first always.
    let mut ret = foo1();
    if cond() {
        // Overwrite with some complex expr.
        ret = (foo2() * 2).to_string().len() as _;
    }
    
    baz(ret)
}

It suggest writing let <mut> ret = if cond() { .. foo2() .. } else { foo1() };, which cause 3 function calls (may have side-effects) being reordered, and foo1() not always being called.

Well, I'm not sure how to write make it more idiomatic in this case...

Start by reproducing the useless_let_if_seq suggestion with the Rust example in the issue, using cargo clippy. Read the lint implementation and its existing tests to determine how side effects and evaluation order are handled; done means the example no longer receives an unsafe or misleading suggestion while valid cases still do.