Simplify a Unix-style absolute path
The () is not needed in this example - the following example compiles fine.
match line {
    &quot;&quot; | &quot;.&quot; =&gt; {}
    &quot;..&quot; =&gt; {
        str_vec.pop();
    }
    _ =&gt; str_vec.push(line),
}

This is as all arms need to return the same type, and in this case it is the type (). Luckily this type is inferred, and as such you can just make a block and (as long as it doesn't return anything), it will be inferred that the () type is being returned instead.
I would recommend making some other changes to your code though - namely changing the &amp;String argument to &amp;str, which can improve performance in some cases and allow more string types (such as a string literal) to be passed to the function. This type of issue can be picked up by running clippy, which also picks up a wide variety of issues - a full list can be found at https://rust-lang.github.io/rust-clippy/master/.