Set the file extension in Rust

The PathBuf struct has a method called set_extension. One would thing that it is the tool that we always need to use to, well, set the extension of a file.

Unfortunately it has some caveats. Specifically that if the file has a dot in it, the set_extension will consider the part after the last dot as the current extension and it will replace it with the new one.

So when I was working on the MSRV report of the Rust Digger this created a mess.

It took me some time to understand the problem and then went for the axe, or at least the format! macro that you can also see in the examples:

examples/set-file-extension/src/main.rs

fn main() {
    let mut path = std::path::PathBuf::from("hello");
    println!("{:?}", path); // "hello"

    // adds an extension
    path.set_extension("txt");
    println!("{:?}", path); // "hello.txt"

    // replaces an extension
    path.set_extension("html");
    println!("{:?}", path); // "hello.html"

    // If we have a file that has a . in the name, for example
    let mut path = std::path::PathBuf::from("hello.0");
    println!("{:?}", path); // "hello.0"

    // and we would like to add an extension, this will not do what we
    // want as this will replace the 0 by the html
    path.set_extension("html");
    println!("{:?}", path); // "hello.html"

    let path = std::path::PathBuf::from("hello.0");
    println!("{:?}", path); // "hello.0"
    println!("{}", format!("{}.html", path.display())); // hello.0.html

    let path = std::path::PathBuf::from(format!("{}.html", path.display()));
    println!("{:?}", path); // "hello.0.html"
}