Use if-let chains when available to clean up some code

[marco-c]

rust-lang/rust#53667

[ghost]

Hey @marco-c, curious about any performance or stylistic improvements for doing this. My understanding of if-let's are primarily for handling a single match pattern and ignoring the rest. As I look through the codebase, most comparisons seem to have two match patterns, e.g. in lib.rs:

match result.lines.entry(line_no) {
       btree_map::Entry::Occupied(c) => {
           *c.into_mut() += execution_count;
       }
       btree_map::Entry::Vacant(v) => {
           v.insert(execution_count);
       }
};

I could change that to and if-let like so:

if let btree_map::Entry::Occupied(c) = result.lines.entry(line_no) {
       *c.into_mut() += execution_count;
}
if let btree_map::Entry::Vacant(v) = result.lines.entry(line_no) {
       v.insert(execution_count);
}

Is this just the preferred syntax now, or are there performance improvements? Happy to start contributing to this project with this (feel free to assign to me), just wondering to get feedback on any technical improvements I don't know about or if this was just stylistic preference.

Cheers!

[marco-c]

It's just a stylistic preference, but not to apply in cases like the one you mentioned.

A good example is

grcov/src/gcov.rs

Line 7 in 5d6715d

match env::var("GCOV") {

, where:

    match env::var("GCOV") {
        Ok(s) => s,
        Err(_) => "gcov".to_string(),
    }

would become:

if let Ok(s) = env::var("GCOV") {
  s
} else {
  "gcov".to_string()
}

[ghost]

Great, thanks for the feedback. I'll take a shot at this and open a PR shortly. Thanks!