Rust-clippy: suggest omitting formatting when printing string literals

[matthiaskrgr]

instead of
rust println!("{}", "Hello world");
suggest
rust println!("Hello world");
which can be noticeably faster
test tests::bench_inline ... bench: 46,300 ns/iter (+/- 2,643) test tests::bench_inline_format ... bench: 78,796 ns/iter (+/- 10,303)

[mrecachinas]

@matthiaskrgr I'd like to take a stab at this if you don't mind!

[matthiaskrgr]

I do absolutely not mind :D

[matthiaskrgr]

Btw I just saw there already is a format!("{}", "bla"); lint here: https://github.com/rust-lang-nursery/rust-clippy/blob/master/clippy_lints/src/format.rs#L39

maybe it's possible to reuse some code :)

[mrecachinas]

Thanks for pointing me to that! I had been looking at print.rs.

I'll try to get something you can take a look at tonight/tomorrow. I'm starting with the simple case:

println!("{}", "foo");

but I imagine we'll want to parse the args for the general case

println!("{} {}", some_var, "foo");

[matthiaskrgr]

Yeah, if we have
println!("{} {}", some_var, "foo");
we could inline like this:
println!("{} foo", some_var);

[mrecachinas]

@matthiaskrgr See #2608 -- sorry for the delay!

[matthiaskrgr]

Looks like it's working fine, closing the ticket =)