False positive: print_literal and env!

[bjgill]

Found with clippy 0.0.193

warning: printing a literal with an empty format string
  --> src/bin/rm/main.rs:92:41
   |
92 |         println!("cargo-rm version {}", env!("CARGO_PKG_VERSION"));
   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(print_literal)] on by default
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.193/index.html#print_literal

I'm fairly certain that there isn't a way to shorten this as the docs suggest.

It looks as if this was discussed in #2617 and #2608. Whilst it's true that println!(env!("FOO")) is better than println!("{}", env!("FOO")), I don't think there is an equivalent for println!("bar: {}", env!("FOO")).

[mrecachinas]

Yeah this is a tricky one... using a late pass converts all macros, so env!(“FOO”) looks like a string by the time the print_literal check happens.

[mrecachinas]

@oli-obk @phansch So I looked a bit more into this. I added a test for env!("FOO") where I've defined "$FOO" to be "test" (export FOO=test). As expected, the test yielded a false positive:

error: printing a literal with an empty format string
  --> tests/ui/print_literal.rs:40:25
   |
40 |     println!("ENV: {}", env!("FOO"));
   |                         ^^^^^^^^^^^

I then tried to inspect what's going on as well as use utils::{in_macro}. Unfortunately, in_macro is false for the exact span that gets warned in the lint.

Looking into the args at the time it's linted in write.rs, you can see expr(896: &match (&"test",) ...)

[expr(885: &["ENV: ", "\n"]), expr(896: &match (&"test",) {
     (__arg0,) => [<::fmt::ArgumentV1>::new(__arg0, ::fmt::Display::fmt)],
 }), expr(908: &[::fmt::rt::v1::Argument{position: ::fmt::rt::v1::Position::At(0usize),
                          format:
                              ::fmt::rt::v1::FormatSpec{fill: ' ',
                                                        align:
                                                            ::fmt::rt::v1::Alignment::Unknown,
                                                        flags: 0u32,
                                                        precision:
                                                            ::fmt::rt::v1::Count::Implied,
                                                        width:
                                                            ::fmt::rt::v1::Count::Implied,},}])]

I'm very curious what the way to proceed here would be. I'm thinking this might require an EarlyLintPass, but I'm not entirely sure how to chain both together.

[oli-obk]

I assumed I fixed this with rust-lang/rust#44248

Maybe it regressed again in rustc?

[mbr]

Still present on rustc 1.29.0-nightly (64f7de9 2018-07-12), clipp 0.0.211.

[phansch]

I can't reproduce this on the playground anymore, so I'm going ahead and will close this issue. Feel free to re-open if this still happens with a recent Clippy version.