indoc 0.2 doesn't work with format!() anymore

[Boscop]

I was using indoc 0.1.15 for this function:

fn send_pretty(user: &User, subject: &str, body: &str) -> Result<(), &'static str> {
    use std::iter::repeat;

    send_email(&user.email, subject, &format!(indoc!("
        Hello {username}
        ======{underline}

        {body}
    "),
        username = user.name,
        underline = repeat('=').take(user.name.len()).collect::<String>(),
        body = body
    ))
}

Now that I updated to indoc 0.2 it doesn't work anymore:

error: src\mail.rs:39: format argument must be a string literal.

It seems that indoc!() doesn't return a string literal anymore.

[dtolnay]

Thanks for reporting this! I didn't think of this case. I don't think there is a way to make it work on the stable compiler but I published 0.2.1 with an optional unstable feature to use Macros 2.0 in a way that format! should work.

[dependencies]
indoc = { version = "0.2.1", features = ["unstable"] }

#![feature(proc_macro)]

extern crate indoc;
use indoc::indoc;

fn main() {
    let s = format!(indoc!("{}"), true);
    assert_eq!(s, "true");
}

[Boscop]

Hm, I still get the same error when I use #![feature(proc_macro)] and extern crate indoc;
(Before, with version 0.1.15, I had #![plugin(indoc)] and no extern crate)
When I write #[macro_use] extern crate indoc; I get:

error: src\mail.rs:10: procedural macros cannot be imported with #[macro_use]
help: src\mail.rs:10: instead, import the procedural macro like any other item: use indoc_impl::indoc;

[dtolnay]

Macros 2.0 macros are imported differently. Check out the code in my previous comment.

[dtolnay]

If you get the same "format argument must be a string literal" error with indoc 0.2.1 with the unstable feature enabled and imported with use indoc::indoc, could you share the full nonworking code?

[Boscop]

Ah, I hadn't seen use indoc::indoc;. Now it works, thanks :)
Does that mean the indoc macro will never work with format!() on stable Rust from now on?

[dtolnay]

The indoc macro has never worked as a format string on stable Rust in the past, and it will continue to not work as a format string on stable Rust until the Macros 2.0 feature is stabilized. Other uses of indoc will work on stable Rust >=1.15.0 as of indoc 0.2.