rust/tests/ui/fmt/format-args-capture.rs

// run-pass

fn main() {
    named_argument_takes_precedence_to_captured();
    formatting_parameters_can_be_captured();
    capture_raw_strings_and_idents();
    repeated_capture();

    #[cfg(panic = "unwind")]
    {
        panic_with_single_argument_does_not_get_formatted();
        panic_with_multiple_arguments_is_formatted();
    }
}

fn named_argument_takes_precedence_to_captured() {
    let foo = "captured";
    let s = format!("{foo}", foo = "named");
    assert_eq!(&s, "named");

    let s = format!("{foo}-{foo}-{foo}", foo = "named");
    assert_eq!(&s, "named-named-named");

    let s = format!("{}-{bar}-{foo}", "positional", bar = "named");
    assert_eq!(&s, "positional-named-captured");
}

fn capture_raw_strings_and_idents() {
    let r#type = "apple";
    let s = format!(r#"The fruit is an {type}"#);
    assert_eq!(&s, "The fruit is an apple");

    let r#type = "orange";
    let s = format!(r"The fruit is an {type}");
    assert_eq!(&s, "The fruit is an orange");
}

#[cfg(panic = "unwind")]
fn panic_with_single_argument_does_not_get_formatted() {
    // panic! with a single argument does not perform string formatting.
    // RFC #2795 suggests that this may need to change so that captured arguments are formatted.
    // For stability reasons this will need to part of an edition change.

    #[allow(non_fmt_panics)]
    let msg = std::panic::catch_unwind(|| {
        panic!("{foo}");
    })
    .unwrap_err();

    assert_eq!(msg.downcast_ref::<&str>(), Some(&"{foo}"))
}

#[cfg(panic = "unwind")]
fn panic_with_multiple_arguments_is_formatted() {
    let foo = "captured";

    let msg = std::panic::catch_unwind(|| {
        panic!("{}-{bar}-{foo}", "positional", bar = "named");
    })
    .unwrap_err();

    assert_eq!(msg.downcast_ref::<String>(), Some(&"positional-named-captured".to_string()))
}

fn formatting_parameters_can_be_captured() {
    let width = 9;
    let precision = 3;

    let x = 7.0;

    let s = format!("{x:width$}");
    assert_eq!(&s, "        7");

    let s = format!("{x:<width$}");
    assert_eq!(&s, "7        ");

    let s = format!("{x:-^width$}");
    assert_eq!(&s, "----7----");

    let s = format!("{x:-^width$.precision$}");
    assert_eq!(&s, "--7.000--");
}

fn repeated_capture() {
    let a = 1;
    let b = 2;
    let s = format!("{a} {b} {a}");
    assert_eq!(&s, "1 2 1");
}