ch07-03-paths-for-referring-to-an-item-in-the-module-tree: field is never read: seasonal_fruit note: #[warn(dead_code)] on by default

[HenrikBach1]

URL to the section(s) of the book with this problem:
https://doc.rust-lang.org/book/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html

Description of the problem:
Listing 7-9 cannot compile, even though you create a main function calling the function eat_at_restaurant, due to the compiler complaints about the seasonal_fruit field of Breakfast:

[{
	"resource": "/projects/rust/paths-in-modules-7_3/src/main.rs",
	"owner": "rust-file:///projects/rust/paths-in-modules-7_3",
	"code": "dead_code",
	"severity": 4,
	"message": "field is never read: `seasonal_fruit`\n\nnote: `#[warn(dead_code)]` on by default",
	"source": "rustc",
	"startLineNumber": 4,
	"startColumn": 9,
	"endLineNumber": 4,
	"endColumn": 31
}]

vscode ➜ /projects/rust/paths-in-modules-7_3 (master ✗) $ rustc --version
rustc 1.59.0 (9d1b2106e 2022-02-23)

Complete code:

mod back_of_house {
    pub struct Breakfast {
        pub toast: String,
        seasonal_fruit: String,
    }

    impl Breakfast {
        pub fn summer(toast: &str) -> Breakfast {
            Breakfast {
                toast: String::from(toast),
                seasonal_fruit: String::from("peaches"),
            }
        }
    }
}

pub fn eat_at_restaurant() {
    // Order a breakfast in the summer with Rye toast
    let mut meal = back_of_house::Breakfast::summer("Rye");
    // Change our mind about what bread we'd like
    meal.toast = String::from("Wheat");
    println!("I'd like {} toast please", meal.toast);

    // The next line won't compile if we uncomment it; we're not allowed
    // to see or modify the seasonal fruit that comes with the meal
    // meal.seasonal_fruit = String::from("blueberries");
}

fn main ()
{
    eat_at_restaurant()
}

Suggested fix:

[MarkDBlackwell]

Listing 7-9 should be prepended with #![allow(dead_code)] similar to #3081.

[carols10cents]

Hi, please search existing issues before filing new issues. If you had searched dead_code, you would have found this issue and others where I responded:

There are many examples in the book that will get dead code warnings because we are showing small pieces as digestible examples, not full production code. Thanks though!

[MarkDBlackwell]

@carols10cents Thank you for all your wonderful work!

Would you welcome a single pull request prepending relevant allow statements to each listing? :)

I feel it would improve the readers' experience to prevent all these warnings. Please let me know!

[carols10cents]

No, I think it would be distracting.

[MarkDBlackwell]

The emitted warnings would be better addressed by mdBook—I found a relevant issue.

[HenrikBach1]

Hi,

The problem is not with the "dead" code and elimination of it. The problem is that the compiler emits, in my opion, an error error that is not true, due to that the field of the struct is used later in the code.

Maybe, this wasn't the right forum to discuss this issue in...?

[HenrikBach1]

Above issue is now reported in: rust-lang/rust#95105

Thank you for your response.