Add a lint for items used before definition,inside expression block

[rodrimati1992]

I would like to have a lint like the items_after_statements lint,but which only triggers if an item defined inside an expression block is used before it's defined.

For example,it would trigger with this code:

fn hello() {
    println!("First statement");
    let hello: Bar = (0..10).collect();
    type Bar = Vec<u32>;
}

But it would not trigger with this code:

fn hello() {
    println!("First statement");
    type Bar = Vec<u32>;
    let hello: Bar = (0..10).collect();
}

[DevAccentor]

@rustbot claim

[DevAccentor]

The lint already exists and does that. The issue can be closed.

[Rqnsom]

Can confirm. This is covered by clippy::items-after-statements. We can close this issue

EDIT:
no! I just re-read the whole proposal and seems like this would be a complete new lint. Which sort of collides with clippy::items-after-statements in a sense that if one fixes clippy::items-after-statements, then this new lint would be automatically fixed.

We could call it clippy::declare-items-before-usage maybe?

Recap:

Example 1

fn hello() {
    println!("First statement");
    let hello: Bar = (0..10).collect();
    type Bar = Vec<u32>;
}

This code would trigger clippy::declare-items-before-usage and clippy::items-after-statements.

Example 2

fn hello() {
    println!("First statement");
    type Bar = Vec<u32>;
    let hello: Bar = (0..10).collect();
}

This code would trigger only clippy::items-after-statements.

Example 3

fn hello() {
    type Bar = Vec<u32>;
    println!("First statement");
    let hello: Bar = (0..10).collect();
}

This code wouldn't trigger any lint.

[xFrednet]

So, this lint proposal is basically just a lighter version of clippy::items-after-statements. Adding a new lint for this SGTM. Though I would suggest a different name, since clippy::declare-items-before-usage doesn't work too well with lint attributes: #[deny(clippy::declare-items-before-usage)] does exactly the opposite of what it says. clippy::items-before-usage would be good IMO. Also, because it's similar to the other lint 🙃

[flip1995]

I would extend this lint with a configuration option, to only warn if the item is used before. This configuration should be turned off by default to keep the current behavior.