Meh, this is actually a pattern I've seen used often and it's okay IMO (esp. for test imports).

Allow fine though

I feel that at least function-local should be allowed if at the top of the function.

(esp. for test imports).

We probably should ignore use statements within #cfg(test) (or perhaps any #cfg).

I'm fine with Allow.

And again, we can have multiple lints ranging from pedantic to lenient.

Turns out use isn't even allowed in blocks if not at the start...

Yeah, but there can be a lot of blocks within a function...

@llogiq: what is the undesirable effect of a use inside e.g. a loop block?

Is it possible to elaborate a bit why this is bad? Doing it could enhance self-containedness of functions. Not to say I don't empathize with your apprehension ...

We'll focus on "module-level use statements should not come after other items"

Hey, I wanted to work on this as a first issue, if this is still wanted and no one else is working on it; I'd be glad to. Please let me know the current status of this issue.

Sure, feel free to claim the issue (see the CONTRIBUTING.md file) if you want to work on it!

@rustbot claim

running TESTNAME=items_before_use cargo uibless or TESTNAME=items_before_use cargo bless generating stderr file as visible in the full stderr section of the output. But when i run TESTNAME=items_before_use cargo test it fails.

As i can notice the test run emits diagnostic labels like Error[clippy::items_before_use], and "unmatched diagnostics" which might be causing the test to fail. But I'm not sure since this is my first time writing a lint for clippy.

I apologize if this was a dumb question but it has really been bugging me. Any guidance will be much appreciated.

Output:

error: there were 1 unmatched diagnostics
 --> tests/ui/items_before_use.rs:6:1
  |
6 | use std::fmt; // Should trigger lint
  | ^^^^^^^^^^^^^ Error[clippy::items_before_use]: module level use statements should precede all items
  |

error: there were 1 unmatched diagnostics
 --> tests/ui/items_before_use.rs:7:1
  |
7 | use std::io; // Should also trigger lint
  | ^^^^^^^^^^^^ Error[clippy::items_before_use]: module level use statements should precede all items
  |

error: there were 1 unmatched diagnostics
  --> tests/ui/items_before_use.rs:12:5
   |
12 |     use std::fs; // Should trigger lint
   |     ^^^^^^^^^^^^ Error[clippy::items_before_use]: module level use statements should precede all ite
ms
   |

error: expected error patterns, but found none

full stderr:
error: module level use statements should precede all items
  --> tests/ui/items_before_use.rs:6:1
   |
LL | use std::fmt; // Should trigger lint
   | ^^^^^^^^^^^^^
   |
   = note: consider moving this statement to the top of the module.
   = note: `-D clippy::items-before-use` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::items_before_use)]`

error: module level use statements should precede all items
  --> tests/ui/items_before_use.rs:7:1
   |
LL | use std::io; // Should also trigger lint
   | ^^^^^^^^^^^^
   |
   = note: consider moving this statement to the top of the module.

error: module level use statements should precede all items
  --> tests/ui/items_before_use.rs:12:5
   |
LL |     use std::fs; // Should trigger lint
   |     ^^^^^^^^^^^^
   |
   = note: consider moving this statement to the top of the module.

error: aborting due to 3 previous errors


full stdout:


FAILURES:
    tests/ui/items_before_use.rs

test result: FAIL. 1 failed; 1086 filtered out


thread 'main' panicked at tests/compile-test.rs:222:6:
called `Result::unwrap()` on an `Err` value: tests failed

Location:
    /home/kin/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.29.2/src/lib.rs:369:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: test failed, to rerun pass `--test compile-test`
[kin@arch rust-clippy]$ 

I think this is a solution without a problem.

@llogiq: what is the undesirable effect of a use inside e.g. a loop block?

Is it possible to elaborate a bit why this is bad? Doing it could enhance self-containedness of functions. Not to say I don't empathize with your apprehension ...

If imports come after their usage, that would be unintuitive. I believe that is only possible with module-level imports.

Could the arbitrary_source_item_ordering lint help with this? The lint can enforce that all use items appear before functions, const, statics, ...

imports are items, so that would make sense!

Any guidance will be much appreciated.

If this issue/lint is no longer required or seems a redundant add, I'm happy to drop this issue.

But if not, any help as to why my test was doing that would be appreciated. Any maintainer reading this issue can pass the final verdict, Thanks again.

As for your error, try adding proper error markers to the lines where you expect your lint to emit. So for example on line 6 (based on your stderr output), write use std::fmt; //~ items_before_use (instead of a normal comment saying "should trigger lint").

That said, IMHO it does sound like the lint arbitrary_source_item_ordering already pretty much covers the use case "module-level use statements should not come after other items". With that lint you can specify an item order that clippy should enforce, so it's a more general version of this.
I think it's also pretty standard for mod and extern crate items to appear before use items, I'm not sure if this lint would make an exception and allow those?

Thanks for the help @y21, The tests all passed and I've declared two lints, one pedantic that is opt-in and stricter which will ask for use statements to be at the absolute top while the other is a style which will ignore mod and extern crates as you mentioned.

We probably should ignore use statements within #cfg(test) (or perhaps any #cfg).
And again, we can have multiple lints ranging from pedantic to lenient.

I still struggled to figure out a solution for the cfg blocks as the author of this issue asked. I've tried multiple methods under cx.tcx. Multiple ways (get_attrs, matches, hir_attrs). But my test for the cfg block still failed

mod test2 {
    fn name() {}
    // use inside cfg block, should be ignored
    #[cfg(feature = "foo")]
    fn baz() {}
    use std::collections::HashMap;
}

error: there were 1 unmatched diagnostics
  --> tests/ui/items_before_use.rs:14:5
   |
14 |     use std::collections::HashMap;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Error[clippy::items_before_use]: module level use statements shou
ld precede all items
   |

All other tests passed and behaved as expected.
Is anyone aware of methods to accurately check for attributes of items under a cfg block? Thanks.

Module-level use statements are items.

Module-level use statements are items.

I'm aware.. The lint should be "module level use statements should precede all other items". The error says "all items" because it's still WIP, My apologies for that.

I used ItemKind enum to do the basic work

            match item.kind {
                ItemKind::Use(..) => {
                    if saw_non_use {
                        span_lint_and_note(
                            cx,
                            ITEMS_BEFORE_USE,
                            item.span,
                            "module level use statements should precede all other items",
                            None,
                            "consider moving this statement to the top of the module.",
                        );
                    }
                },
                _ => saw_non_use = true,
            }