Some diesel trait resolution remains broken

[weiznich]

rust-analyzer version: rust-analyzer 0.3.1481-standalone (I've downloaded this release)

rustc version: rustc 1.68.0 (2c8cc3432 2023-03-06)

relevant settings: None non-standard settings

Rust analyzer fails to infer some diesel trait bounds even after applying a workaround for the previous name resolution bug. It seems to correctly pick up some of the diesel provided traits, but fails on others. It's unclear why some work, while others remain broken even if they use similar implementation patterns. For example this impl in diesel works, while this won't work. I'm happy to provide more information here if someone points out what might be helpful.

This results in no type hints being shown and no completions being suggested after one of the failing trait methods is used.

Code to reproduce the issue:

[dependencies]
# this version already contains the workaround for the rust-analyzer name resolution "bug"
diesel = { version = "=2.0.4", features = ["sqlite"], default-features = false }

use diesel::prelude::*;

table! {
    users {
        id -> Integer,
        name -> Text,
    }
}

table! {
    posts {
        id -> Integer,
        user_id -> Integer,
    }
}

allow_tables_to_appear_in_same_query!(users, posts);
joinable!(posts -> users (user_id));

#[derive(Selectable, Queryable)]
struct User {
    id: i32,
}

fn main() {
    let conn = &mut SqliteConnection::establish("_").unwrap();

    // these QueryDsl methods work
    let u = users::table
        .limit(10)
        .offset(15)
        .distinct()
        .order_by(users::id)
        .group_by(users::id)
        .then_order_by(users::name)
        .having(users::id.eq(42))
        .select(users::id)
        .load::<i32>(conn);

    // these queries don't work
    let u = users::table
        .inner_join(posts::table)
        .load::<((i32, String), (i32, i32))>(conn);

    let u = users::table
        .left_join(posts::table)
        .load::<((i32, String), Option<(i32, i32)>)>(conn);

    let u = users::table
        .filter(users::id.eq(42))
        .load::<(i32, String)>(conn);

    let u = users::table
        .find(42)
        .load::<(i32, String)>(conn);

    let u = users::table.select(User::as_select()).load(conn);

}

Inferred Types:

[lowr]

One of the ultimate causes of this bug is same as #14369, for which I submitted rust-lang/chalk#792. Because of this, chalk fails to normalize <posts::table as diesel::JoinTo<users::table>>::OnClause and other similar projections that are generated by the joinable! macro.

Note that rust-lang/chalk#792 only fixes some issues and introduces a few new type mismatches (see the image below taken with my custom-built rust-analyzer with the chalk patch applied). I had analyzed this regression before submitting the patch, and it's not because the patch is wrong, I believe, but because it uncovers another consequence of rust-lang/chalk#584. I'd rather not write in details on this as it's complicated, though I can provide more info if necessary.

It's really not human friendly, but here's a gist with chalk's debug log I analyzed if anyone's interested.

[boehs]

Is there a version of rust analyzer where this works?

[AJTJ]

I would like to bump this, as having to estimate types in Diesel is rather frustrating.

[AJTJ]

@weiznich I see that you say this current bug is rust-analyzer's issue here: https://github.com/diesel-rs/diesel/commit/74f301b493074378b6ef616885f6e501b6567b58 And you mention that this is because of rust-analyzer lacking compatibility with the 2015 name style resolution here: https://github.com/rust-lang/rust-analyzer/issues/12589#issuecomment-1486772094

If you are confident this is the case, can we link to that issue/missing feature here?

[Veykril]

The remaining resolution errors here are not due to the 2015 name resolution being missing in r-a as diesel no longer uses that. There are some other type inference problems in r-a here that cause the remaining ones.

[AJTJ]

Welp, I don't think I'm doing this wrong, but there are times when I'm getting absolutely no help.

@Veykril do we have an idea what's wrong? Can I help?

[Veykril]

lowr pointed some of the issues out https://github.com/rust-lang/rust-analyzer/issues/14607#issuecomment-1518626017

[Ddystopia]

Method run_pending_migrations is also not working:

[aminya]

The find method also doesn't seem to work. rust-analyzer complains that I can't call .execute on the Output of find, while it works with the Rust compiler.

[JasonBoyett]

For some reason my rust analyzer works fine with diesel on my MacBook but I run into issues when I try to use it on pop os.

[opsnull]

I hope the issue can be fixed, it makes me crazy.

[AJTJ]

@weiznich any updates on this? Anywhere I can help?

[Veykril]

This is blocked on the new trait solver integration, there isn't anything we can do right now

[weiznich]

From diesel's point of view there are two QueryDSL methods broken here: filter/find and left_join/inner_join.

At least for the filter/find methods there exists the following workaround:

Instead of this:

let result = users::table.filter(users::id.eq(42)).load::<User>(conn)?;

write this:

let mut user_query = users::table.into_boxed();

user_query = user_query.filter(users::id.eq(42));

let result = user_query.load::<User>(conn)?;

The important parts here are:

• Boxing the query via .into_boxed()
• Storing the boxed query in a variable
• Reassign the variable after applying filter or find

That workarounds the above issue as rust-analyzer is able to infer the type of the boxed query at the first assign. Afterwards it can assume that the type stays the same even if it cannot infer the correct type of the filter/find expression.

I'm not aware of any workaround for the left_join/inner_join methods yet.

I would assume that if someone wants to help resolving both cases for real the best way forward is to build a minimal example that triggers the same behavior. That would mean you would start with the latest diesel version and strip out as much stuff as possible so that the issue still reproduces. See the following blog post for general strategies how to do that.

[realtica]

rust-analyzer version: v0.3.2154 (latest) rustc version: 1.80.1 editor or extension: nvim v0.10

The latest version the inference is ok for tables.., but it returns a let site: {unknown} , and what about the ORM functions like Comment::belonging_to() ? (inference for filter fails)

[weiznich]

I think it might be fine to close this now given that the new trait solver has finally landed in rust-analyzer.

With a "current" version of rust-analyzer (rust-analyzer 0.3.2675-standalone) I get the following result for my test case:

That means rust-analyzer is now able to infer all types correctly :tada:

cc @Veykril @lnicola for the final decision if you want to not close this for specific reasons.

[Veykril]

Yeeeees! 🎉 That is great to hear.

Let's close, if anything pop up again we can just make a new issue