Methods provided via Deref<Target> are not being found

[woody77]

rust-analyzer version: (eg. output of "rust-analyzer: Show RA Version" command, accessible in VSCode via Ctrl/⌘+Shift+P)

rustc version: rust-analyzer version: 0.4.1202-standalone rustc 1.65.0-nightly (350cca3b6 2022-08-30)

relevant settings: VSCode remote, with a very large project (1000s of crates), no extra env settings for CHALK

Methods from OtherType that are defined for a type (ThisType) via implementing Deref<Target=OtherType> are not being found as valid symbols, and flagged as unresolvedReference.

Using the following struct:

struct Wrapper(pub String);

impl std::ops::Deref for Wrapper {
    type Target = str;

    fn deref(&self) -> &Self::Target {
        self.0.as_str()
    }
}

The following do not resolve .chars():

But the following do resolve chars() correctly:

Full source (and proof that these work) at: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=d5c1d59fa47c1228df2be80042ec41a1

[woody77]

This used to work for us, and now we've been seeing this for the last few weeks at least.

[woody77]

And to use all types from the same file: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1778880d91ecbeae9ee16cfd7c77e613

impl Wrapper {
    fn print_self(&self) {
        println!("{}", self.0);
    }
}

struct OtherWrapper(pub Wrapper);

impl std::ops::Deref for OtherWrapper {
    type Target=Wrapper;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

Using the methods from the Deref<Target=Wrapper> impl for OtherWrapper aren't resolved:

[Veykril]

So this only happens in this big project of yours?

[woody77]

It's where I see it. It's both:

• rust-project.json
• 1000s of crates

We've had some issues in the past where we needed to do things like increase chalk's overflow limits to stop things from breaking. I don't have a good sense of how to go about seeing if that's an issue (turning on any logging at all becomes a massive flood due to the number of crates involved).

If you give some guidance on what tracing to turn on, I can see if this is something like chalk giving up on the resolution of the types.

[tbodt]

Bisected to 2c2520fbb48b977a805b46af79e4016a4394e719

[woody77]

Which is the sysroot support for project_json workspaces PR: https://github.com/rust-lang/rust-analyzer/pull/12858

[tbodt]

On further investigation, this has nothing to do with Deref. The problem can be seen with just this:

trait Foo {
    type Bar;
    fn foo(&self) -> Bar;
}

impl Foo for () {
    type Bar = i32;
    fn foo(&self) -> Bar { 0 }
}

fn foo() {
    let _a = ().foo();
}

rust-analyzer can't infer the type of _a. Changing Bar to be a trait type parameter instead of an associated type fixes it. So the bug is something to do with associated types.

edit: this was a red herring, the actual problem was me not realizing I needed to write Self::Bar and not just Bar

[kangalio]

:+1: This issue comes up quite often for me due to many useful methods being implemented on the Deref type.

• Vec: .iter(), .len(), .get(), .first()
• String: .parse(), .split(), .trim().

Most notably, those unrecognized methods break autocomplete, Go To Definition and type inference.

[flodiebold]

@kangalioo are you working in the same project as @woody77, or a similar large project using rust-project.json?

[woody77]

While @tbodt did run down a red-herring, while talking with him about it Friday I confirmed that specifying a sysroot in rust-project.json causes RA to inject the sysroot crates: https://github.com/rust-lang/rust-analyzer/blob/8ee23f4f0aebf344089bfc201f1dbf641534cf94/crates/project-model/src/workspace.rs#L399

This changed in: https://github.com/rust-lang/rust-analyzer/pull/12858/files#diff-53e4b6b2c1ff2465d8abd50db160753199426fd788ddcad925752e0838e28de2R233

Before, if rust-project.json specified a sysroot_src that would be used to load the sysroots. As of that change, specifying a sysroot causes the sysroot_src to be inferred, and then ProjectWorkspace::to_roots() will find a sysroot (actually a sysroot_src), and then inject the sysroot packages.

And now there are two sets of sysroot packages found in the deps of every crate, it seems?

How to best model this for RA in a cross-compiling, multi-architecture build like we (Fuchsia) have is unclear. RA today doesn't handle different configurations of crates, but we compile many for both host and target (often both different in OS and Arch: linux.x64 and mac.x64/aarch64 vs. fuchsia.arm64 or fuchsia.x64).

I can remove the code that adds the sysroot crates (from the class in GN that produces our rust-project.json file), although I'll have to think about how to locate the sysroot if they're not directly in the crate graph that it's generating.

[Veykril]

Before, if rust-project.json specified a sysroot_src that would be used to load the sysroots. As of that change, specifying a sysroot causes the sysroot_src to be inferred, and then ProjectWorkspace::to_roots() will find a sysroot (actually a sysroot_src), and then inject the sysroot packages.

I am a bit confused, are you saying you are no longer specifying the sysroot_src as you did before? If you have the sysroot_src specified then behavior shouldn't really have changed for you here, no matter if you also specified the sysroot or not now from what I can tell?

[woody77]

No, we've never specified sysroot_src. That was added after we added our rust-project.json emitter to GN, and were already adding the sysroot crates as part of rust-project.json (as was required at the time).

When we started specifying sysroot, it started to infer what the sysroot_src would have been, and RA started adding the sysroot crates to the list of roots, even though we've already included them.

This happens at: https://github.com/rust-lang/rust-analyzer/blob/53b6d69e931a52cca44ef94c3b713b4d255754b8/crates/project-model/src/workspace.rs#L269-L274

[Veykril]

Hmm, so why are you now specifying sysroot when you are still managing the crates manually for it?

[woody77]

We’re now specifying the sysroot because of the proc_macro_srv. That’s the only reason we added it.

On Tue, Oct 25, 2022 at 4:49 AM Lukas Wirth @.***> wrote:

Hmm, so why are you now specifying sysroot when you are still managing the crates manually for it?

— Reply to this email directly, view it on GitHub https://github.com/rust-lang/rust-analyzer/issues/13238#issuecomment-1290421927, or unsubscribe https://github.com/notifications/unsubscribe-auth/AEFLWQCQXH6UJYZOPLQLJATWE7CKZANCNFSM6AAAAAAQN3SJHY . You are receiving this because you were mentioned.Message ID: @.***>

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[Veykril]

Right, unfortunately the way things are written atm we either expect a sysroot fully or we expect none. Changing things is a bit more involved and I'd need to do some digging to see if there is a feasible way to change stuff to not error out when certain parts are missing (by choice). Nevertheless it would be probably beneficial for you to look into supporting the sysroot via the correct fields instead of adding them manually if possible.

[woody77]

I'm also (in my "spare time") looking at seeing what the impact is of not including the sysroot crates in our generated rust-project.json file. The only concern I have is the proc_macro crate, which we add to proc macros, and I haven't found if RA adds that for implicitly as well.

[Veykril]

r-a should add the proc-macro crate to everything as a dependency (because every crate type, even non proc-macro ones have it as a dependency in rust)

[woody77]

I've got a PR up for our rust-project.json generation, which removes the explicit addition of the sysroot crates, and lets rust-analyzer infer it from the sysroot field.

[woody77]

The CL has landed, and our next GN roll should pick it up and fix this for our developers. Thanks for all the debugging help!

[zhiqiangxu]

It seems this issue still exists occasionally at least for rust-analyzer version: 0.3.1498-standalone (3a27518fe 2023-04-30).

[flodiebold]

@zhiqiangxu probably not the same issue.