impl Trait in macros: subst.rs "index out of bounds: the len is 1 but the index is 1"

[SkiFire13]

#9639 has been closed, however a very similar issue is still happening to me. I encountered it the moment I added a ctor! macro call at this line. (Note that the linked crate requires beta/nightly to compile, but only due to code unrelated to the issue; the minimal repro compiles fine on stable.)
The macro call looks required for the crash to trigger, and manually expanding it solves the issue. This also happened in #9639 and the minimal repro posted there doesn't seem to address this.

Here's a minimal repro of my issue:

macro_rules! ty {
    () => {
        impl Sized
    }
}

fn foo(_: ty!()) {}

fn bar() {
    foo(());
}

It gives this error in vscode's output tab:

Panic context:
> 
version: 516eb40ba 2021-09-13 stable
request: rust-analyzer/inlayHints InlayHintsParams {
    text_document: TextDocumentIdentifier {
        uri: Url {
            scheme: "file",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: None,
            port: None,
            path: "/g%3A/WorkSpace/repro/src/lib.rs",
            query: None,
            fragment: None,
        },
    },
}

thread '<unnamed>' panicked at 'index out of bounds: the len is 0 but the index is 0', C:\Users\runneradmin\.cargo\registry\src\gb.xjqchip.workers.dev-1ecc6299db9ec823\chalk-ir-0.71.0\src\fold\subst.rs:58:19
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Panic context:
> 
version: 516eb40ba 2021-09-13 stable
request: rust-analyzer/inlayHints InlayHintsParams {
    text_document: TextDocumentIdentifier {
        uri: Url {
            scheme: "file",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: None,
            port: None,
            path: "/g%3A/WorkSpace/repro/src/lib.rs",
            query: None,
            fragment: None,
        },
    },
}

thread '<unnamed>' panicked at 'index out of bounds: the len is 0 but the index is 0', C:\Users\runneradmin\.cargo\registry\src\gb.xjqchip.workers.dev-1ecc6299db9ec823\chalk-ir-0.71.0\src\fold\subst.rs:58:19
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Panic context:
> 
version: 516eb40ba 2021-09-13 stable
request: rust-analyzer/inlayHints InlayHintsParams {
    text_document: TextDocumentIdentifier {
        uri: Url {
            scheme: "file",
            cannot_be_a_base: false,
            username: "",
            password: None,
            host: None,
            port: None,
            path: "/g%3A/WorkSpace/repro/src/lib.rs",
            query: None,
            fragment: None,
        },
    },
}

thread '<unnamed>' panicked at 'index out of bounds: the len is 0 but the index is 0', C:\Users\runneradmin\.cargo\registry\src\gb.xjqchip.workers.dev-1ecc6299db9ec823\chalk-ir-0.71.0\src\fold\subst.rs:58:19
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

I can't seem to get a full backtrace even when setting RUST_BACKTRACE=full.

[flodiebold]

If that's really everything needed to trigger it, it should be pretty straightforward to turn it into a test in hir_ty/src/tests/regression.rs (the only thing to keep in mind is to add //- minicore: sized).

[SkiFire13]

it should be pretty straightforward to turn it into a test

Maybe I was too quick to go to the details, but this is still happening in rust-analyzer 516eb40ba 2021-09-13 stable and b73b32147 2021-09-18 dev. It's not a case fixed together with #9639, it's a really similar issue that's still present.

the only thing to keep in mind is to add //- minicore: sized

If that's due to the Sized trait, it's not required, any trait works (even non defined ones).

[SkiFire13]

Update: I've looked around trying to understand what's going on, and looks like the problem seems to be that hir_def::generics::GenericParams::fill_implicit_impl_trait_args ignores TypeRef::Macro. This is however wrong is case the macro expands to an impl Trait, like in my example. However expanding macros at this stage doesn't seem to be supported, so I'm kinda lost on what to do.