rust-analyzer shows false positive E0308 type mismatch errors with PyO3 macros

[bigg-S]

Description

rust-analyzer shows false positive E0308 type mismatch errors when using PyO3's #[pyclass] macro in combination with third-party procedural macros (specifically pyo3_stub_gen_derive::gen_stub_pyclass). The errors appear as:

expected &'static [fn() -> TypeInfo], found &[fn() -> TypeInfo; 0]
expected &'static [MemberInfo], found &[MemberInfo; 0]
expected &'static [PyType_Slot], found &[PyType_Slot; 0]
expected &'static [MaybeRuntimePyMethodDef], found &[MaybeRuntimePyMethodDef; 0]

Despite these rust-analyzer errors, the code compiles and runs perfectly.

Steps to Reproduce

1. Create a PyO3 project with the following dependencies:

[dependencies]
pyo3 = { version = "*" }
pyo3-polars = { version = "0.22.0", features = ["derive", "dtype-full", "lazy"] }
pyo3-stub-gen = { version = "0.10.0", default-features = false }

2. Create a struct with both PyO3 and stub generation macros:

use pyo3::prelude::*;
use pyo3_stub_gen::derive::{gen_stub_pyclass, gen_stub_pymethods};

#[gen_stub_pyclass]
#[pyclass]
#[derive(Clone)]
pub struct YourStruct;

#[gen_stub_pymethods]
#[pymethods]
impl YourStruct {
    #[staticmethod]
    fn example_method() -> PyResult<f64> {
        Ok(42.0)
    }
}

3. Open the project in VS Code with rust-analyzer extension
4. Observe the E0308 errors in rust-analyzer, while cargo check passes without issues

Expected Behavior

rust-analyzer should not show type mismatch errors for properly written PyO3 code that compiles successfully.

Actual Behavior

rust-analyzer shows multiple E0308 type mismatch errors related to array-to-slice coercion in macro-generated code.

Environment

• Rust version: 1.89.0 (nightly)
• rust-analyzer version: v0.3.2509
• Operating System: macOS
• Python version: 3.13
• Cargo.toml setup:

  pyo3 = { version = "*" }
  pyo3-polars = { version = "0.22.0", features = ["derive", "dtype-full", "lazy"] }
  pyo3-stub-gen = { version = "0.10.0", default-features = false }

Additional Context

• The issue appears to be related to how rust-analyzer handles procedural macro expansion when multiple proc macros are combined
• The code works perfectly at runtime and passes all cargo commands
• This affects developer experience as it creates noise in the IDE with false error indicators

Workaround

Currently, disabling E0308 diagnostics in rust-analyzer settings as a workaround.

[Distortedlogic]

I believe there is a regression in one of the latest nightly versions .. downgrading to a few days ago resolves .. I seen this 'static type error as well as a slice vs sized slice [u8] vs [u8; 5] in marco expansions with the nightly that has the regression