Anonymous constants should not be included in the Structure View

Environment

• IntelliJ Rust plugin version: 0.3.146.3826-211
• Rust toolchain version: 1.54.0-nightly (bacf770f2 2021-05-05) x86_64-unknown-linux-gnu
• IDE name and version: CLion 2021.1 (CL-211.6693.114)
• Operating system: Linux 5.4.0-72-generic
• Macro expansion engine: new
• Name resolution engine: new

Problem description

Currently anonymous constants (i.e. of the form const _: T = value;) are included in the structure view. This is meaningless: such constants cannot be used in any way and exist solely for compile-time assertions. The static_assertions crate uses them extensively, and a module with many assertions will be polluted by many meaningless constant definitions.

Steps to reproduce

Add static_assertions crate to the dependencies. In any module write

static_assertions::const_assert_eq!(0, 1 - 1);

The structure view gets a new entry of the form null: [{}; {}]. These nameless entries should not be added.

The reason the nameless constant is added is that the above macro expands to the following code:

#[allow(unknown_lints, eq_op)]
    const _: [(); 0 - !{
        const ASSERT: bool = (0 == (1 - 1));
        ASSERT
    } as usize] = [];

which statically checks the equality of terms in the macro.

Similar anonymous constants are added for most other macros in static_assertions, such as assert_eq_size, assert_impl_one or assert_obj_safe.