Failed compilation of the rust project with a custom structure and the use of macros

I'm starting to learn rust and playing with the structure of the project. Now I have such a project structure :

project
└─── src
│   └─── core
│   │   └─── lib.rs
│   │   └─── Cargo.toml
│   └─── api
│       └─── main.rs
│       └─── Cargo.toml
└─── Cargo.toml

The contents of the toml files are as follows:
project/Cargo.toml

[workspace]
members = [ 
    "src/core", 
    "src/api"
]

project/src/api/Cargo.toml

[package]
name = "api"
version = "0.1.0"

[[bin]]
name = "api"
path = "main.rs"

[dependencies]
core = { path = "../core" }
rocket =  { version = "0.5.0", features = ["json"] } 

With these settings, the project is not compiled if in main.rs I'm trying to work with rocket macros. main.rs (the code is taken from the description of the rocket package):

#[macro_use] extern crate rocket;

#[get("/<name>/<age>")]
fn hello(name: &str, age: u8) -> String {
    format!("Hello, {} year old named {}!", age, name)
}

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/hello", routes![hello])
}

I get an error:

error: macro-expanded `macro_export` macros from the current crate cannot be referred to by absolute paths
 --> src\api\main.rs:4:4
  |
4 | fn hello(name: &str, age: u8) -> String {
  |    ^^^^^
  |
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #52234 <https://github.com/rust-lang/rust/issues/52234>     
note: the macro is defined here
 --> src\api\main.rs:3:1
  |
3 | #[get("/<name>/<age>")]
  | ^^^^^^^^^^^^^^^^^^^^^^^
  = note: `#[deny(macro_expanded_macro_exports_accessed_by_absolute_paths)]` on by default
  = note: this error originates in the attribute macro `get` (in Nightly builds, run with -Z macro-backtrace for more info)

error: could not compile `api` (bin "api") due to 1 previous error

What is the reason for this and how can it be fixed?

But

I tried to create an api project with the src folder, this problem does not repeat.

api
└─── src
│   └─── main.rs
└─── Cargo.toml

But I don't want to keep the src folders for each project (main and lib) because workspace already has src. What can be done about it?

Looks like the Rocket docs haven't been updated in a while because the #[macro_use] syntax was phased out in Rust 1.30. Simply import these macros via the use declaration like so:

use rocket::{get, launch, routes};

#[get("/<name>/<age>")]
fn hello(name: &str, age: u8) -> String {
    format!("Hello, {} year old named {}!", age, name)
}

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/hello", routes![hello])
}

This code compiles.