insertion failed due to conflict with previously registered route: /*__private__axum_fallback'

[alcroito]

Hi.

Upgrading to latest axum in my project has broken schema generation.

I get the following panic:

hread 'web::routes::tests::generate_open_api_schema' panicked at 'Invalid route "/*__private__axum_fallback": insertion failed due to conflict with previously registered route: /*__private__axum_fallback', /Users/myuser/.cargo/registry/src/index.crates.io-6f17d22bba15001f/aide-0.11.0/src/axum/mod.rs:453:35
stack backtrace:
   0: rust_begin_unwind
             at /rustc/8460ca823e8367a30dda430efda790588b8c84d3/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/8460ca823e8367a30dda430efda790588b8c84d3/library/core/src/panicking.rs:64:14
   2: axum::routing::Router<S,B>::nest
             at /Users/myuser/.cargo/registry/src/index.crates.io-6f17d22bba15001f/axum-0.6.18/src/routing/mod.rs:164:13
   3: aide::axum::ApiRouter<S,B>::nest
             at /Users/myuser/.cargo/registry/src/index.crates.io-6f17d22bba15001f/aide-0.11.0/src/axum/mod.rs:453:23
   4: do_ddns::web::routes::get_pure_router_and_open_api
             at ./src/web/routes.rs:70:24
   5: do_ddns::web::routes::tests::generate_open_api_schema
             at ./src/web/routes.rs:126:24
   6: do_ddns::web::routes::tests::generate_open_api_schema::{{closure}}
             at ./src/web/routes.rs:125:35
   7: core::ops::function::FnOnce::call_once
             at /rustc/8460ca823e8367a30dda430efda790588b8c84d3/library/core/src/ops/function.rs:250:5
   8: core::ops::function::FnOnce::call_once
             at /rustc/8460ca823e8367a30dda430efda790588b8c84d3/library/core/src/ops/function.rs:250:5

Code in question: https://github.com/alcroito/digitalocean-dyndns/blob/master/crates/dyndns/src/web/routes.rs#L70

New axum version: 0.6.18
Previously working one: 0.6.12.

I haven't had time to make a small repro yet, but posting for visibility.

[alcroito]

Ok, made a small repro. Looks like it's not an aide issue, but either an axum issue or how i'm using fallback for nesting under '/'.

use aide::axum::ApiRouter;
use aide::openapi::OpenApi;
use axum::Router;

#[derive(Clone)]
struct SomeState;

async fn serve_static_files() { todo!() }

fn static_router() -> Router<SomeState> {
    Router::new().fallback(serve_static_files)
}

fn make_router() {
    let mut api = OpenApi::default();

    let static_router: ApiRouter<SomeState> = static_router().into();

    let _final_router = ApiRouter::new()
        .nest("/", static_router)
        .finish_api(&mut api);
}

fn main() {
    make_router();
}