Compiler error with Vec<&str> argument: "error: implementation of FromForm is not general enough"

[jakubdabek]

Compiler and crate version:

• nightly-x86_64-unknown-linux-gnu rustc 1.56.0-nightly (30a0a9b69 2021-08-17)
• rocket master#786db9b8

Here's some example code:

use rocket::{get, routes};

#[rocket::main]
async fn main() {
    rocket::build()
        .mount("/", routes![foo_str, foo_string, foo_vec_string, foo_vec_str])
        .launch()
        .await
        .unwrap();
}

#[get("/foo_str?<queries>")]
async fn foo_str(queries: &str) {
    todo!("{:?}", queries)
}
#[get("/foo_string?<queries>")]
async fn foo_string(queries: String) {
    todo!("{:?}", queries)
}
#[get("/foo_vec_string?<queries>")]
async fn foo_vec_string(queries: Vec<String>) {
    todo!("{:?}", queries)
}
#[get("/foo_vec_str?<queries>")]
async fn foo_vec_str(queries: Vec<&str>) {
    todo!("{:?}", queries)
}

The compiler doesn't like this code:

error: implementation of `FromForm` is not general enough
  --> src/bin/main-report.rs:24:1
   |
24 | #[get("/foo_vec_str?<queries>")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FromForm` is not general enough
   |
   = note: `&'0 str` must implement `FromForm<'1>`, for any two lifetimes `'0` and `'1`...
   = note: ...but it actually implements `FromForm<'2>`, for some specific lifetime `'2`
   = note: this error originates in the attribute macro `get` (in Nightly builds, run with -Z macro-backtrace for more info)

Only the last one cannot be compiled, and the error message is maximally unhelpful.

[jakubdabek]

I've tracked the issue down to a rustc issue (rust-lang/rust#69663) and managed to apply a workaround (rust-lang/rust#57478 (comment)) on that example expanded with cargo-expand and compiled manually. I can try to make a PR to change the code generation for the route macros so that the error doesn't show up.