ices/72911.rs: fixed with errors

[github-actions]

Issue: rust-lang/rust#72911

pub struct Lint {}

impl Lint {}

/// Gathers all files in `src/clippy_lints` and gathers all lints inside
pub fn gather_all() -> impl Iterator<Item = Lint> {
    lint_files().flat_map(|f| gather_from_file(&f))
}

fn gather_from_file(dir_entry: &walkdir::DirEntry) -> impl Iterator<Item = Lint> {
    unimplemented!()
}

/// Collects all .rs files in the `clippy_lints/src` directory
fn lint_files() -> impl Iterator<Item = walkdir::DirEntry> {
    unimplemented!()
}

pub fn main() {}

=== stdout ===
=== stderr ===
error[E0433]: failed to resolve: use of undeclared type or module `walkdir`
  --> /home/runner/work/glacier/glacier/ices/72911.rs:10:33
   |
10 | fn gather_from_file(dir_entry: &walkdir::DirEntry) -> impl Iterator<Item = Lint> {
   |                                 ^^^^^^^ use of undeclared type or module `walkdir`

error[E0433]: failed to resolve: use of undeclared type or module `walkdir`
  --> /home/runner/work/glacier/glacier/ices/72911.rs:15:41
   |
15 | fn lint_files() -> impl Iterator<Item = walkdir::DirEntry> {
   |                                         ^^^^^^^ use of undeclared type or module `walkdir`

error[E0720]: cannot resolve opaque type
  --> /home/runner/work/glacier/glacier/ices/72911.rs:6:24
   |
6  | pub fn gather_all() -> impl Iterator<Item = Lint> {
   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^ recursive opaque type
7  |     lint_files().flat_map(|f| gather_from_file(&f))
   |     -----------------------------------------------
   |     |
   |     returning here with type `std::iter::FlatMap<impl std::iter::Iterator, [type error], [closure@/home/runner/work/glacier/glacier/ices/72911.rs:7:27: 7:51]>`
   |     returning here with type `std::iter::FlatMap<impl std::iter::Iterator, [type error], [closure@/home/runner/work/glacier/glacier/ices/72911.rs:7:27: 7:51]>`
...
10 | fn gather_from_file(dir_entry: &walkdir::DirEntry) -> impl Iterator<Item = Lint> {
   |                                                       -------------------------- returning this opaque type `std::iter::FlatMap<impl std::iter::Iterator, [type error], [closure@/home/runner/work/glacier/glacier/ices/72911.rs:7:27: 7:51]>`
...
15 | fn lint_files() -> impl Iterator<Item = walkdir::DirEntry> {
   |                    --------------------------------------- returning this opaque type `std::iter::FlatMap<impl std::iter::Iterator, [type error], [closure@/home/runner/work/glacier/glacier/ices/72911.rs:7:27: 7:51]>`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0433, E0720.
For more information about an error, try `rustc --explain E0433`.
==============

[JohnTitor]

The ICE no longer happens.