quickfix inserts where clause for tuple structs in wrong place and causes errors · Issue #10923 · rust-lang/rust-analyzer (original) (raw)

I am newbie, so i will repeat when i learnt on rust official discord while debugging this issue.
Reproduce error:

1. add derive_more and halfbrown as dependencies.
2. create a tuple struct with halfbrown::HashMap as its only field.
3. derive IntoIterator using derive_more with the #[derive(IntoIterator)]
4. vscode/RA complain that the macro needs trait bounds of IntoIterator for the inner field.
5. suggest the quickfix to put a where class specifying the requirement. I click on quickfix
   
6. quickfix introduces the where clause between the struct name and the parenthesis which declare the fields, which introduces a whole new class of errors
   

the full errors that cargo check gives me:

error: proc-macro derive panicked
 --> src/main.rs:7:10
  |
7 | #[derive(IntoIterator)]
  |          ^^^^^^^^^^^^
  |
  = help: message: derive(IntoIterator) only works when forwarding to a single field. Try putting #[into_iterator] or #[into_iterator(ignore)] on the fields in the struct

error[E0658]: parenthetical notation is only stable when used with `Fn`-family traits
 --> src/main.rs:8:72
  |
8 | pub struct UOMap<K: std::hash::Hash,V> where halfbrown::HashMap<K, V>: std::iter::IntoIterator(HashMap<K, V>);
  |                                                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #29625 <https://github.com/rust-lang/rust/issues/29625> for more information

error[E0107]: this trait takes 0 generic arguments but 1 generic argument was supplied
   --> src/main.rs:8:83
    |
8   | pub struct UOMap<K: std::hash::Hash,V> where halfbrown::HashMap<K, V>: std::iter::IntoIterator(HashMap<K, V>);
    |                                                                                   ^^^^^^^^^^^^--------------- help: remove these parenthetical generics
    |                                                                                   |
    |                                                                                   expected 0 generic arguments
    |
note: trait defined here, with 0 generic parameters
   --> /home/red/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/collect.rs:204:11
    |
204 | pub trait IntoIterator {
    |           ^^^^^^^^^^^^

error[E0220]: associated type `Output` not found for `IntoIterator`
 --> src/main.rs:8:83
  |
8 | pub struct UOMap<K: std::hash::Hash,V> where halfbrown::HashMap<K, V>: std::iter::IntoIterator(HashMap<K, V>);
  |                                                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ associated type `Output` not found

Some errors have detailed explanations: E0107, E0220, E0658.
For more information about an error, try `rustc --explain E0107`.

The Fix:
changing
pub struct UOMap<K: std::hash::Hash,V> where halfbrown::HashMap<K, V>: std::iter::IntoIterator(HashMap<K, V>);
to
pub struct UOMap<K: std::hash::Hash,V>(HashMap<K, V>) where halfbrown::HashMap<K, V>: std::iter::IntoIterator;
basically, insert the where clause AFTER the closing parenthesis. from what i was told on the discord, where clause needs to come just before the first {, but idk how it will be dealt with in regards to tuple struct.

rust-analyzer version: rust-analyzer version: d9b2291 2021-11-29 stable

rustc version: rustc 1.57.0 (f1edd0429 2021-11-29)