Nonsensical suggested type using chumsky select! (E0284)

[schrottkatze]

Code

https://forge.katzen.cafe/schrottkatze/iowo/src/commit/bfd4b3765f35a98112b691d2f29c2c3446fe4d5c/crates/lang/src/parser.rs#L41-L44

Current output

error[E0284]: type annotations needed for `Select<{closure@/home/jade/.cargo/registry/src/index.crates.io-6f17d22bba15001f/chumsky-1.0.0-alpha.6/src/lib.rs:2782:13: 2782:28}, I, Expression<'_>, E>`
  --> crates/lang/src/parser.rs:41:13
   |
41 |         let lit = select! {
   |             ^^^
42 |             Token::Int(i) = e => Expression::new(Expr::Lit(ast::Lit::Int(i.parse().unwrap())), e.span()),
   |                                                                                                  ---- type must be known at this point
   |
   = note: cannot satisfy `<_ as chumsky::input::Input<'_>>::Span == SimpleSpan`
help: consider giving `lit` an explicit type, where the type for type parameter `I` is specified
   |
41 |         let lit: Select<{closure@/home/jade/.cargo/registry/src/index.crates.io-6f17d22bba15001f/chumsky-1.0.0-alpha.6/src/lib.rs:2782:13: 2782:28}, I, Expression<'_>, E> = select! {
   |                +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Desired output

No response

Rationale and extra context

This error is very confusing and unreadable, and the compiler even proposes adding a type containing a local path into the code.

That seems very problematic and incorrect.

Other cases

No response

Rust Version

rustc 1.77.0-nightly (190f4c961 2024-01-09)
binary: rustc
commit-hash: 190f4c96116a3b59b7de4881cfec544be0246d84
commit-date: 2024-01-09
host: x86_64-unknown-linux-gnu
release: 1.77.0-nightly
LLVM version: 17.0.6

Anything else?

No response

[compiler-errors]

Try updating your nightly compiler and checking if it's still like that? You're using a nightly compiler from January.

[estebank]

To second compiler-errors' comment, I know that there was a change in this suggestion sometime in the past month.

Edit: nevermind

rust/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

Lines 226 to 227 in b376f49

	// FIXME: The same thing for closures, but this only works when the closure
	// does not capture anything.

[estebank]

Output with the PR linked above:

error[E0284]: type annotations needed for `Select<{closure@lib.rs:2782:13}, _, Expression<'_>, _>`
  --> crates/lang/src/parser.rs:41:13
   |
41 |         let lit = select! {
   |             ^^^
42 |             Token::Int(i) = e => Expression::new(Expr::Lit(ast::Lit::Int(i.parse().unwrap())), e.span()),
   |                                                                                                  ---- type must be known at this point
   |
   = note: the full type name has been written to '/home/gh-estebank/iowo/target/debug/deps/lang-e2d6e25819442273.long-type-4587393693885174369.txt'
   = note: cannot satisfy `<_ as chumsky::input::Input<'_>>::Span == SimpleSpan`
help: consider giving `lit` an explicit type, where the type for type parameter `I` is specified
   |
41 |         let lit: Select<for<'a, 'b> fn(tokens::Token<'_>, &'a mut MapExtra<'_, 'b, _, _>) -> Option<Expression<'_>>, _, Expression<'_>, _> = select! {
   |                +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

We still need a minimal repro to add a test to the test suite.

[estebank]

Needs test.

[pacak]

Minimized reproduction in 1.77 nightly

struct Select<F, I>(F, I);

fn select<F, I>(filter: F) -> Select<F, I> {

}

fn parser1() {
    let lit = select(|x| match x {
        _ => (),
    });
}

% rustc --version
rustc 1.77.0-nightly (ca663b06c 2024-01-08)

error[E0308]: mismatched types
 --> src/lib.rs:3:31
  |
3 | fn select<F, I>(filter: F) -> Select<F, I> {
  |    ------                     ^^^^^^^^^^^^ expected `Select<F, I>`, found `()`
  |    |
  |    implicitly returns `()` as its body has no tail or `return` expression
  |
  = note: expected struct `Select<F, I>`
          found unit type `()`

error[E0282]: type annotations needed for `Select<{closure@src/lib.rs:8:22: 8:25}, I>`
 --> src/lib.rs:8:9
  |
8 |     let lit = select(|x| match x {
  |         ^^^
  |
help: consider giving `lit` an explicit type, where the type for type parameter `I` is specified
  |
8 |     let lit: Select<{closure@src/lib.rs:8:22: 8:25}, I> = select(|x| match x {
  |            ++++++++++++++++++++++++++++++++++++++++++++

Some errors have detailed explanations: E0282, E0308.
For more information about an error, try `rustc --explain E0282`.