Add a regression test for #123630

compiler should not suggest nonsensical signatures, original suggestion was

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`.

0 files changed, 0 insertions, 0 deletions