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1// Regression test for #67037.
2//
3// In type checking patterns, E0023 occurs when the tuple pattern and the expected
4// tuple pattern have different number of fields. For example, as below, `P()`,
5// the tuple struct pattern, has 0 fields, but requires 1 field.
6//
7// In emitting E0023, we try to see if this is a case of e.g., `Some(a, b, c)` but where
8// the scrutinee was of type `Some((a, b, c))`, and suggest that parenthesis be added.
9//
10// However, we did not account for the expected type being different than the tuple pattern type.
11// This caused an issue when the tuple pattern type (`P<T>`) was generic.
12// Specifically, we tried deriving the 0th field's type using the `substs` of the expected type.
13// When attempting to substitute `T`, there was no such substitution, so "out of range" occured.
14
15struct U {} // 0 type parameters offered
16struct P<T>(T); // 1 type parameter wanted
17
18fn main() {
19 let P() = U {}; //~ ERROR mismatched types
20 //~^ ERROR this pattern has 0 fields, but the corresponding tuple struct has 1 field
21}