Rollup merge of #132583 - mejrs:tuples, r=compiler-errors

Suggest creating unary tuples when types don't match a trait

When you want to have a variadic function, a common workaround to implement this is to create a trait and then implement that trait for various tuples. For example in `pyo3` there exists
```rust
/// Calls the object with only positional arguments.
pub fn call1(&self, args: impl IntoPy<Py<PyTuple>>) -> PyResult<&PyAny> {
   ...
}
```

with various impls like
```rust
impl<A: IntoPy<PyObject> IntoPy<Py<PyAny>> for (A,)
impl<A: IntoPy<PyObject, B: IntoPy<PyObject> IntoPy<Py<PyAny>> for (A, B)
... etc
```

This means that if you want to call the method with a single item you have to create a unary tuple, like `(x,)`, rather than just `x`.

This PR implements a suggestion to do that, if applicable.

1 files changed, 4 insertions, 0 deletions

diff --git a/tests/ui/layout/rust-call-abi-not-a-tuple-ice-81974.stderr b/tests/ui/layout/rust-call-abi-not-a-tuple-ice-81974.stderr
index cceaddf7803..206a6801065 100644
--- a/tests/ui/layout/rust-call-abi-not-a-tuple-ice-81974.stderr
+++ b/tests/ui/layout/rust-call-abi-not-a-tuple-ice-81974.stderr
@@ -71,6 +71,10 @@ LL |     cachedcoso.call_once(1);
    |
 note: required by a bound in `call_once`
   --> $SRC_DIR/core/src/ops/function.rs:LL:COL
+help: use a unary tuple instead
+   |
+LL |     cachedcoso.call_once((1,));
+   |                          + ++
 
 error: aborting due to 6 previous errors