fixes panic error index out of bounds in conflicting error

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -456,10 +456,15 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 if let Some(def_id) = def_id
                     && self.infcx.tcx.def_kind(def_id).is_fn_like()
                     && let Some(pos) = args.iter().position(|arg| arg.hir_id == expr.hir_id)
-                    && let ty::Param(_) =
-                        self.infcx.tcx.fn_sig(def_id).skip_binder().skip_binder().inputs()
-                            [pos + offset]
-                            .kind()
+                    && let Some(arg) = self
+                        .infcx
+                        .tcx
+                        .fn_sig(def_id)
+                        .skip_binder()
+                        .skip_binder()
+                        .inputs()
+                        .get(pos + offset)
+                    && let ty::Param(_) = arg.kind()
                 {
                     let place = &self.move_data.move_paths[mpi].place;
                     let ty = place.ty(self.body, self.infcx.tcx).ty;

tests/ui/borrowck/move-error-suggest-clone-panic-issue-127915.rs

@@ -0,0 +1,15 @@
+#![allow(dead_code)]
+
+extern "C" {
+    fn rust_interesting_average(_: i64, ...) -> f64;
+}
+
+fn test<T, U>(a: i64, b: i64, c: i64, d: i64, e: i64, f: T, g: U) -> i64 {
+    unsafe {
+        rust_interesting_average(
+            6, a as f64, b, b as f64, f, c as f64, d, d as f64, e, e as f64, f, g, //~ ERROR use of moved value: `f` [E0382]
+        ) as i64
+    }
+}
+
+fn main() {}

tests/ui/borrowck/move-error-suggest-clone-panic-issue-127915.stderr

@@ -0,0 +1,25 @@
+error[E0382]: use of moved value: `f`
+  --> $DIR/move-error-suggest-clone-panic-issue-127915.rs:10:78
+   |
+LL | fn test<T, U>(a: i64, b: i64, c: i64, d: i64, e: i64, f: T, g: U) -> i64 {
+   |                                                       - move occurs because `f` has type `T`, which does not implement the `Copy` trait
+...
+LL |             6, a as f64, b, b as f64, f, c as f64, d, d as f64, e, e as f64, f, g,
+   |                                       - value moved here                     ^ value used here after move
+   |
+help: if `T` implemented `Clone`, you could clone the value
+  --> $DIR/move-error-suggest-clone-panic-issue-127915.rs:7:9
+   |
+LL | fn test<T, U>(a: i64, b: i64, c: i64, d: i64, e: i64, f: T, g: U) -> i64 {
+   |         ^ consider constraining this type parameter with `Clone`
+...
+LL |             6, a as f64, b, b as f64, f, c as f64, d, d as f64, e, e as f64, f, g,
+   |                                       - you could clone this value
+help: consider restricting type parameter `T`
+   |
+LL | fn test<T: Copy, U>(a: i64, b: i64, c: i64, d: i64, e: i64, f: T, g: U) -> i64 {
+   |          ++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.