Auto merge of rust-lang#11756 - y21:issue11755, r=Manishearth

[`unused_enumerate_index`]: don't ICE on empty tuples

Fixes rust-lang#11755

changelog: [`unused_enumerate_index`]: don't ICE on empty tuples

I'm going to nominate for beta backport because the code that is needed to trigger this seems likely to occur in real code
`@rustbot` label +beta-nominated

src/tools/clippy/clippy_lints/src/loops/unused_enumerate_index.rs

@@ -9,7 +9,7 @@ use rustc_middle::ty;
 
 /// Checks for the `UNUSED_ENUMERATE_INDEX` lint.
 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, arg: &'tcx Expr<'_>, body: &'tcx Expr<'_>) {
-    let PatKind::Tuple(tuple, _) = pat.kind else {
+    let PatKind::Tuple([index, elem], _) = pat.kind else {
         return;
     };
 
@@ -19,7 +19,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, arg: &'tcx
 
     let ty = cx.typeck_results().expr_ty(arg);
 
-    if !pat_is_wild(cx, &tuple[0].kind, body) {
+    if !pat_is_wild(cx, &index.kind, body) {
         return;
     }
 
@@ -53,7 +53,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, arg: &'tcx
                 diag,
                 "remove the `.enumerate()` call",
                 vec![
-                    (pat.span, snippet(cx, tuple[1].span, "..").into_owned()),
+                    (pat.span, snippet(cx, elem.span, "..").into_owned()),
                     (arg.span, base_iter.to_string()),
                 ],
             );

src/tools/clippy/tests/ui/crashes/ice-11755.rs

@@ -0,0 +1,5 @@
+#![warn(clippy::unused_enumerate_index)]
+
+fn main() {
+    for () in [()].iter() {}
+}