Avoid ICE when adjusting bad self ty

Author: estebank

src/librustc_typeck/check/method/confirm.rs

@@ -141,14 +141,24 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
     ///////////////////////////////////////////////////////////////////////////
     // ADJUSTMENTS
 
-    fn adjust_self_ty(&mut self,
-                      unadjusted_self_ty: Ty<'tcx>,
-                      pick: &probe::Pick<'tcx>)
-                      -> Ty<'tcx> {
+    fn adjust_self_ty(
+        &mut self,
+        unadjusted_self_ty: Ty<'tcx>,
+        pick: &probe::Pick<'tcx>,
+    ) -> Ty<'tcx> {
         // Commit the autoderefs by calling `autoderef` again, but this
         // time writing the results into the various tables.
         let mut autoderef = self.autoderef(self.span, unadjusted_self_ty);
-        let (_, n) = autoderef.nth(pick.autoderefs).unwrap();
+        let (_, n) = match autoderef.nth(pick.autoderefs) {
+            Some(n) => n,
+            None => {
+                self.tcx.sess.delay_span_bug(
+                    syntax_pos::DUMMY_SP,
+                    &format!("failed autoderef {}", pick.autoderefs),
+                );
+                return self.tcx.types.err;
+            }
+        };
         assert_eq!(n, pick.autoderefs);
 
         let mut adjustments = autoderef.adjust_steps(self, Needs::None);

src/test/ui/issues/issue-65611.rs

@@ -0,0 +1,63 @@
+use std::mem::MaybeUninit;
+use std::ops::Deref;
+
+pub unsafe trait Array {
+    /// The array’s element type
+    type Item;
+    #[doc(hidden)]
+    /// The smallest index type that indexes the array.
+    type Index: Index;
+    #[doc(hidden)]
+    fn as_ptr(&self) -> *const Self::Item;
+    #[doc(hidden)]
+    fn as_mut_ptr(&mut self) -> *mut Self::Item;
+    #[doc(hidden)]
+    fn capacity() -> usize;
+}
+
+pub trait Index : PartialEq + Copy {
+    fn to_usize(self) -> usize;
+    fn from(usize) -> Self;
+}
+
+impl Index for usize {
+    fn to_usize(self) -> usize { self }
+    fn from(val: usize) -> Self {
+        val
+    }
+}
+
+unsafe impl<T> Array for [T; 1] {
+    type Item = T;
+    type Index = usize;
+    fn as_ptr(&self) -> *const T { self as *const _ as *const _ }
+    fn as_mut_ptr(&mut self) -> *mut T { self as *mut _ as *mut _}
+    fn capacity() -> usize { 1 }
+}
+
+impl<A: Array> Deref for ArrayVec<A> {
+    type Target = [A::Item];
+    #[inline]
+    fn deref(&self) -> &[A::Item] {
+        panic!()
+    }
+}
+
+pub struct ArrayVec<A: Array> {
+    xs: MaybeUninit<A>,
+    len: usize,
+}
+
+impl<A: Array> ArrayVec<A> {
+    pub fn new() -> ArrayVec<A> {
+        panic!()
+    }
+}
+
+fn main() {
+    let mut buffer = ArrayVec::new();
+    let x = buffer.last().unwrap().0.clone();
+    //~^ ERROR type annotations needed
+    //~| ERROR no field `0` on type `&_`
+    buffer.reverse();
+}

src/test/ui/issues/issue-65611.stderr

@@ -0,0 +1,18 @@
+error[E0282]: type annotations needed
+  --> $DIR/issue-65611.rs:59:20
+   |
+LL |     let x = buffer.last().unwrap().0.clone();
+   |                    ^^^^ cannot infer type for `T`
+   |
+   = note: type must be known at this point
+
+error[E0609]: no field `0` on type `&_`
+  --> $DIR/issue-65611.rs:59:36
+   |
+LL |     let x = buffer.last().unwrap().0.clone();
+   |                                    ^
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0282, E0609.
+For more information about an error, try `rustc --explain E0282`.