Do not ICE when dereferencing non-Copy raw pointer

Author: estebank

src/librustc_mir/borrow_check/mod.rs

@@ -1944,14 +1944,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     self.is_mutable(place.as_ref(), is_local_mutation_allowed),
                     self.errors_buffer.is_empty()
                 ) {
-                    // rust-lang/rust#46908: In pure NLL mode this code path should
-                    // be unreachable (and thus we signal an ICE in the else branch here).
-                    span_bug!(
-                        span,
+                    // rust-lang/rust#46908: In pure NLL mode this code path should be
+                    // unreachable, but we use `delay_span_bug` because we can hit this when
+                    // dereferencing a non-Copy raw pointer *and* have `-Ztreat-err-as-bug`
+                    // enabled. We don't want to ICE for that case, as other errors will have
+                    // been emitted (#52262).
+                    self.infcx.tcx.sess.delay_span_bug(span, &format!(
                         "Accessing `{:?}` with the kind `{:?}` shouldn't be possible",
                         place,
                         kind,
-                    );
+                    ));
                 }
                 return false;
             }

src/test/ui/issues/issue-52262.rs

@@ -0,0 +1,25 @@
+// compile-flags:-Ztreat-err-as-bug=5
+#[derive(Debug)]
+enum MyError {
+    NotFound { key: Vec<u8> },
+    Err41,
+}
+
+impl std::error::Error for MyError {}
+
+impl std::fmt::Display for MyError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            MyError::NotFound { key } => write!(
+                f,
+                "unknown error with code {}.",
+                String::from_utf8(*key).unwrap()
+                //~^ ERROR cannot move out of `*key` which is behind a shared reference
+            ),
+            MyError::Err41 => write!(f, "Sit by a lake"),
+        }
+    }
+}
+fn main() {
+    println!("Hello, world!");
+}

src/test/ui/issues/issue-52262.stderr

@@ -0,0 +1,9 @@
+error[E0507]: cannot move out of `*key` which is behind a shared reference
+  --> $DIR/issue-52262.rs:16:35
+   |
+LL |                 String::from_utf8(*key).unwrap()
+   |                                   ^^^^ move occurs because `*key` has type `std::vec::Vec<u8>`, which does not implement the `Copy` trait
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0507`.