Do not emit E0277 on incorrect tuple destructured binding

src/test/ui/elide-errors-on-mismatched-tuple.rs

@@ -0,0 +1,28 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Hide irrelevant E0277 errors (#50333)
+
+trait T {}
+
+struct A;
+impl T for A {}
+impl A {
+    fn new() -> Self {
+        Self {}
+    }
+}
+
+fn main() {
+    let (a, b, c) = (A::new(), A::new()); // This tuple is 2 elements, should be three
+    //~^ ERROR mismatched types
+    let ts: Vec<&T> = vec![&a, &b, &c];
+    // There is no E0277 error above, as `a`, `b` and `c` are `TyErr`
+}

src/test/ui/elide-errors-on-mismatched-tuple.stderr

@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> $DIR/elide-errors-on-mismatched-tuple.rs:24:9
+   |
+LL |     let (a, b, c) = (A::new(), A::new()); // This tuple is 2 elements, should be three
+   |         ^^^^^^^^^ expected a tuple with 2 elements, found one with 3 elements
+   |
+   = note: expected type `(A, A)`
+              found type `(_, _, _)`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.