Fix rebase issue and test

Author: fanzier

compiler/rustc_typeck/src/check/fn_ctxt/checks.rs

@@ -17,6 +17,7 @@ use rustc_hir::{ExprKind, Node, QPath};
 use rustc_middle::ty::adjustment::AllowTwoPhase;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::{self, Ty};
+use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{self, MultiSpan, Span};
@@ -515,6 +516,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     /// Type check a `let` statement.
     pub fn check_decl_local(&self, local: &'tcx hir::Local<'tcx>) {
+        // Check for destructuring assignment.
+        match local.source {
+            hir::LocalSource::AssignDesugar(eq_sign_span)
+                if !self.tcx.features().destructuring_assignment =>
+            {
+                feature_err(
+                    &self.tcx.sess.parse_sess,
+                    sym::destructuring_assignment,
+                    eq_sign_span,
+                    "destructuring assignments are unstable",
+                )
+                .span_label(local.pat.span, "cannot assign to this expression")
+                .emit();
+            }
+            _ => {}
+        }
+
         // Determine and write the type which we'll check the pattern against.
         let ty = self.local_ty(local.span, local.hir_id).decl_ty;
         self.write_ty(local.hir_id, ty);

src/test/ui/destructuring-assignment/struct_destructure_fail.stderr

@@ -29,6 +29,15 @@ error[E0027]: pattern does not mention field `b`
    |
 LL |     Struct { a, _ } = Struct { a: 1, b: 2 };
    |     ^^^^^^^^^^^^^^^ missing field `b`
+   |
+help: include the missing field in the pattern
+   |
+LL |     Struct { a, b, _ } = Struct { a: 1, b: 2 };
+   |               ^^^
+help: if you don't care about this missing field, you can explicitely ignore it
+   |
+LL |     Struct { a, .., _ } = Struct { a: 1, b: 2 };
+   |               ^^^^
 
 error: aborting due to 5 previous errors
 

src/test/ui/suggestions/if-let-typo.stderr

@@ -43,15 +43,6 @@ error[E0308]: mismatched types
 LL |     if Some(foo) = bar {}
    |        ^^^^^^^^^^^^^^^ expected `bool`, found `()`
 
-error[E0308]: mismatched types
-  --> $DIR/if-let-typo.rs:9:12
-   |
-LL |     if 3 = foo {}
-   |            ^^^ expected integer, found enum `Option`
-   |
-   = note: expected type `{integer}`
-              found enum `Option<{integer}>`
-
 error[E0308]: mismatched types
   --> $DIR/if-let-typo.rs:9:8
    |
@@ -64,7 +55,7 @@ LL |     if let 3 = foo {}
    |        ^^^
 
 error[E0658]: destructuring assignments are unstable
-  --> $DIR/if-let-typo.rs:11:16
+  --> $DIR/if-let-typo.rs:10:16
    |
 LL |     if Some(3) = foo {}
    |        ------- ^
@@ -75,20 +66,20 @@ LL |     if Some(3) = foo {}
    = help: add `#![feature(destructuring_assignment)]` to the crate attributes to enable
 
 error[E0070]: invalid left-hand side of assignment
-  --> $DIR/if-let-typo.rs:11:16
+  --> $DIR/if-let-typo.rs:10:16
    |
 LL |     if Some(3) = foo {}
    |             -  ^
    |             |
    |             cannot assign to this expression
 
 error[E0308]: mismatched types
-  --> $DIR/if-let-typo.rs:11:8
+  --> $DIR/if-let-typo.rs:10:8
    |
 LL |     if Some(3) = foo {}
    |        ^^^^^^^^^^^^^ expected `bool`, found `()`
 
-error: aborting due to 10 previous errors
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0070, E0308, E0425, E0658.
 For more information about an error, try `rustc --explain E0070`.