Pass the span of <init> in let <pat> = <init>;

when type checking `<pat>`.

src/librustc_typeck/check/mod.rs

@@ -4275,17 +4275,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     pub fn check_decl_local(&self, local: &'tcx hir::Local<'tcx>) {
-        let t = self.local_ty(local.span, local.hir_id).decl_ty;
+        let ty = self.local_ty(local.span, local.hir_id).decl_ty;
-        self.write_ty(local.hir_id, t);
+        self.write_ty(local.hir_id, ty);
 
         if let Some(ref init) = local.init {
             let init_ty = self.check_decl_initializer(local, &init);
-            self.overwrite_local_ty_if_err(local, t, init_ty);
+            self.overwrite_local_ty_if_err(local, ty, init_ty);
         }
 
-        self.check_pat_top(&local.pat, t, None);
+        self.check_pat_top(&local.pat, ty, local.init.map(|init| init.span));
         let pat_ty = self.node_ty(local.pat.hir_id);
-        self.overwrite_local_ty_if_err(local, t, pat_ty);
+        self.overwrite_local_ty_if_err(local, ty, pat_ty);
     }
 
     fn overwrite_local_ty_if_err(

src/librustc_typeck/check/pat.rs

@@ -59,14 +59,9 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
 }
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
-    pub fn check_pat_top(
+    pub fn check_pat_top(&self, pat: &'tcx Pat<'tcx>, expected: Ty<'tcx>, span: Option<Span>) {
-        &self,
-        pat: &'tcx Pat<'tcx>,
-        expected: Ty<'tcx>,
-        discrim_span: Option<Span>,
-    ) {
         let def_bm = BindingMode::BindByValue(hir::Mutability::Not);
-        self.check_pat(pat, expected, def_bm, discrim_span);
+        self.check_pat(pat, expected, def_bm, span);
     }
 
     /// `discrim_span` argument having a `Span` indicates that this pattern is part of a match

src/test/ui/issues/issue-14541.stderr

@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/issue-14541.rs:5:9
    |
 LL |     let Vec3 { y: _, z: _ } = v;
-   |         ^^^^^^^^^^^^^^^^^^^ expected struct `Vec2`, found struct `Vec3`
+   |         ^^^^^^^^^^^^^^^^^^^   - this expression has type `Vec2`
+   |         |
+   |         expected struct `Vec2`, found struct `Vec3`
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-16338.stderr

@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/issue-16338.rs:7:9
    |
 LL |     let Slice { data: data, len: len } = "foo";
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `str`, found struct `Slice`
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   ----- this expression has type `str`
+   |         |
+   |         expected `str`, found struct `Slice`
    |
    = note: expected type `str`
             found struct `Slice<_>`

src/test/ui/issues/issue-37026.stderr

@@ -8,7 +8,9 @@ error[E0308]: mismatched types
   --> $DIR/issue-37026.rs:7:9
    |
 LL |     let empty_struct::XEmpty6(..) = ();
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found struct `empty_struct::XEmpty6`
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^   -- this expression has type `()`
+   |         |
+   |         expected `()`, found struct `empty_struct::XEmpty6`
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-67037-pat-tup-scrut-ty-diff-less-fields.stderr

@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/issue-67037-pat-tup-scrut-ty-diff-less-fields.rs:19:9
    |
 LL |     let P() = U {};
-   |         ^^^ expected struct `U`, found struct `P`
+   |         ^^^   ---- this expression has type `U`
+   |         |
+   |         expected struct `U`, found struct `P`
    |
    = note: expected struct `U`
               found struct `P<_>`