Further dedup unsized locals errors involving method calls

Author: estebank

compiler/rustc_hir_typeck/src/gather_locals.rs

@@ -138,22 +138,32 @@ impl<'a, 'tcx> GatherLocalsVisitor<'a, 'tcx> {
             self.fcx.ty_to_string(*self.fcx.locals.borrow().get(&decl.hir_id).unwrap())
         );
     }
+
+    fn span_for_init_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> Span {
+        // In other parts of the compiler, when emitting a bound error on a method call we point at
+        // the method call path. We mimic that here so that error deduplication will work as
+        // expected.
+        match expr.kind {
+            hir::ExprKind::MethodCall(path, ..) => path.ident.span,
+            _ => expr.span,
+        }
+    }
 }
 
 impl<'a, 'tcx> Visitor<'tcx> for GatherLocalsVisitor<'a, 'tcx> {
     // Add explicitly-declared locals.
     fn visit_local(&mut self, local: &'tcx hir::LetStmt<'tcx>) {
         self.declare(local.into());
         let sp = self.let_binding_init.take();
-        self.let_binding_init = local.init.map(|e| e.span);
+        self.let_binding_init = local.init.map(|e| self.span_for_init_expr(e));
         intravisit::walk_local(self, local);
         self.let_binding_init = sp;
     }
 
     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
         let sp = self.let_binding_init.take();
         if let hir::ExprKind::Let(let_expr) = expr.kind {
-            self.let_binding_init = Some(let_expr.init.span);
+            self.let_binding_init = Some(self.span_for_init_expr(&let_expr.init));
             self.declare((let_expr, expr.hir_id).into());
         }
         intravisit::walk_expr(self, expr);

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -139,6 +139,12 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             span = local.pat.span;
                         }
                     }
+                    ObligationCauseCode::ExprBindingObligation(_, _, hir_id, _) => {
+                        // For method calls like `let x = y.foo();` that are `?Sized`, we also dedup
+                        if let hir::Node::Local(local) = self.tcx.parent_hir_node(*hir_id) {
+                            span = local.pat.span;
+                        }
+                    }
                     _ => {}
                 }
             }

tests/ui/associated-types/associated-types-unsized.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the size for values of type `<T as Get>::Value` cannot be known at compilation time
-  --> $DIR/associated-types-unsized.rs:10:13
+  --> $DIR/associated-types-unsized.rs:10:15
    |
 LL |     let x = t.get();
-   |             ^^^^^^^ doesn't have a size known at compile-time
+   |               ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `<T as Get>::Value`
    = note: all local variables must have a statically known size

tests/ui/error-codes/E0038.stderr

@@ -29,10 +29,10 @@ LL |     fn foo(&self) -> Self;
    = help: consider moving `foo` to another trait
 
 error[E0277]: the size for values of type `dyn Trait` cannot be known at compilation time
-  --> $DIR/E0038.rs:7:13
+  --> $DIR/E0038.rs:7:15
    |
 LL |     let y = x.foo();
-   |             ^^^^^^^ doesn't have a size known at compile-time
+   |               ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `dyn Trait`
    = note: all local variables must have a statically known size

tests/ui/iterators/collect-into-slice.rs

@@ -5,14 +5,11 @@ fn process_slice(data: &[i32]) {
 fn main() {
     let some_generated_vec = (0..10).collect();
     //~^ ERROR the size for values of type `[i32]` cannot be known at compilation time
-    //~| ERROR the size for values of type `[i32]` cannot be known at compilation time
     //~| ERROR a slice of type `[i32]` cannot be built since `[i32]` has no definite size
     //~| NOTE try explicitly collecting into a `Vec<{integer}>`
-    //~| NOTE required by an implicit `Sized` bound in `collect`
     //~| NOTE required by a bound in `collect`
     //~| NOTE all local variables must have a statically known size
     //~| NOTE doesn't have a size known at compile-time
-    //~| NOTE doesn't have a size known at compile-time
     process_slice(&some_generated_vec);
 
     let some_generated_vec = (0..10).collect();

tests/ui/iterators/collect-into-slice.stderr

@@ -8,28 +8,18 @@ LL |     let some_generated_vec = (0..10).collect();
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 
-error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
-  --> $DIR/collect-into-slice.rs:6:30
-   |
-LL |     let some_generated_vec = (0..10).collect();
-   |                              ^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `[i32]`
-   = note: all local variables must have a statically known size
-   = help: unsized locals are gated as an unstable feature
-
 error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
   --> $DIR/collect-into-slice.rs:6:38
    |
 LL |     let some_generated_vec = (0..10).collect();
    |                                      ^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i32]`
-note: required by an implicit `Sized` bound in `collect`
-  --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
 
 error[E0277]: a slice of type `&[i32]` cannot be built since we need to store the elements somewhere
-  --> $DIR/collect-into-slice.rs:18:38
+  --> $DIR/collect-into-slice.rs:15:38
    |
 LL |     let some_generated_vec = (0..10).collect();
    |                                      ^^^^^^^ try explicitly collecting into a `Vec<{integer}>`
@@ -38,6 +28,6 @@ LL |     let some_generated_vec = (0..10).collect();
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0277`.