rust-lang · bors · Nov 24, 2019 · Nov 19, 2019
diff --git a/src/librustc_typeck/check/demand.rs b/src/librustc_typeck/check/demand.rs
@@ -102,12 +102,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     // N.B., this code relies on `self.diverges` to be accurate. In
     // particular, assignments to `!` will be permitted if the
     // diverges flag is currently "always".
-    pub fn demand_coerce_diag(&self,
-                              expr: &hir::Expr,
-                              checked_ty: Ty<'tcx>,
-                              expected: Ty<'tcx>,
-                              allow_two_phase: AllowTwoPhase)
-                              -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
+    pub fn demand_coerce_diag(
+        &self,
+        expr: &hir::Expr,
+        checked_ty: Ty<'tcx>,
+        expected: Ty<'tcx>,
+        allow_two_phase: AllowTwoPhase,
+    ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
         let expected = self.resolve_vars_with_obligations(expected);
 
         let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
@@ -126,6 +127,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             return (expected, None)
         }
 
+        self.annotate_expected_due_to_let_ty(&mut err, expr);
         self.suggest_compatible_variants(&mut err, expr, expected, expr_ty);
         self.suggest_ref_or_into(&mut err, expr, expected, expr_ty);
         self.suggest_boxing_when_appropriate(&mut err, expr, expected, expr_ty);
@@ -134,6 +136,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         (expected, Some(err))
     }
 
+    fn annotate_expected_due_to_let_ty(&self, err: &mut DiagnosticBuilder<'_>, expr: &hir::Expr) {
+        let parent = self.tcx.hir().get_parent_node(expr.hir_id);
+        if let Some(hir::Node::Local(hir::Local {
+            ty: Some(ty),
+            init: Some(init),
+            ..
+        })) = self.tcx.hir().find(parent) {
+            if init.hir_id == expr.hir_id {
+                // Point at `let` assignment type.
+                err.span_label(ty.span, "expected due to this");
+            }
+        }
+    }
+
     /// Returns whether the expected type is `bool` and the expression is `x = y`.
     pub fn is_assign_to_bool(&self, expr: &hir::Expr, expected: Ty<'tcx>) -> bool {
         if let hir::ExprKind::Assign(..) = expr.kind {

diff --git a/src/test/rustdoc-ui/failed-doctest-missing-codes.stdout b/src/test/rustdoc-ui/failed-doctest-missing-codes.stdout
@@ -9,7 +9,9 @@ error[E0308]: mismatched types
   --> $DIR/failed-doctest-missing-codes.rs:9:13
    |
 LL | let x: () = 5i32;
-   |             ^^^^ expected `()`, found `i32`
+   |        --   ^^^^ expected `()`, found `i32`
+   |        |
+   |        expected due to this
 
 error: aborting due to previous error
 

diff --git a/src/test/ui/array-not-vector.stderr b/src/test/ui/array-not-vector.stderr
@@ -2,13 +2,17 @@ error[E0308]: mismatched types
   --> $DIR/array-not-vector.rs:2:19
    |
 LL |     let _x: i32 = [1, 2, 3];
-   |                   ^^^^^^^^^ expected `i32`, found array `[{integer}; 3]`
+   |             ---   ^^^^^^^^^ expected `i32`, found array `[{integer}; 3]`
+   |             |
+   |             expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/array-not-vector.rs:7:20
    |
 LL |     let _y: &i32 = x;
-   |                    ^ expected `i32`, found slice `[i32]`
+   |             ----   ^ expected `i32`, found slice `[i32]`
+   |             |
+   |             expected due to this
    |
    = note: expected reference `&i32`
               found reference `&[i32]`

diff --git a/src/test/ui/associated-types/associated-types-eq-3.stderr b/src/test/ui/associated-types/associated-types-eq-3.stderr
@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/associated-types-eq-3.rs:23:18
    |
 LL |     let _: Bar = x.boo();
-   |                  ^^^^^^^ expected struct `Bar`, found associated type
+   |            ---   ^^^^^^^ expected struct `Bar`, found associated type
+   |            |
+   |            expected due to this
    |
    = note:       expected struct `Bar`
            found associated type `<I as Foo>::A`

diff --git a/src/test/ui/associated-types/associated-types-path-2.stderr b/src/test/ui/associated-types/associated-types-path-2.stderr
@@ -43,7 +43,9 @@ error[E0308]: mismatched types
   --> $DIR/associated-types-path-2.rs:41:18
    |
 LL |     let _: i32 = f2(2i32);
-   |                  ^^^^^^^^ expected `i32`, found `u32`
+   |            ---   ^^^^^^^^ expected `i32`, found `u32`
+   |            |
+   |            expected due to this
    |
 help: you can convert an `u32` to `i32` and panic if the converted value wouldn't fit
    |

diff --git a/src/test/ui/c-variadic/variadic-ffi-1.stderr b/src/test/ui/c-variadic/variadic-ffi-1.stderr
@@ -26,7 +26,9 @@ error[E0308]: mismatched types
   --> $DIR/variadic-ffi-1.rs:19:56
    |
 LL |         let x: unsafe extern "C" fn(f: isize, x: u8) = foo;
-   |                                                        ^^^ expected non-variadic fn, found variadic function
+   |                -------------------------------------   ^^^ expected non-variadic fn, found variadic function
+   |                |
+   |                expected due to this
    |
    = note: expected fn pointer `unsafe extern "C" fn(isize, u8)`
                  found fn item `unsafe extern "C" fn(isize, u8, ...) {foo}`
@@ -35,7 +37,9 @@ error[E0308]: mismatched types
   --> $DIR/variadic-ffi-1.rs:20:54
    |
 LL |         let y: extern "C" fn(f: isize, x: u8, ...) = bar;
-   |                                                      ^^^ expected variadic fn, found non-variadic function
+   |                -----------------------------------   ^^^ expected variadic fn, found non-variadic function
+   |                |
+   |                expected due to this
    |
    = note: expected fn pointer `extern "C" fn(isize, u8, ...)`
                  found fn item `extern "C" fn(isize, u8) {bar}`

diff --git a/src/test/ui/closures/closure-no-fn-1.stderr b/src/test/ui/closures/closure-no-fn-1.stderr
@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/closure-no-fn-1.rs:6:29
    |
 LL |     let foo: fn(u8) -> u8 = |v: u8| { a += v; a };
-   |                             ^^^^^^^^^^^^^^^^^^^^^ expected fn pointer, found closure
+   |              ------------   ^^^^^^^^^^^^^^^^^^^^^ expected fn pointer, found closure
+   |              |
+   |              expected due to this
    |
    = note: expected fn pointer `fn(u8) -> u8`
                  found closure `[closure@$DIR/closure-no-fn-1.rs:6:29: 6:50 a:_]`

diff --git a/src/test/ui/closures/closure-no-fn-2.stderr b/src/test/ui/closures/closure-no-fn-2.stderr
@@ -2,7 +2,9 @@ error[E0308]: mismatched types
   --> $DIR/closure-no-fn-2.rs:6:27
    |
 LL |     let bar: fn() -> u8 = || { b };
-   |                           ^^^^^^^^ expected fn pointer, found closure
+   |              ----------   ^^^^^^^^ expected fn pointer, found closure
+   |              |
+   |              expected due to this
    |
    = note: expected fn pointer `fn() -> u8`
                  found closure `[closure@$DIR/closure-no-fn-2.rs:6:27: 6:35 b:_]`

diff --git a/src/test/ui/coercion/coerce-to-bang.stderr b/src/test/ui/coercion/coerce-to-bang.stderr
@@ -47,7 +47,9 @@ error[E0308]: mismatched types
   --> $DIR/coerce-to-bang.rs:48:21
    |
 LL |     let x: [!; 2] = [return, 22];
-   |                     ^^^^^^^^^^^^ expected `!`, found integer
+   |            ------   ^^^^^^^^^^^^ expected `!`, found integer
+   |            |
+   |            expected due to this
    |
    = note: expected array `[!; 2]`
               found array `[{integer}; 2]`

diff --git a/src/test/ui/coercion/coercion-slice.stderr b/src/test/ui/coercion/coercion-slice.stderr
@@ -2,10 +2,11 @@ error[E0308]: mismatched types
   --> $DIR/coercion-slice.rs:4:21
    |
 LL |     let _: &[i32] = [0];
-   |                     ^^^
-   |                     |
-   |                     expected `&[i32]`, found array `[{integer}; 1]`
-   |                     help: consider borrowing here: `&[0]`
+   |            ------   ^^^
+   |            |        |
+   |            |        expected `&[i32]`, found array `[{integer}; 1]`
+   |            |        help: consider borrowing here: `&[0]`
+   |            expected due to this
 
 error: aborting due to previous error
 

diff --git a/src/test/ui/const-generics/fn-const-param-infer.stderr b/src/test/ui/const-generics/fn-const-param-infer.stderr
@@ -10,7 +10,9 @@ error[E0308]: mismatched types
   --> $DIR/fn-const-param-infer.rs:16:31
    |
 LL |     let _: Checked<not_one> = Checked::<not_two>;
-   |                               ^^^^^^^^^^^^^^^^^^ expected `not_one`, found `not_two`
+   |            ----------------   ^^^^^^^^^^^^^^^^^^ expected `not_one`, found `not_two`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `Checked<not_one>`
               found struct `Checked<not_two>`
@@ -34,7 +36,9 @@ error[E0308]: mismatched types
   --> $DIR/fn-const-param-infer.rs:25:40
    |
 LL |     let _: Checked<{generic::<u32>}> = Checked::<{generic::<u16>}>;
-   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `generic::<u32>`, found `generic::<u16>`
+   |            -------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `generic::<u32>`, found `generic::<u16>`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `Checked<generic::<u32>>`
               found struct `Checked<generic::<u16>>`

diff --git a/src/test/ui/const-generics/raw-ptr-const-param.stderr b/src/test/ui/const-generics/raw-ptr-const-param.stderr
@@ -10,7 +10,9 @@ error[E0308]: mismatched types
   --> $DIR/raw-ptr-const-param.rs:7:38
    |
 LL |     let _: Const<{15 as *const _}> = Const::<{10 as *const _}>;
-   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{pointer}`, found `{pointer}`
+   |            -----------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{pointer}`, found `{pointer}`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `Const<{pointer}>`
               found struct `Const<{pointer}>`

diff --git a/src/test/ui/const-generics/slice-const-param-mismatch.stderr b/src/test/ui/const-generics/slice-const-param-mismatch.stderr
@@ -10,7 +10,9 @@ error[E0308]: mismatched types
   --> $DIR/slice-const-param-mismatch.rs:9:35
    |
 LL |     let _: ConstString<"Hello"> = ConstString::<"World">;
-   |                                   ^^^^^^^^^^^^^^^^^^^^^^ expected `"Hello"`, found `"World"`
+   |            --------------------   ^^^^^^^^^^^^^^^^^^^^^^ expected `"Hello"`, found `"World"`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `ConstString<"Hello">`
               found struct `ConstString<"World">`
@@ -19,7 +21,9 @@ error[E0308]: mismatched types
   --> $DIR/slice-const-param-mismatch.rs:11:33
    |
 LL |     let _: ConstString<"ℇ㇈↦"> = ConstString::<"ℇ㇈↥">;
-   |                                  ^^^^^^^^^^^^^^^^^^^^^ expected `"ℇ㇈↦"`, found `"ℇ㇈↥"`
+   |            -------------------   ^^^^^^^^^^^^^^^^^^^^^ expected `"ℇ㇈↦"`, found `"ℇ㇈↥"`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `ConstString<"ℇ㇈↦">`
               found struct `ConstString<"ℇ㇈↥">`
@@ -28,7 +32,9 @@ error[E0308]: mismatched types
   --> $DIR/slice-const-param-mismatch.rs:13:33
    |
 LL |     let _: ConstBytes<b"AAA"> = ConstBytes::<b"BBB">;
-   |                                 ^^^^^^^^^^^^^^^^^^^^ expected `b"AAA"`, found `b"BBB"`
+   |            ------------------   ^^^^^^^^^^^^^^^^^^^^ expected `b"AAA"`, found `b"BBB"`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `ConstBytes<b"AAA">`
               found struct `ConstBytes<b"BBB">`

diff --git a/src/test/ui/const-generics/types-mismatch-const-args.stderr b/src/test/ui/const-generics/types-mismatch-const-args.stderr
@@ -10,7 +10,9 @@ error[E0308]: mismatched types
   --> $DIR/types-mismatch-const-args.rs:13:41
    |
 LL |     let _: A<'a, u32, {2u32}, {3u32}> = A::<'a, u32, {4u32}, {3u32}> { data: PhantomData };
-   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `2u32`, found `4u32`
+   |            --------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `2u32`, found `4u32`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `A<'_, _, 2u32, _>`
               found struct `A<'_, _, 4u32, _>`
@@ -19,7 +21,9 @@ error[E0308]: mismatched types
   --> $DIR/types-mismatch-const-args.rs:15:41
    |
 LL |     let _: A<'a, u16, {2u32}, {3u32}> = A::<'b, u32, {2u32}, {3u32}> { data: PhantomData };
-   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u16`, found `u32`
+   |            --------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u16`, found `u32`
+   |            |
+   |            expected due to this
    |
    = note: expected struct `A<'a, u16, _, _>`
               found struct `A<'b, u32, _, _>`

diff --git a/src/test/ui/conversion-methods.stderr b/src/test/ui/conversion-methods.stderr
@@ -2,37 +2,41 @@ error[E0308]: mismatched types
   --> $DIR/conversion-methods.rs:5:41
    |
 LL |     let _tis_an_instants_play: String = "'Tis a fond Ambush—";
-   |                                         ^^^^^^^^^^^^^^^^^^^^^
-   |                                         |
-   |                                         expected struct `std::string::String`, found `&str`
-   |                                         help: try using a conversion method: `"'Tis a fond Ambush—".to_string()`
+   |                                ------   ^^^^^^^^^^^^^^^^^^^^^
+   |                                |        |
+   |                                |        expected struct `std::string::String`, found `&str`
+   |                                |        help: try using a conversion method: `"'Tis a fond Ambush—".to_string()`
+   |                                expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/conversion-methods.rs:6:40
    |
 LL |     let _just_to_make_bliss: PathBuf = Path::new("/ern/her/own/surprise");
-   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |                                        |
-   |                                        expected struct `std::path::PathBuf`, found `&std::path::Path`
-   |                                        help: try using a conversion method: `Path::new("/ern/her/own/surprise").to_path_buf()`
+   |                              -------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                              |         |
+   |                              |         expected struct `std::path::PathBuf`, found `&std::path::Path`
+   |                              |         help: try using a conversion method: `Path::new("/ern/her/own/surprise").to_path_buf()`
+   |                              expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/conversion-methods.rs:9:40
    |
 LL |     let _but_should_the_play: String = 2; // Perhaps surprisingly, we suggest .to_string() here
-   |                                        ^
-   |                                        |
-   |                                        expected struct `std::string::String`, found integer
-   |                                        help: try using a conversion method: `2.to_string()`
+   |                               ------   ^
+   |                               |        |
+   |                               |        expected struct `std::string::String`, found integer
+   |                               |        help: try using a conversion method: `2.to_string()`
+   |                               expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/conversion-methods.rs:12:47
    |
 LL |     let _prove_piercing_earnest: Vec<usize> = &[1, 2, 3];
-   |                                               ^^^^^^^^^^
-   |                                               |
-   |                                               expected struct `std::vec::Vec`, found `&[{integer}; 3]`
-   |                                               help: try using a conversion method: `(&[1, 2, 3]).to_vec()`
+   |                                  ----------   ^^^^^^^^^^
+   |                                  |            |
+   |                                  |            expected struct `std::vec::Vec`, found `&[{integer}; 3]`
+   |                                  |            help: try using a conversion method: `(&[1, 2, 3]).to_vec()`
+   |                                  expected due to this
    |
    = note: expected struct `std::vec::Vec<usize>`
            found reference `&[{integer}; 3]`

diff --git a/src/test/ui/cross/cross-borrow-trait.stderr b/src/test/ui/cross/cross-borrow-trait.stderr
@@ -2,10 +2,11 @@ error[E0308]: mismatched types
   --> $DIR/cross-borrow-trait.rs:10:26
    |
 LL |     let _y: &dyn Trait = x;
-   |                          ^
-   |                          |
-   |                          expected `&dyn Trait`, found struct `std::boxed::Box`
-   |                          help: consider borrowing here: `&x`
+   |             ----------   ^
+   |             |            |
+   |             |            expected `&dyn Trait`, found struct `std::boxed::Box`
+   |             |            help: consider borrowing here: `&x`
+   |             expected due to this
    |
    = note: expected reference `&dyn Trait`
                  found struct `std::boxed::Box<dyn Trait>`

diff --git a/src/test/ui/did_you_mean/issue-53280-expected-float-found-integer-literal.stderr b/src/test/ui/did_you_mean/issue-53280-expected-float-found-integer-literal.stderr
@@ -2,40 +2,47 @@ error[E0308]: mismatched types
   --> $DIR/issue-53280-expected-float-found-integer-literal.rs:2:24
    |
 LL |     let sixteen: f32 = 16;
-   |                        ^^
-   |                        |
-   |                        expected `f32`, found integer
-   |                        help: use a float literal: `16.0`
+   |                  ---   ^^
+   |                  |     |
+   |                  |     expected `f32`, found integer
+   |                  |     help: use a float literal: `16.0`
+   |                  expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/issue-53280-expected-float-found-integer-literal.rs:5:38
    |
 LL |     let a_million_and_seventy: f64 = 1_000_070;
-   |                                      ^^^^^^^^^
-   |                                      |
-   |                                      expected `f64`, found integer
-   |                                      help: use a float literal: `1_000_070.0`
+   |                                ---   ^^^^^^^^^
+   |                                |     |
+   |                                |     expected `f64`, found integer
+   |                                |     help: use a float literal: `1_000_070.0`
+   |                                expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/issue-53280-expected-float-found-integer-literal.rs:8:30
    |
 LL |     let negative_nine: f32 = -9;
-   |                              ^^
-   |                              |
-   |                              expected `f32`, found integer
-   |                              help: use a float literal: `-9.0`
+   |                        ---   ^^
+   |                        |     |
+   |                        |     expected `f32`, found integer
+   |                        |     help: use a float literal: `-9.0`
+   |                        expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/issue-53280-expected-float-found-integer-literal.rs:15:30
    |
 LL |     let sixteen_again: f64 = 0x10;
-   |                              ^^^^ expected `f64`, found integer
+   |                        ---   ^^^^ expected `f64`, found integer
+   |                        |
+   |                        expected due to this
 
 error[E0308]: mismatched types
   --> $DIR/issue-53280-expected-float-found-integer-literal.rs:17:30
    |
 LL |     let and_once_more: f32 = 0o20;
-   |                              ^^^^ expected `f32`, found integer
+   |                        ---   ^^^^ expected `f32`, found integer
+   |                        |
+   |                        expected due to this
 
 error: aborting due to 5 previous errors